Truck Farm: a Mobile Educational Garden Experiment

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For a couple of years my wife and I lived in a small townhouse/duplex in Southern California with no yard and a back patio that was perpetually in the shade.

I'd always wanted to try growing my own food, and I felt like because I finally had my "own place," it would give me a good opportunity... but I had no space.

One night I started brainstorming about whether or not I could start a raised bed on the back patio with shade-friendly plants. It turns out most plants like light. A lot.

After that I thought about contacting our homeowners association and seeing if they'd be ok with me using some of the public space to start a garden... maybe even a community garden. The HOA decided it would detract from the aesthetic appeal of the property. Furthermore, because I was a renter, I didn't have much say in what the HOA said I could or couldn't do.

Fast forward a couple of weeks, and a random thought occurred to me late one night. I had a Toyota Tacoma that I bought with money from a deployment (rookie mistake, but what's done is done), and which I had used as a truck all of maybe 5 times in the 3 years I had owned it. It was a fun truck to drive, but it wasn't getting used as a truck.

The pieces started falling into place. I decided I would try to make a mobile farm/garden in my truck bed! As I researched it that night, I found others who had attempted it as well, which validated the idea. I used some of their designs as a baseline and got started.

Step 1: Truck Farm Goals

I hadn't ever built... well... anything, before. I had no woodworking experience. No gardening experience. No electronics experience. I had training as a Marine, which served me very well for "Marine things," but left me unprepared for projects like this. Luckily necessity is the mother of invention, and I needed a garden at this point!

So first things first, I decided to set my goals and overall expectations of where I wanted the project to be when complete.

Be Mobile. Being mobile would allow me to get around the barrier of not having any sunlight. In fact, I would be able to move my truck as needed to be in the sun all the time this way!
Be Lightweight. My truck was a Toyota Tacoma which is on a SUV chassis (or so I'm told) and not built for 1-ton+ loads as far as I know. I would need the garden to be comparatively lightweight if I would want it to last. More on this later.
Look Cool. I figured if I was going to do something as crazy as drive around with a greenhouse/garden in the back of my truck, I'd at least want it to look good and professional
Withstand Freeway Speeds. This was a very important goal. I didn't do any studies on drag or wind resistance (maybe I should have). Being in SoCal, much of my driving would occur on the freeway. I would need the garden to be secure enough that I wouldn't lose plants/pieces.
Be Functional. I'd actually want to GROW STUFF in this garden. I had hoped to provide all, or most of my wife and my produce needs through my truck farm, which would help us save money at the grocery store.
Be Educational. I wanted to be able to use the truck farm as a means of educating other people interested in learning about growing their own food. Moreover, I wanted to learn something myself. I chose to incorporate automated watering, temperature sensors and cooling systems in order to give myself some experience in Arduino and electronics.

With my list of goals more or less complete, I went to the drawing board.

MATERIALS AND EQUIPMENT NEEDED FOR THE GREENHOUSE:

