Introduction: Ultimate Auto-Wicking Garden

Picture of 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

Picture of 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
• Scissors
• Pipe Cutter
• Razor Knife
• Wheelbarrow
• Shovel
• Garden Rake

Step 2: Building the Box

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.


Stif (author)2016-06-08

Is there any reason I wouldn't want to substitute a soaker hose for the corrugated drainage pipe? Seems like it would be less work to incorporate and I wouldn't have to have so much extra volume of "resevoir" in the rock bed?

Great idea, love the set it and forget aspect of this instructable-

thanks for sharing!

zymurgeneticist (author)Stif2016-06-08

Thanks for the comment Stif and for the soaker hose idea.

Honestly I don't know how that would work out. Do soaker hoses need a certain pressure to pass the water through? I know that they are typically hooked up to house spigots which carry more pressure than this passive system.

Theoretically, you don't even need the drainage hose, you can have it drain directly into the rock bed if you like, it'll just be a little more expensive and I'm not sure it'll improve the system. Happy experimenting either way!

RayJN (author)2016-05-23

I know it would cost much more but much tougher, how about roll on truck bed liner?

zymurgeneticist (author)RayJN2016-05-25

I'd imagine you could use whatever holds water as long as it's food-safe (which I would be concerned about with a roll-on truck liner). The pond liner that many have mentioned is a good, durable, alternative.

jtmcdole (author)2016-05-22

I've built a number of my own wicking bed gardens - the auto filler is an awesome idea!

zymurgeneticist (author)jtmcdole2016-05-25

Thanks jtmcdole, it's a lifesaver when I'm out of town!

1MichaelWheeler made it! (author)2016-03-13

Awesom project! Just got mine finished.
I had a bunch of very large sheets of sturdy glass left over from a previous project that I used as the bottom weed barrier (don't think it gets much better than that).

I used some thick shower barrier PVC sheeting from home depo to cut strips from and lined around the top of the bed, stapling the plastic and water barrier together. I think it worked out great!

For the wood, I ended up using large 2" thick boards. Bottom is a 12" wide board, and the top is 6" wide. Bed is 12' x 6'. Because the boards came in those sizes, my only joints are on the corners.

Getting the rock around the 4" pipe and getting it in position was probably the hardest part.

My biggest recommendation; get the thickest plastic you can to lay in the bottom. I think I may have a tiny leak in that plastic...

Over all, I am very pleased.

If you are concerned about the plastic, try pond liner. Get it at an end-of-season sale and you will be worry free! Also get some extra - it has 1,001 uses, outside and in the house.

Wow! It looks beautiful Michael, congratulations! I think you'll have a beautiful harvest, definitely post pictures once all the plants are established!

jorgeisagirl (author)2016-05-22


EssyC (author)2016-05-22

Brilliant idea, I will definately be looking into this.

steveholt (author)EssyC2016-05-22

i will definitely

1MichaelWheeler (author)2016-03-08

When you adjust your float valve, how much water/soil saturation do you aim to maintain? 1 inch? Also, I am building this, and am curious about how well the water wicks all the way up to the shallow rooted plants. Would you speak to your experience on this? How deep is your dirt from the weed barrier?

Hi Michael. The float valve (and thus the water line) is adjusted to be approximately at the level of the gardening fabric. You will naturally have overlap because the rocks/pipe create irregularities that will dip and allow wicking to happen. You shouldn't place the water line above this, however.

Water will wick differently for different soil types; water will wick farther the more organic matter in your soil. Our experience was that it wicked fine up through 11 of the 12 inches of soil we had in the bed, the last inch was likely a combination of wicking distance and evaporation. That said, we had no issues with shallow rooted plants drying out.

EricaE9 (author)2016-02-28

I'm ready to start planting! Question: Will seeds germinate through the wicking action or do I need to top water until they sprout? At what point in plant maturation can I stop to watering and let the wicking bed do its thing? Also, have you found any plants that aren't amenable to this type of gardening? Thanks!

zymurgeneticist (author)EricaE92016-02-29

Hi Erica, I'm happy to hear you're gardening!

You're going to want to follow the directions on your seed packets. We've sown peas and some greens directly, though it's always a good idea to water them until they're established and their roots can reach the water below (which will depend on your soil type and depth).

