Intro: Ultimate Auto-Wicking Garden
Unsatisfied with a simple raised bed garden for the backyard, we decided (or I should say I convinced my wife) on a wicking bed garden with a twist... an auto-refilling raised bed wicking garden (try saying that three times fast).
The design utilized the float ball valve from a toilet bowl and passive pressure from our rain barrel to constantly and consistently water our vegetable garden while we enjoy the fruits of our labor (no pun intended). The design uses the basic tenets of wicking gardens, which provide water from underneath the soil to efficiently water the garden while encouraging deeper root growth and less evaporation. Another benefit to the design is that it is easily adaptable to greenhousing in the colder months or fencing out those hungry squirrels!
Step 1: Supplies and Tools
You can spend as much or as little on supplies as you like, depending on how creative and resourceful you are. We decided to go the pricey route and buy everything new to reduce our build time and ensure that everything touching our food is safe. You can, however, source the wood from old fence posts and the soil and rocks from Craigslist. The plastic components require some more searching but the liner can be sourced from old tarps or pool liners, the bucket from a large kitchen/restaurant and the float valve from an old toilet.
The prices are approximate (USD) and specific for our build (13' x 6' x 1.5'):
• (15) 1.25" x 6" x 8' Pressure Treated Lumber, $6.50 ea. = $97.50
• (3) 1" x 1" x 8' Pressure Treated Lumber, $2 ea. = $6
• (2) Cubic Yards of Organic Top Soil Delivered, $180
• (1) Cubic Yard of River Rocks Delivered, $100
• (1) 10' x 25' Polyethylene Sheet, $10
• (5) 4" x 10' Corrugated HDPE Irrigation Pipe, $6 ea. = $30
• (1) Corrugated to Downspout Barb, $4
• (1) 4" Corrugated Pipe End Cap, $1.50
• (1) 5 Gallon Bucket, $2.50
• (1) Bucket Lid, $1.25
• (1) Float Valve (I used this one to save space, click here), $6.50
• (1) 15' Garden Hose, $8
• (1) 4" Section of Any Diameter Tubing, $0.50
• (1) Roll of Landscaping Fabric, $10
• (2) 1lb. Box of #8 x 1-1/4" Deck Screws, $7 ea. = $14
• (4) Zip Ties, $0.50
• (1) Silicone Sealing Tape, $7
• (1) Teflon Tape, $1
• (1) 3/4" Barb x 3/4" Barb PVC Coupling, $0.75
• (1) 3/4" Hose Clamp, $0.25
• (1) 5/8" Inner Diameter PVC Hose, $0.50
• (1) 1/2" MNPT x Barb 90 Degree Elbow, $0.50
• (1) 10' x 1" PVC Pipe, $3.50
• (4) 10' x 1/2" PVC Pipe, $2 ea. = $8
• (16) Pipe Brackets, $0.10 ea. = $1.50
• (32) 1/2" Stainless Steel Screws
• Drill & Drill Bits
• Miter or Circular Saw
• Carpenter's Level
• Rotary Tool
• Staple Gun
• Pipe Cutter
• Razor Knife
• Garden Rake
Step 2: Building the Box
This step will obviously vary with your application and size, but the first thing you want to do is determine the location and the size of the box. Once you have the size planned out determine your materials and cuts. From the research I've done, wicking boxes should be in the range of 8 to 18 inches deep. The soil will only wick water up about a foot, depending upon its composition, however if you have larger plants with deeper roots you can go as deep as 2 feet.
Our box will have a myriad of plants inside, with varying root depths, so we chose a soil depth of 12 inches with a reservoir of 6 inches. That means we need 18 inches vertically, which is the height of three boards.
Our box is also a bit wider than what is optimal, at 6 feet wide, but since I didn't want to build multiple valve assemblies for two parallel beds we decided upon a 13 by 6 foot bed.
With the size specified we envisioned the cuts needed and planned out the amount of wood required. Vertical supports would also be needed approximately every 3 feet to prevent the wood from bowing out and to join the three tiers of boards. Therefore we ended up needing (15) 1.25" x 6" x 8' and (3) 1" x 1" x 8' pieces of pressure treated lumber.