Framing Wood. I built the frame out of 1x2 redwood. It is more expensive than standard pine, but is much more resistant to moisture and rot, which would be important or this project.
Siding Wood. Siding was cheap plywood or OSB. Do not use straight particle board or MDF, as they do not withstand moisture well at all, and will crumble over time.
Acrylic or Polycarbonate Sheets. You have a couple of options for the "glass" of the greenhouse. Plexiglas is a brand name of acrylic sheets. You're probably best looking in a big Blue or Orange store, but if Amazon is your game, I recommend optix acrylic sheets. The thickness is up to your preference; you want it to be thick enough to be durable, but not so thick as to be too heavy. Alternatively, if you have a little more money to spend, I would recommend Lexan polycarbonate sheets. Lexan is the brand name, but polycarbonate is typically much more durable than acrylic, and also slightly more resistant to sun damage over longer periods of time. Both acrylic and polycarbonate are durable and effective, it just depends on your budget.
EPDM Pond Liner. I bought this Firestone EPDM pond liner because I'd heard that Firestone PondGard was the best pond liner available. It was slightly expensive and probably overkill, but I knew that there would be no chemicals leaching from it into my soil. Don't get PVC for that reason. And between HDPE and EPDM, I've heard a lot of debate.
Drainage Mat. The drainage mat I bought was made by MiraDrain and is among the more high-end drainage mats on the market. I wouldn't necessarily advise going so high-end, since I could only find it by the roll. This was the hardest material to find, and unfortunately I can't seem to find a cheap equivalent for it on Amazon. Your mileage may vary, but I wouldn't leave it out.
Electric Drill. A good, functional drill is essential. For most of the project I used a cheap, wired Black and Decker drill. It's something I already had on hand and it was enough to get by. I really would recommend a high quality cordless drill though. Once I got about halfway through, I justified buying a much nicer DeWALT 18v Cordless Drill. 18v was all the rage at the time, but if I were buying today, I would go with a 20v DeWALT. You can monitor Amazon for occasional deals and bundles on cordless drills.
Miter Box and Saw. For the majority of the project, I made all of my cuts by hand using this Stanley miter box and saw. The 1x2 redwood lumber is small enough that it didn't take long to make cuts. Towards the end of the project, I splurged and bought this DeWALT Double Bevel Sliding Compound Miter Saw. It is expensive, but if you have any desire to make additional projects it is a beast of a machine and one of my favorite tools of all time
Circular Saw or Table Saw. I didn't have a table saw for this project. I didn't have enough room for one, to be honest. Eventually I bought a cheap Skil table saw, but for this whole project I made my plywood cuts using this Skil circular saw. For fine plywood cuts, what's really important is the blade. But what I will say is that just like the drill, if I had to do it again, I would get a good 18v or 20v cordless circular saws like these. My preference is DeWALT, but I also have heard good things about Makita.
Circular Saw Track/Guide. For this project, I wasn't aware of this product. If I had to do it again I'd get a Kreg accu-cut circular saw guide in a heartbeat. Other companies (like DeWALT) make circular saw tracks as well, but I'm a huge supporter of Kreg and this is an awesome product. For all of my plywood cuts I used two flimsy saw horses and a crude track I made from a long ruler. The Kreg accu-cut makes rip cuts on plywood super simple.
Jig Saw. I had a wired Skil jig saw that I used to cut out the holes for my cooling fans. Make sure you use a fine blade if you choose to do so. In hindsight I would have much preferred to have a cordless one, like this 20v beast from DeWalt. My corded one worked fine, but the wires really do become a pain, and I found myself constantly trying to keep the cord out of the way while cutting.
Saw Horses. In the beginning I made all of my cuts and did all of my assembly on the garage floor. It didn't take me long to see the value in saw horses. I set a couple pieces of wood across a cheap plastic set of them and used them as a makeshift table for the remainder of my cuts. You can splurge and buy really nice ones, or you can get a cheap set of plastic ones that have basic functionality like saw horses by Stanley. Your back will say thank you.
Wood Screws and Machine Screws. What screws you use is really up to you. I used some higher quality coated torx exterior wood screws. If you go with torx screws, make sure you get the appropriate bit for your drill as well; I find that torx screws are much easier to work with than phillips or flatheads. Machine screws will be used to attach your plexiglas/acrylic sheets. Make sure they have a flat head, and that you use a washer with them. These are a dime a dozen so shop around and get what's available, as long as they can be used exterior.
Primer, Paint and Brushes. I'm not an expert with paint, so this is up for debate. But my preference for primer is latex primer by Kilz. I've also heard that Zinsser primer is good as well, but have not used it. I don't have any real reason for recommending a water or latex based primer and paint other than it being lower VOC, and I don't like the idea of oil-based products being in potential contact with my food. For paint it's really up to you. Everyone I spoke to (at orange blue stores) recommended paint brushes by Purdy. They are somewhat expensive and people online seem to like them too. I also heard good things about Wooster paint brushes but didn't try them. I will say that the Purdy brushes I used seemed like they were high quality, but they streaked a lot with the paint I used. It could be that I used low quality paint, or it could be that my brushing technique has much to be desired. Your mileage may very on brushes.

MATERIALS AND EQUIPMENT FOR THE IRRIGATION AND VENTILATION:

If you choose to take the next step and try out a ventilation and irrigation system, here are some of the materials I used.