I haven't found any plants that are not amenable to a wicking garden, though it would stand to reason that fruit trees are a no-no as well as any plant that needs special soil conditions. I think most of your vegetables, however, will like this setup just fine.

EricaE9 (author)2016-02-28

I'm ready to start planting! Question: Will seeds germinate through the wicking action or do I need to top water until they sprout? At what point in plant maturation can I stop to watering and let the wicking bed do its thing? Also, have you found any plants that aren't amenable to this type of gardening? Thanks!

1MichaelWheeler (author)2016-02-14

Awesome project; I have a couple questions. Do you have any issues with the roots going down and poking holes in the water barrier?

As you keep a sheet of plastic between the pressure treated wood and the soil, I imagine the plastic rots and gets brittle over time? have you had to replace that plastic?

Do you have any issues with standing water. Such as sludge collecting in that bucket and valve?

Curious about these things as you maintain this bed over time...

Thanks Michael! To answer your questions...

The roots don't really poke through, they more or less divert themselves. I'm thinking that was anticipated by the designers of the water barrier.

I'm sure that eventually the plastic will become brittle and need to be replaced, however it hasn't happened yet. The plastic becomes brittle primarily by exposure to UV light, since most of it is covered, exposure is minimal. You can mitigate the rest of the exposure by capping your wood with a little shelf.

I've only ever had issues with standing water once and it was because the drain hose cap accumulated silt. I simply took the cap off, scraped it out, and it was fine. Took me about 10 seconds to fix.

KaneNOS (author)2015-11-17

Awesome dude!

caine2003 (author)2015-07-04

Have you thought of adding red worms to your soil? I'm trying to come up with a list of pros and cons of doing it to mine, and any help would be appreciated.

Good question caine2003, I haven't. The main reason being is that I have a ton of them in my compost bin, which is the same compost I add at the beginning of every growing season. You could always experiment with a worm tower ( and see how that works for you.

caine2003 made it! (author)2015-03-28

If anything, the plants wont drown like on the rest of the property.

Looking good caine2003! We're planting our spring greens this week in ours!

I'm loving your daffodils too, ours just started to grow last week.

I haven't been able to hook mine up to gutters, so I decided to test mine by hooking it directly up to the garden hose. I found I have about 3 leaks in my reservoir. If I build another one, I'm going to double or triple line the plastic just the be on the safe side.

caine2003 (author)caine20032015-07-04

This pic is from 21 June. The plants grown over the netting in the pic. There are 17 tomato plants, 3 types of onions, and 2 types of carrots growing in here. A winter squash vine has grown over to the bed, about 15' away, and has started growing up the PVC supports.

Looks like your garden is really productive, great job caine2003!

buck2217 (author)2015-07-01

Great idea for keeping stuff moist esp if you are going away for a few days

zymurgeneticist (author)buck22172015-09-02

Thanks buck2217!

Abitaro made it! (author)2015-06-28

Great project, and very fun to make.

zymurgeneticist (author)Abitaro2015-09-02

I love it! What a perfect little box!

zymurgeneticist (author)2015-05-07

I thought a little update was in order, the box weathered our unusually cold winter well and is now full of spring vegetables! We used a row cover to start the growing season early, here's a picture prior to thinking the rows.

michaelb2 (author)2015-04-06

Is there a relief valve to lower the water level in case of a large amount of rain?

Hi michaelb2, take a look at Step 8, there is an over flow tube so that it doesn't fill with water. No "valve" specifically, however you could plug it, though I don't know of any applications where you would want to.

iphlue (author)2014-10-29

Looks very much like Larry Halls rain gutter grow system. look for him on YouTube and pinterest. Facebook at rain gutter grow system group. awesome group and Larry has started a business to sell a lot of what's listed here at good prices.

zymurgeneticist (author)iphlue2014-10-30

Thanks for bringing him to my attention, I never heard of him before today but the methods do look very similar! It looks like his is an amalgamation of container gardening, wicking beds and hydroponics. Cool stuff!