Cutting six of the 1.25" x 6" into 5 foot pieces, we butt them up against six 8 foot pieces creating the two 13 foot sides required by the design. The remaining six pieces of 3 foot overcut (from the 8 foot lumber in the last sentence) was paired up with three additional 6 foot cuts to produce the two 6 foot sides. All of these were joined with seven 1.5 foot cuts of 1" x 1" on the long sides (see the picture) and two 1.5 foot cuts of 1" x 1" on the short side with deck screws. Pilot holes were drilled prior to screwing everything together to prevent splitting the wood.
Once the sides were individually assembled we moved everything onto a level surface to assemble the box. The short sides were then butted up against the long sides at 90 degree angles, drilled, then screwed using the end 1" x 1" supports on the long side.
Step 3: Preparing the Plot
Once your box is built use it to block off the area you want it to go. If the ground is flat and level there is no need to clear out the existing terrain, but in any case you will need to counter sink the bottom of the box into the ground so that nothing comes out of the bottom of the box.
Start by placing the box where you want it to go (an extra pair of hands is helpful) and use it to either chalk out the perimeter or use a flat head shovel to trowel out the perimeter using vertical digs. Once the perimeter has been traced, move the box out of the way and either finish the trowel by removing a couple of inches along the inside of the perimeter (if you plan to just counter sink the box) or all the sod within the perimeter (as seen in the pictures). If you are removing all the sod, as we are in the pictures, do it by squaring off small sections with vertical digs then removing those sections with shallow horizontal digs. The sod should come up as whole pieces, roots and all, which I used to re-sod some areas of my lawn that were looking a little bare.
Once the sod is all removed, use a garden rake to smooth out the soil and screen any large stones that may puncture your plastic liner. A board and carpenter's level work well to make sure the soil is flat and level so that there isn't any pooling once filled with water.
Next, lower the box back into position and line the bottom with corrugated cardboard (with no color print). This will provide some biodegradable protection while you finish up the rest of the project.
Note: Refer to the step regarding the Valve Assembly, preparing a trench for the water supply line at this point is much easier than waiting until later in the project.
Step 4: Mounting the Pole Holders
If you chose to put an animal screen around your garden or if you want to greenhouse with it, you will need to install poles to support the screening and/or plastic. This method is a simple, quick, flexible and inexpensive way to do it.
First, start out by cutting your 1" PVC pipe into 12" sections with a hacksaw or pipe cutter. You will need a pair of holders for every 3 feet or so of box length, so I ended up cutting 8 and spacing them evenly, 4 per long side. Using two pipe brackets per holder, I used the 1/2" stainless steal screws to mount the cut pole holders. To make things a little easier for myself later on, I also screwed a single screw into the bottom of each cut pole holder, about 1/2" from the end to prevent the pole from coming out of the bottom of the holder.
Since all boxes will differ in shape, application and size, PVC pipes offer a great modular alternative to a static fence or structure. They can be joined together or just bent to create tunnels or boxes of various sizes to drape screening or plastic over, or they can be used in a more functional manner to incorporate mister pipes, grow light electrical conduit or a support to train vines and bines up.
Step 5: Lining the Box
Alright, now it's starting to look like something! Take a minute to admire your handiwork (or curse yourself for not measuring twice before cutting). You're basically halfway there and most of the hard work is done... oh except for shoveling a few tons of rocks and soil that is!
The basic idea when lining the box is to provide yourself a lot of slack with the liner. I used a fairly thin 3-4 mil liner, ideally you want to go a little thicker, but it is important to allow at least a foot in each dimension for overhang. I started in the middle of one of the short sides by tacking the middle of the liner with some plastic backing squares. The backing squares will provide added support so that the staples do not tear the liner and you can cut these out of any food-grade plastic container. You can also provide a little extra tear-resistance by doubling the liner over at the ends that you are tacking.
If rule one of lining the box is leaving some slack in the liner, rule two is to obviously not tear the liner! But I'm sure you figured that part out by now.
Unfurl the rest of the liner and place it loosely in the box, tacking every foot or two with a staple, less is more right now because you may need to remove them later (I did). Now you'll want to add some weight around the inside perimeter of the box to weigh the liner down, you can do this with bricks or the rocks you plan to use in the later steps of this instructable. Once you weigh down the inside perimeter you can adjust your liner as needed so that no area is under stress or stretching (this is where that extra slack comes in handy).