Water Pump. Not everyone (actually, probably no one) will use the exact same setup I used for my watering system. Here is a 10w submersible water pump that is very similar to the one I used originally. I tried both submersible and dry pumps. They are relatively cheap and most are probably made in China. The important things to think about are the power consumption and the height it can pump. Many cheaper pumps will not be able to handle the volume or distance you'll want to pump the water, so be cautious. You'll also have to decide on a pump based on your power availability.
Toilet Float. The way you create your float system is not set in stone. I chose this because it was cheap and because it used stuff I had on hand. You can get a cheap toilet float on Amazon and be on your way, or you can go with a slightly more elegant float valve.
Momentary Lever Switch. I used a momentary lever switch that I had laying around. You'll want a switch that offers some resistance and will be somewhat durable. Again, there might be better ways to do this than what I did. Amazon has a large collection of momentary lever switches you can look through. They're fairly easy to wire, regardless of which you choose, and come in either normally on or normally off configurations.
Arduino Uno. I used an Arduino Uno R3 to run this setup. It was easy to learn on. You can buy kits that include jumper wires, breadboards and multiple other shields and sensors. Really up to you.
Arduino Relay Shield. There are a lot of flavors and options for electronic relays. I was still learning at the time, and so a simple relay shield like these helped me get things going a little quicker. It plugs directly into your Arduino Uno and allows you control of several relays based on inputs. Pretty simple to use once you figure out the Arduino itself.
DC/AC Inverter. Again, the choice of inverter will depend on what type of pump you get, as well as your power input. You can shop around for dc inverter like one of these if you have an AC pump. If you have a DC pump then it can run straight off your battery.
Battery. I used a 7 amp hour 12v sealed lead acid battery. I already had this battery on hand, and I kind of designed the system around its capacity. It fit neatly into my battery box. Starting over, I would probably get a deep cycle Marine battery, but those can be prohibitively expensive. It's important to keep the battery secured, dry, and occasionally check on it.
Solar Panels and Charger/Regulator. I used two 5w 12v solar panels, wired in parallel to a 15w 12v solar panel, for a total 25w nominal power supply. This was good enough for my purposes, and it utilized stuff that I already had on hand. I connected the panels to a solar charge controller, which helps regulate the charging of the battery, prevents current from feeding backwards into the panels, and helps keep the battery topped off correctly, which supposedly extends the batteries life. A charge controller isn't essential, but it is critical.
Computer Case Fans. I used these computer case fans for my ventilation. They don't consume a lot of power and can run straight off the battery without much fuss.
Sensors. If you want to learn a lot more about Arduino, you can follow my lead and get a temperature and humidity sensor like one of these. I used these to program my Arduino to turn the ventilation fans on automatically if the temperature or interior humidity got too high -- like if I left the greenhouse windows closed by mistake during the day.

Whew! Ok, so that's a pretty exhaustive list, but it's probably not 100% everything. You'll need additional knick-knacks here and there (if you want) like screws, aluminum rods, jumper wires, and breadboards, among other things. There are some decent jumper wire and breadboard kits out there if you search around, or you can just piece it together as you go.

A lot of it you can buy as you go, and as you decide whether you want to incorporate it into your design or not.

Step 2: Plan, Plan, Plan

If you're a total amateur like me, you may not know where to start with your planning phase.

I hadn't discovered Google Sketchup yet at this point in my life, and so all of my planning was done with crude sketches on graph paper. In retrospect, I could have followed my own advice and been much more exacting in my planning.

Alas, most of my measurements were ballparks. Most of my cuts were done more than once. Many of my ideas didn't pan out. And quite a few tweaks and additions were made to compensate for errors or lack of planning. Don't be like me. Plan ahead.

Where possible, compensate for things like wheel wells in your truck bed. Understand what kind of bed liner you have, if any. Also understand that water can be both life giving and also very destructive... especially to metal framed vehicles.

Dry fit everything... often. I got lucky that everything fit as expected for the most part. But you don't want to spend all this time building something outside of the truck bed, only to move it and find out it doesn't fit!

Step 3: Begin Building the Frame

All great things start with a good foundation.

The first thing I had to do was build the frame. I had some rough sketches already drawn out, but at this point I was mostly building it as I went along. I would measure one member, cut it, then measure the next part. This is horribly inefficient, but I didn't really know any better at the time.

My design had a main garden box framed out, with a detachable greenhouse top to cover it up. I still hadn't worked out how to build the top at this point, so I just took things one step at a time.

I had also accounted for some form of drainage by building a sloped bottom into the design. I achieved this by just adding some shims/blocks underneath some parts of the frame, on top of which I laid some cheap plywood.

One of my biggest concerns was moisture accumulating in the truck bed. While I had a good bed liner, I didn't want to take any chances with rust. To that end, my design actually elevated the garden bed a couple inches off the actual bed of the truck, and forced excess water out the tailgate.

The frame was then covered with cheap plywood. I wasn't too concerned on wood quality since the wood would either get weatherproofed from painting, or it would be covered by a liner. This was a slight oversight on my part. For any exterior wood project, you should be thinking long term about how to weatherproof your wood. Even if it's not directly exposed to moisture, atmospheric moisture will ultimately compromise it over a long enough time.

The frame is important. The plywood is critical!