RoBear613 (author)2014-05-28

Everything I have seen on wicking requires some kind of wick (cotton rags, sphagnum moss, etc) to bring the water up to the "soil" above. While you have the soil in direct contact (albeit with a water permeable membrane between) with the water reservoir, how is the water going to wick up if the level drops below the barrier? Seems to me that you will have to keep the reservoir filled in order to keep contact with the soil. Any unexpected drop in water level will stop the wicking process and depending on the time involved, result in dry soil.

Am I missing something?.

Hi RoBear613, the reservoir is automatically refilled through the float valve, hence the "auto-wicking". Once the water falls below the fill line in the bucket (which was measured in Step 7 to be the height of the reservoir) the valve lets more in. That way the soil remains in constant contact with the water.

All wicking beds of similar design (albeit most without the automatic valve) benefit from some irregularities from the medium in the reservoir layer to allow for some tolerance in the water level of the reservoir.

I'm not sure that really answers the question.

If you have a 6" deep reservoir, and allow for a 2" interface zone in the area between the reservoir and soil irregularities at the weed block, how does water get to the soil when the level drops below the interface zone? Yes, the valve will top it off back to the interface zone, but that leaves 4" of water in the reservoir that does nothing at all for the garden because it can't reach the soil in the interface zone. That final 4" would only be additional capacity for your rain barrel - not a bad thing, but not the stated objective of the project.

It seems that to get the full benefit of that reservoir, you should install wicking material the full height of the reservoir and set the refill valve to trigger when the level gets to the lowest inch or so, topping it off to the interface zone again.

If you don't want to deal with the wicking material, then reducing the height of the reservoir and eliminating the weed fabric, thus allowing the soil to mix in, will accomplish the goal of avoiding saturated soil too near the roots while efficiently using the volume of the reservoir.

That said, I built a raised, lined bed myself this spring but if I'd seen your instructible first I would have included the drain you put in to prevent flooding. That's a nice detail that didn't occur to me at the time but I will retrofit this one and include it in the next one. Thanks for that tip.

Hi balloondoggle, I'm glad you'll be able to put the drain aspect to good use, it has definitely come in handy a few times this season.

As for the rest of your comment, I guess I'm not quite sure where the issue is with the reservoir. Yes, once the water drops below this interface zone it will no longer be in contact with the soil and thus no longer wick up, but I do not see how it is in conflict with the stated objective of the project.

Without some dead space underneath there is the issue of unequal water dispersion, areas around the tubing would be the wettest while the areas farthest from the tubing may not get water at all. Remember, we are dealing with passive pressure and small volumes within the tubing, the water would effectively have to wick (seep) sideways dealing with similar impediments as wicking up. This is getting into hydraulics and the fluid mechanics of water and mud and the surrounding soil, which is more than I'd want to tackle in an I'ble, which is why it's easier to just eliminate all of that and stick with the reservoir design and not have to calculate the placement of the tubing.

By eliminating the weed fabric you will effectively have the same problem but then you will also have saturated soil near the roots because there will be nothing to stop the roots from growing into the "reservoir" and sitting in saturated soil.

By keeping the fabric but lowering the reservoir you avoid this however there is an inherent flaw in all wicking gardens using soil and that is after awhile the bottoms will fill with silt and the waterflow will be impeded (much like above). Good construction, good fabric and bulky soil will prolong this, but it will happen over time and having a lower reservoir height will hasten the silt filling the reservoir.

I see no reason why you couldn't work a wick into the design and utilize that extra 4" of reservoir though. Let me know how it goes if you give it a try.

jsmith261 (author)2014-08-05

I caution against using treated wood. This from How Stuff Works: The most common preservative used chromated copper arsenate (arsenic) but now is alkaline copper quat, or ACQ. Copper is toxic to various insects and fungi that might cause decay. ACQ binds to wood fibers very well and allows wood to last decades even when it is in contact with the ground. The chemicals in treated wood are generally not good for humans. This is why you see warnings advising you to wear gloves, avoid breathing the sawdust, and refrain from burning treated wood. Keeping small children away from treated wood is also a good idea.

I've always wanted to build a project like yours, but the wood is a problem.

Hi jsmith261, please refer to my reply to sturgess2003 below.

Excellent answer, thank you. Like I said, I've always been concerned about the wood. I appreciate the thought you've put into it. I live in Southern California where everyone's afraid of everything, but still wants food to be organic and local. I bought planting boxes and felt good about growing basil and cherry tomatoes, then had someone point out that the boxes were plastic and I shouldn't eat the food. It's hard to know how to win.