Now you can work your way slowly around the box perimeter, doing about ten staples at a time every 6 inches or where needed, then doing the same on the opposite side. Remember to use a backer every time and try to wait until the last possible moment to trim the remaining liner.
Step 6: The Reservoir
Here's the step that separates wicking gardens from raised bed gardens, the water reservoir.
The reservoir functions exactly like the name infers, as a supply of water for the soil above. The design of this reservoir isn't too revolutionary, it consists of coiled irrigation tube and river rocks. However, whereas other wicking bed garden reservoirs are replenished by a vertical tubes, this one will incorporate a valve assembly housed in a bucket to ensure a constant and reliable water supply.
Once the box is lined, it is time to install the reservoir. I elected to have a 6" high reservoir, which allows for a 5" diameter irrigation tube to distribute the water and river rocks to support the soil above and allow the water to dissipate across the entire garden bed. The rocks make it so that the soil isn't seeping in water, which can be detrimental to plant roots and cause proliferation of harmful bacteria and fungus. River rocks are not your only option here, they just happen to be plentiful and cheep for me due to my proximity to the Delaware River, I have seen others use shells, nut husks and lava rocks (pumice) just as successfully.
Working from the outside in I formed a perimeter of rocks then coiled in the tube. There's no standard length of irrigation tubing to use, but I found that a length of approximately twice the perimeter worked well (about 50 feet). In the pictures you can see that I used some of the rocks as a weight to hold the tube in place to prevent it from popping out from the torsion of being coiled, once all the rocks and tubing is in place these can be evened out. Luckily each of the boards of the box are 6" high so I just piled the rocks up to the edge of the botom board.
You will also need to know the volume (cubic dimension) of rocks to get. This can be done using the following formula where (l), (w) and (hr) represents the length and width of the box and the height of the rocks in feet, respectively, and (lt) and (rt) are the length and radius (half the diameter) of the tubing in feet, respectively.
[ (l) (w) (hr) ] - [ (lt) (rt)2 (π) ]
To convert it to cubic yards divide it by 27 (27 ft3 = 1 yd3).
For my application, I ended up needing approximately 0.9 cubic yards so I just ordered a full cubic yard and used the rest around my property.
Note: You will need to proceed to the next step before filling in the entire reservoir with rocks.
Step 7: The Valve Assembly
So here's where the magic happens. By installing a valve assembly we have transformed what would be an ordinary wicking garden into a semi-autonomous vegetable producing machine! Or something like that.
When you near the spot you want your valve assembly to go when creating the reservoir (see last step), you will want to make provisions for your valve. The spot should be easily accessible to your water source and near to the edge of the box to make running the line simpler. If you plan ahead, you can even do most of this work before even placing the box, making this step go much simpler. I will divide this step into two substeps, one for making the assembly another for installing it, both parts are easy when done right.
Building the Valve Assembly
To build the valve assembly, all you need is a hose long enough to reach your water source, a 5 gallon bucket, lid and a cheap toilet float valve that fits in the bucket (see supplies list for the model I used).
Take your rotary tool or drill with appropriate sized drill bit and create a hole in the bottom of the bucket towards the center that will allow the base of the float valve to protrude through (the threaded part that hooks up to the water supply). Use the supplied rubber gasket and plastic nut to secure the valve inside the bucket, it doesn't need to be watertight as long as it stands upright. Now test fit the water inlet by putting together the tube fittings and barbs as illustrated in the pictures. These need to be watertight but they will only be under moderate pressure, so use teflon tape around the threads and I used silicone sealing tape as an added precaution around the fitting. You can test the connection by connecting the hose to a water source and letting the bucket fill with water (CAUTION: home water supply lines may provide too much pressure, use carefully). Empty and adjust the valvle fill line until it stops filling 6" from the bottom of the bucket.
After emptying and drying your bucket, measure 6" up from the base of the bucket and cut a hole with your rotary tool or razor knife to match the "downspout' end of the Corrugated to Downspout Barb. I traced out a template to use, but that isn't necessary since it doesn't need to be watertight, just snug so the irrigation hose doesn't fall out. Finish everything off by drilling a few air holes in the lid, a layer of garden fabric between the lid and bucket will prevent mosquitoes and other insects from getting in.