I cut a few corners by not surrounding the entire planter box with plywood. The cab-end of the bed was the more raised section, meaning there wouldn't be quite as much soil weight pushing outward. Because of this I chose to save some weight by not bordering this portion with plywood.

The rest of the plywood, however, is very important. The garden soil might not be deep enough to compromise the wood frame on its own. But where the plywood really becomes important is in stabilizing the structure from the forces of wind while driving.

Just like OSB or plywood reinforces the framing of a house, the plywood attached to the frame will keep the farm from becoming a freeway farm. I fastened the plywood using similar exterior wood screws about every foot. It was super stable.

Step 4: Line the Bed With EPDM Liner

I spent a LOT of time researching how best to line the garden bed for water retention, drainage and weight. Given that my garden would be on the roadway a lot, surrounded by airborne chemicals everywhere, I wasn't 100% concerned about being too chemically aware, but I wanted to be as neutral as I could.

My research lead me to decide on EPDM (ethylene propylene diene monomer) as a lining material. It is a type of rubber that is historically very stable. It is not known to leach chemicals into water like other plastics or rubbers are in the presence of sunlight. Other materials you might run into would be PVC, HDPE and LDPE. The HDPE and LDPE are types of polyethylene which are somewhat stable, but are not quite as resistant as HDPE. PVC (polyvinyl chloride) is very much unstable in the presence of sunlight. It is known widely to leach chemicals into soil and water and to rapidly deteriorate when exposed to sunlight.

The clear winner was EPDM. What sold me even more is that it is often used as a pond liner for fish ponds. I figure if the fish aren't dying, it's probably ok to use.

I shopped around and found a roll of EPDM pond liner that would fit my project and allow me a little wiggle room in case I screwed up my measurements.

Create Support

So my next step was to add plywood to the bottom of the planter box. I added several support slats, which were then elevated by a shim. I didn't measure the slope of the plywood, but it was more than adequate. A very minor slope is needed to provide for drainage, so I may have gone a little overboard.

Once that was cut and installed, I laid my EPDM liner into the bed, marked my cuts and then stapled it in place with heavy duty staples. Because I knew I was going to use staples, I made sure to get a fairly thick liner that I wouldn't have to worry about tearing. I also stapled it MANY times in order to distribute the weight to avoid tearing at any one spot.

Along the tailgate end, I left the liner cut and open. I had seen someone else do something similar, and decided I would add a bit of plexiglas to the tail end so that you could see the layers of soil and root structure if you were so inclined.

I was actually surprised to have gotten the liner right on the first try.

Now that my garden bed was waterproofed and elevated to allow excess water to run out of the truck bed, I was on to the next step: the drainage mat.

Step 5: Add a Drainage Layer

This next step is quite possibly overkill. I had seen it used on another similar project and thought it sounded reasonable.

The drainage mat (the one I bought was made by MiraDrain) is a mat with rows of elevated, perforated cones, separated by a semi-permeable landscape fabric.

The mat allows water to trickle out of the soil, out of the perforated cones, and cleanly onto my EPDM liner to drain out the back of the truck. Importantly, it also prevents the soil from accompanying the water. While the water would likely drain out on its own due to the slope, you would ultimately end up with some soil erosion and loss over time if you did not use this.

Drainage mats like this are often used in foundations, basements and other heavy duty, water-saturated situations. For that reason you may think it's excessive (and it very well may be). If you don't use it, you might be ok but you run those risk of losing soil and possibly having an oversaturated bottom layer of soil which might lead to root rot.

I could only find the drainage mat in large rolls. I only needed enough for a small truck bed, and luckily I was able to negotiate a slightly lower price. Still, I ended up with a lot of excess in the hopes that maybe I'd do another project with it some day. Ultimately it sat in my garage for 3 years until I gave it away to someone.

The mat is easy to cut and it interlocks with adjoining layers very easily. I ran the drainage mat along 3 sides and the bottom of the bed and used heavy duty staples to staple it in place.

The garden bed construction was now complete. It was time to move on to the greenhouse portion.

Step 6: Construct the Greenhouse Frame

I built the greenhouse frame in much the same way as the bed frame. One piece at a time, measured and cut, and re-cut.

I didn't use any reinforcing plywood because I knew I was going to use plexiglas, which would effectively serve the same purpose. My biggest concern was keeping it secured to the bed frame underneath it.

I was winging it at this point. I looked at pictures of roof structures on houses and did a loose approximation of what I saw. No research was done into the legality of having this structure on the roadway. I got away with it, so your mileage (haha) may vary.