LynxSys (author)2014-07-25

This is hands-down the best raised-bed I've seen yet. The automatic rain-barrel refilling of the wicking reservoir is brilliant. I have a bunch of question, though; I hope you don't mind!

~ Have you had (or do you anticipate) any problems with the top edges of the HDPE sheeting tearing or disintegrating with UV exposure? (Is it UV resistant?)

~ What type of landscape fabric did you use?

~ Do you see any reason not to fit the drain into the reservoir bucket directly?

~ What water-level have you found to be ideal? it looks like you're trying to keep the water line an inch or two above the top of the rocks. Is that right?

zymurgeneticist (author)LynxSys2014-08-01

Hi LynxSys, thanks for the compliment! Hopefully these answers are what you're looking for:

- I haven't had any issues yet, but am aware of the photosensitivity of HDPE. Right now the top edges don't get a lot of direct sunlight because the sides, soil or plants block it out. As I mentioned below, I may add a shelf to the top edge of the wood which should shade the plastic completely.

- I don't remember the name of the fabric per se, it's a perforated plastic sheet though, not the woven or pressed felt type. Does it matter??? I'm not sure, from the other wicking garden designs I've seen it doesn't seem to, but maybe another reader could chime in on that.

- I see no reason not to fit the drain directly off hand, though you would be dealing with back flow. Not that I think that would matter.

- The water level is actually right in line with the top of the rocks, if not a little lower. You don't want to go over the rocks too much or else the soil will just remain constantly saturated, which depending on your design/depth may end up a bit messy or resulting in root rot.

LynxSys (author)zymurgeneticist2014-08-04

Hi zymurgeneticist,

Thanks for your thorough answers! It seems like you did a lot of excellent research in deciding on materials and methods for this project, so I appreciate your taking the time to explain all of your hard work to the rest of us.

I did a little more research about UV-stabilized sheeting, and I thought I'd share my findings. It turns out that UV-stable polyethylene sheeting is sold as pond liners for water-features in gardens. Although it is "fish safe", I seriously doubt that it's USDA "food grade". I don't know how much that would matter in practice, but you and I both seem to be the cautious types when it comes to our food, so I'd be disinclined to try it. I haven't been able to find any sources of UV-stabilized, food grade plastic sheeting (although maybe I'm not looking in the right places; if anyone else here knows something that I don't, please speak up!).

I asked about this in the first place because I've seen some regular ("UV-unstable"?) sheeting disintegrate into a million tiny pieces after a few years of partial sun, and I felt bad that all of those bits of plastic ended up in the soil and water. I think you're probably right that covering the above-ground plastic under a wooden overhang is the best choice. I'll add it to my design when I get around to building this project. Thanks again for your answers and advice!

zymurgeneticist (author)LynxSys2014-08-05

Thanks LynxSys, good luck and please let us all know how it goes!

zymurgeneticist (author)2014-07-07

Time for another update! We went away for a week and boy did the garden take off in our absence. The valve system is still working great and the whole system is barely using any water.

The first image shows, from left to right, our snow and snap peas, Brussels Sprouts, tomatoes and cucumbers in the background.

The second image is a closer shot of the cucumber vines trained up the trellis with the peas off to the right and the tomatoes to the left. There are a TON of cucumber flowers and many cukes coming in after we pollinated the flowers with a cotton swab.

The third image is our prolific Campari tomato plant, it's already 5 foot tall and climbing up the bamboo stake.

The forth image shows, from back to front, beats barely visible behind the kale, rainbow chard, mizuna, and arugula barely visible in the right corner.

Looks like we'll be busy harvesting soon!

Just goes to show you that you should post replies when tired...

The fourth image shows, from back to front, beets barely visible behind the kale, rainbow chard, mizuna, and arugula barely visible in the right corner.

Chikpeas Brother (author)2014-07-07

Nice build! Did you find nutrients leached from the soil over time? That was a problem with the last raised bed garden I put together.

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Bio: Avid homebrewer, guerrilla geneticist and constant crafter. I am always elbow deep in at least three projects while dreaming up another. Currently I'm exploring ... More »
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