Wicking Beds: Water-wise Gardening Part 2
In my last post, I discussed the Wicking Bed's history, benefits and why I chose to try it in the hot, dry climate of the Texas Hill Country. If you haven't read my post on how wicking beds originated, I suggest you check it out. There are some steps to follow when building your own wicking bed, so if you're interested in a more efficient watering system, read on for how I did it!
Construction of The Bed
People make raised beds out of all kinds of materials these days - a simple Google Image search for "Raised Garden Beds" reveals a host of materials from wood to metal to stone to random objects. Depending on what you are growing, you have your choice of materials that range in price and life-expectancy. We decided to go with solid concrete block for ours. These blocks come in a 4x8x16 dimension and we chose them for several reasons:
1) Stability: I knew I would be sitting on the edge quite a bit and wanted it to be stable. These blocks weigh about 30 lbs apiece and are stable when dry-stacked without the use of mortar.
2) Strength: Concrete will last forever and I won't have to redo the beds five years down the road. I have used wood in the past, and even lined with black poly plastic, it was still only a few years before they were rotting.
3) Versatility: If needed, this could be taken apart easily and redone if there was a leak, etc., unlike working with mortar.
4) Cost: While natural stone would have looked nice, it definitely ain't cheap. Concrete is more cost-effective and readily available. It can also be stained or painted to improve the look.
We started by laying a footing of pipe bedding (you can use gravel or anything stable). We were working on a slope so we had to build it up more on one side to get it level. As we laid the first course, my husband constantly checked each block to make sure it was level - this is very important. Thankfully, he has a background in construction and a field level since there was quite a slope. This helps. You cannot "do it by eyeball", as I usually do.
Once the first course is laid, you can build up the sides, staggering the blocks for stability. It took about two pallets of block (around 216 blocks) to construct a bed that was about 4x20 and a little less than two feet high. My back was killing me by the end of the day, but other than being heavy, the blocks really are easy to work with in terms of getting everything straight and level
Your bed needs to be tall enough for at least 4-6 inches of gravel for your reservoir, 4 inches for the wicking layer (this is very important - no more than four inches or it will not wick), and 10-12 inches of soil. This ends up being a little less than two feet high.
You will want to notch out one block for the use of your overflow pipe (see pictures for top and side views). I placed mine on the short end of my bed where the watering pipe will go. This is how you will know when you have watered enough. DO NOT FORGET THIS STEP. The overflow pipe should be placed at the top of the wicking layer (for our bed, this was about ten inches above ground). We used a short piece of 3/4 inch PVC pipe with holes drilled in it. We attached an elbow for the outside end of the pipe so that water would drip down. It should stick out of your bed a few inches - I'll show you how it works later.
Creating the Reservoir
Once the bed is built, you are going to create the gravel reservoir. This is where water will be stored for your garden bed, much like the water table underground. We used pipe bedding for our reservoir, but you could use any type of gravel. The first step is to line your entire bed with plastic. We used 6 mil. black poly plastic lining and we doubled it to prevent any leaks. Be extremely careful with your plastic lining around the sharp edges of rocks, etc., so it does not tear. We cleared the bottom of the bed of any rocks and raked it smooth to make sure the plastic would not rub against anything that would cause it to tear. Your entire bed should be lined, draping over the edges, as pictured. We used STEGO tape to tape the black plastic around the overflow pipe.
Once you have the plastic lining in place, a very small layer of gravel should go in (1 inch or less), and then your perforated pipe. We bought pipe that is used for French drains, so it already had perforations in it; however, you can also use PVC pipe and drill holes in it. This pipe should be about the length of your bed and should be placed in the middle so that water flows through on all sides. The watering pipe should be connected at one end (the same end as your overflow pipe) and stand up taller than the height of your bed. This is where you will do your watering.
Then, you should add the remainder of your gravel (4-6 inches, remember?). This is where a tractor comes in handy if you're building a large bed. This is your reservoir layer where the water for your bed will be stored.
In my next post, I'll show you how we built the last two layers and finished construction of the wicking bed. Comment any questions you have below!