Originally there was the goal of making the frame more heavy duty. I had thought about using aluminum for the whole thing, but felt the learning curve would have been too difficult. I thought learning to screw wood together was easier than learning to weld or machine aluminum. So I decided to stick with redwood 1x2's with horrible joinery.

I added supporting members along the greenhouse roof to support the plexiglas. I also added supporting structures to where I thought they made sense from an "engineering" perspective (note, I have no engineering experience).

Where my joinery became too complicated (i.e. screws getting in the way of other screws), I ended up buying some metal hardware to give myself more area to screw into. It wasn't elegant. It probably wasn't safe. But it worked!

The greenhouse frame took a long time. Very long. I made so many mistakes in measurement and cutting I possibly increased by costs by 25%. All cuts were done by hand on the floor of a 1 car garage with a cheap miter box and a hand saw. But it finally came together.

I screwed the greenhouse roof to the bed frame with many wood screws. They had the added benefit of clamping the EPDM liner in place as well.

Finally I did a very scientific stress test of the structure by shaking it really hard. It didn't budge, to my amazement.

Step 7: Add Windows

I knew that if I was going to be driving with this thing in my truck bed, I'd have to have a way to enclose it. The enclosure would have to be something that I could somehow take on and off quickly, while still allowing for ventilation and sunlight while on the road.

The solution was to use some piano hinges to secure some framed plexiglas windows onto the sides. Then I sided the roof structure with fixed plexiglas panels on top.

I came up with a very inelegant solution to make the windows open and close. This was not something I had anticipated in the original design, and I winged it. Had I spent more time thinking about it, I'm sure I could have come up with something more functional, but this worked out fine.

I added a couple of screw eyes/hooks to the interior of the greenhouse roof on each side. Through these I inserted an aluminum rod that I had cut to size.

Then, in each of the windows I drilled out a couple small pocket holes that the rod could fit into. On the frame of the bed, I attached a couple small plastic washer thingies I found in the hardware aisle. Then, to open the windows, all I'd have to do is lift them up, remove the rod from the inside, and then brace it between the pocket hole and the plastic washer thingy.

An added benefit is that the way it was set up kept the rods out of the way for the most part while the window was opened. I also added a couple clamps/locks to the side of each window to be able to lock it closed while driving.

This solution ended up being very functional and actually was one of my favorite parts of the build.

Things I thought about but didn't try

I bought a couple self-opening/closing hydraulic pistons with the hopes that I'd have a use for them in opening the windows automatically when the temperature got hot enough. They're filled with a wax or some substance, which, when heated, expands, forcing the piston open. It's actually a really cool, functional device... for a stationary greenhouse. There wasn't a way, however, to disable them for when I was on the road, so I ruled those out.

After I had implemented my aluminum rod solution, I came across something that probably would have worked better. These brackets are used on common office desks, among other things. They are cheap and easy to install. If I were to start the project over, I would have used them.

Step 8: Time to Paint

Wow, starting to look like a real greenhouse!

Even though it rarely rains in San Diego, and even though I was using moisture resistant redwood for most of my wood, I knew it would be beneficial to treat the exterior wood to increase its lifespan.

I thought about painting it white so it blended in with my truck a little bit better. But then I thought, it's going to be ostentatious enough as it is, I might as well make it stand out a little more. So I chose a nice bright green.

I wasn't looking for a glass-smooth finish, but I still did a quick light sanding to start.

Next, I caulked some of the joints in the roof. I'm not really sure why. I was thinking it would help insulate the interior and make better temperature control... never mind that there were windows on all sides...

Then I primed. I actually did 2 coats of primer, which probably wasn't necessary. Then I did 2 coats of exterior green paint. I'd never really painted anything before, and I wanted it to come out looking professional, so I bought some expensive paint brushes.

For whatever reason, when I used my fancy Purdy paintbrushes, the paint streaked like crazy. I'm sure there was something to be desired in my technique, but ultimately I went with foam brushes and the finish came out much more consistent.

Paint is good. A finish is better!

I was under the impression that paint was as good as a finish. Paint offers a fair amount of protection, assuming you get good coverage. But if I were to do it again I'd probably take a little time to add a light polyurethane finish for added protection on top of the paint.

After it was all painted, I reattached the plexiglas and all the hardware and did a test fit in the truck bed.

Step 9: Cut and Install Plexiglas

Plexiglas is very impact resistant. It may crack here and there, but it is highly unlikely to shatter. This is important if I'm going to be driving at high speeds.

A large portion of the budget went toward plexiglas. In part because it's not really that cheap to begin with. And also because I screwed up a few times.