Installing the Valve Assembly
Now that you have it built, it's time to put it in the box!
If you haven't done so already, prepare a trench for the water supply line (see note in the step Preparing the Plot) that goes under the edge of the box and provides enough clearance underneath the liner so the hose doesn't kink. This is best done before lowering the finished box onto the prepared plot, just be sure to not cover it up when placing the cardboard down.
Push the hose through the trench, underneath the box side until you see it poke the bottom of the liner. Create a small slit in the liner and push the hose through until you reach the area where you want to place the valve assembly. Pull some slack up in the liner and create a small collar around the hose with the liner and secure it with a zip tie, you can wrap it with duct tape for added leak protection. Connect the free end of the hose to the bottom of your valve assembly, put it into place, attach the irrigation hose (you may need to cut the bell end off to fit the barb, as in the picture), and finish filling in the rocks.
So you ask, why not install the valve assembly first, then do all the rocks at once? Well the rocks provide enough shift in the liner that by the time you fill in the reservoir everything may have shifted. But if your box is small enough or if you are feeling lucky enough, I guess you could install the valve assembly without filling in with the rocks.
Step 8: The Water-Permeable Barrier & Drain
Here's the short but important step to create physical separation between your reservoir and soil. This water-permeable separation allows water to wick up through while preventing the soil from gunking up the works. Also during this step we install a drain which will remove excess water so that you don't end up with a muddy swimming pool.
Drill a hole just above your desired water line large enough to fit a small length of hose into it; I had my hose left over from another project so I just trimmed a few inches of that. Push the hose through from the inside and run it through the liner just as you did in the previous step. Take a small square of gardening fabric and secure it to the outside end of the tube with a zip tie to prevent any insects from getting inside and clogging it up. This will serve as your drain just in case it rains more than what the reservoir is designed to handle.
We actually got to test the drain just a few days after finishing the project when the remnants of a tropical storm came through and dumped a few inches of rain!
Now cover the entire reservoir rock bed with overlapping layers of gardening fabric or water permeable weed plastic, be sure to allow for a few inches of overlap along the perimeter so that soil doesn't work its way down the side of the box.
Step 9: Filling With Soil
There are several soil types and amenities to consider when filling the box with soil. Our application involved an organic top soil mixture amended with compost from our compost bin, bone meal, and blood mean. Although important, I will not cover soil types and amenities in this instructable due to length and number of options.
Filling the box with soil is equal parts sweat, ingenuity and teamwork. We found it easiest to shovel in the first ten wheelbarrows full of soil into the box, using it to pack up against the perimeter of the box to hold the gardening fabric in place. We then formed a crude ramp out of scrap boards and a milk crate and poured the rest into the box. A system was soon established where one of us would fill the wheelbarrow while the other moved the ramp to the next location while spreading out the soil with a shovel and garden rake. For our application we needed about 3 cubic yards of soil, you can determine the volume of soil using the following equation:
[ (l) (w) (hs) ]
Take the length of the box in feet (l) and multiply it by the width of the box in feet (w) then by the height of the soil (hs). Just like before, you can convert it to cubic yards by dividing it by 27 (27 ft3 = 1 yd3).
Step 10: The Finishing Touches
Now that your box is all filled with soil, all that's left to do is to hook up your rain barrel and enclose the garden if you chose to do so.
For us, hooking up the rain barrel was as simple as screwing the hose running from the valve assembly into the spigot for the rain barrel. Other setups may be different and require barbs or other connectors. If your roots end up needing a bit less water this setup is also ideal because you can turn the water off at any time.
Finally, install your 1/2" PVC pipe into the pipe holders by placing one end in the nearest pipe holder and bending the opposite end into the parallel pipe holder on the other side. As your plants grow you can augment the design by adding additional lengths of pipe or wood poles joined with connectors. Then just measure and cut the appropriate length of screen or plastic and drape it over your PVC structure. You can secure it to the frame with large binder clips but if you need a more permanent solution you can use tacks or staples.
Now your semi-automated raised bed wicking garden is finished and ready to be planted! You'll be able to spend less time worrying about watering your vegetables and more time enjoying them. An added benefit is that on top of a house sitter, dog sitter and baby sitter, you won't need a plant sitter when heading off on your summer vacation.