Some of the sheets I got cut at the store. Others I bought a plexiglas knife for, then scored and cut myself.

I cut sheets for the 3 windows, a large sheet for the tailgate end of the planter bed, and then 2 very large sheets for the greenhouse roof.

Then I predrilled all of my holes and screwed the heck out of it.

I actually did all of this before painting.

Notes about cutting plexiglas:

Plexiglas is pretty easy to cut. You can do it with a razor, or you can do it with a specialized, cheap plexiglas cutting tool (which is basically just a razor anyway). The idea is to score as straight a line as you can, and then re-score it several times. You want to get a considerable distance through the plexiglas. Once you've got a good groove in place, just like a piece of drywall, you should be able to just snap it.

Getting the plexiglas scored deeply enough is critical. Otherwise you're going to end up with a puzzle-piece looking bit of plexiglas and you'll have to get a new sheet. I learned this the hard way.

Also, it's best if you keep the protective film on the plexiglas until you are finished with the project. It may not look like much, but the thin film actually does a great job of keeping your plexiglas from getting scratched. When you're finished you can just peel the film right off.

Notes about drilling through, and fastening plexiglas:

Plexiglas is great about direct impacts. Where it's weak is in horizontal torque. When attaching it, I had to drill 2 separate pilot holes. Depending on the size of screw you use, drill a normal pilot hole through the plexiglas and into the wood. Then, with a drill bit larger than the screw you're going to use, expand the hole in the plexiglas.

Use flat screws with washers!! The screw itself should be holding the plexiglas into the wood, but the threads of the screw should not be contacting the plexiglas itself. If the pilot hole for your screw is too small, the screw will grip the plexiglas and twist, causing cracking.

I was very careful with this, and even still a few of my holes cracked. I wasn't very concerned because it was fastened in so many other places. The cracks were not very visible, and ultimately the screws still served their purpose in securing it.

Step 10: Fit & Fill

Ever since I built the truck bed base, I hadn't tried fitting the whole thing into the truck. I didn't know if it would be too tall to get in or out of my garage. I didn't know if it would fit ok in the truck at all. I probably should have done this, but I didn't.

Now that I was here, though, I was happy to find that it fit PERFECTLY.

With the tailgate open, the frame kept the garden from wobbling and was quite secure without being mechanically fastened in any way to the truck itself.

With the tailgate closed, it was as if it were a part of the truck itself. I wasn't worried at all about it budging. But I still didn't have great confidence in how the top of the garden would hold out in high speed winds on the freeway...

Whatever... moving on!

What should you use as your planting media?

Here's where there's bound to be a lot of debate. Long story short, I didn't make a smart choice. I underestimated how heavy wet, saturated soil is. It still worked fine, but I'm sure my truck was screaming under the load.

I was concerned about drainage, so I used a base layer of perlite and vermiculite. These aren't always easy to find in bulk, and you'll come out of pocket a fair amount of money if you buy the bagged stuff from Blue or Orange stores. I can't recall how much of each I got, but I tried for a 50/50 mix.

I threw it into a large tarp on my garage floor and mixed them up to an even distribution. Then I tediously shoveled it into the truck bed. This layer was fairly light and I was satisfied for the most part.

The design of the garden bed worked great. It had a natural slope to it, and also had a very short incline at the very end of the bed which kept any of the media from falling out the back. The plexiglas on the tailgate held up perfectly fine against the weight.

For the remainder of the bed, I used a standard soil/compost mix. This was my bigger mistake. The total weight of this planting material, when saturated with water, was probably over 1,500 pounds. Not great on my suspension.

If I had the resources and money to do it again, I would probably advise using a lighter weight material like LECA (lightweight expanded clay aggregate). That's the stuff you usually see in hydroponics. Now, it's not LIGHT, but it's certainly lighter than straight soil.

Once the soil is in and the tailgate is closed, the Truck Farm is effectively operational!

Step 11: Add Plants

The best advice I can give for plant selection is to understand your limitations in a truck farm. Space is limited in all 3 dimensions. Vining or bushy plants are probably not the best candidates, as I found.

A lot of time, the space requirements listed on the backs of seed packets or for plant spacing. They aren't necessarily indicative of how much space the mature plant will occupy above ground.

I chose several varieties of plants that would thrive for a short period of time and then have to get pulled due to space limitations.

Toward the cab of the truck, where there would be more support, I planted some sugar snap peas on a simple trellis and some small tomatoes.

Elsewhere I planted several lettuces, kale, spinach and some jalapeno plants. Toward the tailgate end, where I knew the soil was a bit deeper, I planted a cucumber plant. And down the center were some broccoli and cauliflower.

Throughout I planted marigolds in the hopes of controlling pests, and because they added some color and character.

Some of these I planted from seed and others I used seedlings. There was no rhyme or reason to this choice, it is just what I happened to buy.

I used a square foot gardening methodology because of my limited space, but you could do row crops as well.

Step 12: Tech Hacks - Watering and Ventilation

For a while I drove around with the basic truck farm.

It held up great on the freeway. Actually way better than expected.

I got lots of questions, compliments and interest. Kids in particular loved walking up to it in the parking lot. On occasion I would be there to lower the tailgate and let them look at the layers of soil and roots of the plants. I got this idea that I would quit my job and travel SoCal teaching kids about gardening. That never happened... maybe you can do it :)

One of my goals was to have some kind of automated watering and ventilation system. It wasn't particularly necessary because it was such a small space to begin with, and watering it only took a couple of minutes. Nevertheless, I wanted to keep learning.

My idea was to have a small water reservoir installed on the side of the garden, connected to solar powered pump and a basic drip system. The reservoir would use a simple float valve/switch to automatically shut off the pump. And then I would have moisture sensors in the soil to trigger the watering cycle.

Keeping it manly... with ammo cans

I had some ammo clans left over from this and that. It just so happened that they fit perfectly into the small space on the sides of the garden. I knew ammo cans held up somewhat well to water, and they were cheap enough to replace in the long run.

My solution was pretty ugly, and more of a hack, but it was functional.

First ammo can: I used one ammo can as a battery box for a small DC battery. In hindsight, I should have used a deep cycle battery, but I had the SLA battery on hand and figured if I could just keep it dry, it would suffice. I built a small wood frame for the battery inside the ammo can, and also fit inside the Arduino and breadboard.
Second ammo can: The second ammo can was strictly for use as a water reservoir and to house the pump. I linked it to the first ammo can with a cheap brass nozzle and some flexible poly tubing. Make sure the pump you use has enough power (large enough head) to pump the water high enough to reach your garden soil. Mine I think was a 9" head, which was more than enough. Also, A/C pumps tend to be cheaper than D/C, so I bought an A/C pump and then a cheap AC/DC inverter.
Third ammo can: In the third ammo can, I put a toilet float, attached to a long rod, and hooked up to a manual switch. I don't have a part number for the switch I used, but really any similar pressure switch will work. I sealed the !@#$ out of it with silicone.
Random tupperware: I needed a place to physically house my pump and inverter, so I threw them into a rubbermaid tupperware and linked them with more poly tubing to the water reservoirs. This was inelegant, but it was all tucked away on the side of the truck bed anyway.

The concept was similar to a toilet bowl tank. When the Arduino triggered the pump, it would start pumping until the float valve got low enough to toggle the switch, telling the Arduino to stop the pump. The Arduino would trigger the pump automatically either on a timer, when soil moisture was too low, or manually with a button on the shield.

I never got around to programming the moisture sensor, but it was still somewhat automated in the sense that I could just fill my ammo cans and push a button and it would water.

I no longer have my Arduino solutions for this, but if I could figure it out with zero background I'm sure you can as well. I will say that I used an Arduino Uno with a Relay Shield, a simple breadboard initially, and a starter set of jumper wires. It was all low current stuff, so nothing really heavy duty was required. Ultimately I bought some soldering equipment and learned how to solder, and got rid of the breadboard.

I added a LED to the Arduino so I could have a visual indicator of when it was attempting to water. I drilled a hole in the ammo can so I could see the LED.

Powering the system

As I said before, I had a sealed lead acid battery which I hooked up to a few solar panels and a solar charger/regulator. I used two cheap 5W and a 15W solar panel, which I screwed to some strong neodymium magnets. I then attached the magnets to the top of my truck's roof and wired the panels to my battery box and Arduino.

The battery was then wired to an AC/DC inverter, which was used to power my AC pump.

While I was at it, I bought some cheap, low power CPU case fans. I hooked them up to a temperature and humidity sensor, which I programmed with the Arduino to trigger under certain circumstances. The programming for this is relatively simple. The fans were DC fans, so they were not required to be hooked up to the inverter.

The temperature and humidity sensors produced an analog output which could be easily read by the Arduino. At whatever level you like, you can trigger a response from the Arduino. This is not a programming Instructable because it's beyond my scope, and even though I did it, it's almost certainly beyond my expertise to teach.

I used a very fine blade jigsaw to cut holes in the plexiglas. Despite this, it caught several times, causing some unfortunate cracks. The fans installed just fine, but it didn't look as elegant due to the cracks.

The system worked perfectly. What was also great, was that while driving, wind would automatically get drawn through the interior, whether the fans were turned on or not, and cause natural ventilation. Unfortunately I don't have any videos of the actual watering process in action.

It was all very low power consumption, and since I only watered about once a week or so, I never got close to draining the battery.

Step 13: We Are Expanding...

Remember when I said to choose your plants wisely?

Turns out sugar snap peas can grow several feet high... certainly higher than the 24" of vertical space I gave them.

I decided to cut a couple holes into the plexiglas top of the greenhouse. I framed them pine moulding (I couldn't find redwood corner moulding) and glued them to the plexiglas. This was not very secure, and in retrospect I should have just chosen different plants.

The cutouts looked great, but the wood did not stay secured for more than a month or so. Also having a large cutout in the middle of the plexiglas probably took away from its ability to stabilize the greenhouse a bit, and added a point of wind resistance while driving.

The snap peas did end up growing out the top, and they even survived at freeway speeds for a time. Sorry to anyone on the I-5 South that I may have pelted with sugar snap peas.

Step 14: Reap the Rewards

The greenhouse was a great success.

I had several good harvests. I also had a few disappointments, which either succumbed to disease or had to be pulled due to space issues.

At one point I bought a few thousand ladybugs to lay waste to an aphid infestation I had. I built a small ladybug house for them, which I mounted inside the greenhouse using additional magnets. The ladybugs are savage killers it turns out. Following their night of aphid slaughter, they engaged in a large ladybug orgy before departing my truck farm. Some of them hung out for about a week (which is pretty impressive considering I had them doing 75 on the freeway for much of that time), but ultimately they all took off. At least my aphid problem was solved.

I was able to grow for almost two full planting seasons, but ultimately retired the project when I sold my truck. The garden was far too heavy to be used on a daily commuter. What money we saved in produce was easily overcome by the added expense in gas.

The experience of learning some basic woodworking, programming, gardening and electronics was invaluable to me. I was also able to share it with a lot of interested people. Even though I never realized the idea of making it into an official business of some sort, I'm glad that so many people got enjoyment out of it.

I even had people ask about starting a coop, or creating a fleet. They might have been making fun of me :)

Step 15: Lessons Learned

I achieved just about all of my original goals with this project. I bought some add-a-leaf springs for my truck to help its suspension a bit, and otherwise the truck was not negatively affected at all. The bed and liner were in perfect shape when I finally removed the Truck Farm from the bed. In large part, I feel this was because I had taken care to separate the wet soil from the truck itself with a physical barrier.

If you're interested in trying this, here are a few suggestions:

Choose your growing media wisely. Find something lightweight that drains well and you may be able to forgo other expensive items like the drainage mat.
Choose plants wisely based on available space. It's very disappointing to have to kill a plant that is otherwise healthy, because you made a bad choice on what to plant in the first place.
Unless you're interested in learning Arduino and all that other fun stuff, keep it simple. Such a small raised bed takes only a few minutes to water. An automated drip system is not necessary. Adequate ventilation is important, but again for such a small space, you probably don't need fans.
Design your structure with care. I got lucky that my whole structure stayed together. I know more about woodworking now and realize how flimsy the whole thing really was. I could have made the structure much more stable while using considerable less wood in some areas.
Take care of your wood. Take the time to properly treat and seal exposed wood framing. I painted as much as I could, but even so, the wood ultimately rotted within 2 years. Even having rotted, the greenhouse stayed put together, but once I removed it from the truck to sell the truck, it became evident that it wasn't very stable anymore.
Enjoy the process. Many of my projects end in abject failure, or they are constant works in progress. Few are outright successes. The true success comes from the experience and the knowledge gained during the process.

Believe it or not, I am not the only Truck Farm. In fact, as I discovered after I had originally thought of the idea, there was a group of guys that made a small film/documentary about their own truck farm. I used their design as a foundation/basis for my own, but otherwise it is all original work. I even came up with the idea on my own, and just so happened to discover their awesome project afterward. This lends some credibility to the idea, at least, that multiple people, separated by many miles, came up with a very similar idea.

I hope you have success if you try it, or maybe at least get some fun ideas from it.

This project also served as a gateway to my interest in homesteading. Because of my successes, I used some of the lessons learned to build a healthy, huge raised bed in my back yard from cinder blocks. I also wrote an Instructable on that, which you can view here: Build a Concrete Block Garden!

Thanks for reading!