Wicking Beds: Water-wise Gardening Part 3
Finally - the culmination of the wicking bed! Thanks for reading through all parts of this series to learn more about water-efficient gardening. I think the extra steps and labor in the beginning are worth it when your watering chores are reduced and your garden is thriving. Last week, I discussed the construction of our bed, as well as the gravel reservoir. Today, I'll cover the last two layers of the wicking bed - let's jump right in.
Once you have your gravel reservoir in, you're going to place a layer of filter fabric down. This will allow water to flow through freely without fine sand or soil running down into your gravel reservoir and clogging your perforated watering pipe. In the picture, you can see the fabric we placed down and hung over the edges, much the same way we did the black plastic lining. Filter fabric is one of my favorite things on this entire earth - no exaggeration. I always hav
Remember, it's important to monitor the depth of each layer of your bed. Our gravel reservoir is 4-6 inches, the wicking layer is about 4 inches, and the soil layer is 10-12 inches. We chose construction sand (sometimes called river sand or concrete sand) as our wicking material due to it's adhesive strength and capillary action. Sand is not an expensive material in itself; however, due to it's weight it can sometimes become expensive if you are having it delivered. Constructing a small bed should be easy enough, but for our purposes, we had a dump truck load brought in. And having extra is always a good thing - sand is one of my favorite materials for gardening and landscaping as it fulfills a variety of purposes. Maybe I'll dedicate a future post to sand-only.
We filled our wicking layer of the bed with 4 inches of sand and tried to make it as level as possible. We used rakes to do this, being very careful not to puncture holes in the plastic. Keeping things level is very important - you don't want some areas of your raised garden flooded while other parts are dry or evaporating more quickly. To check this, we filled our reservoir and waited to see if the sand was wicking up evenly. Water will always tell you where the low spots are!
It took a really long time to fill the gravel reservoir the first time - like, almost thirty minutes. Again, our bed is 4 foot x 20 foot, so that's pretty big and it's going to take awhile the first time. You can see in the last picture above that the sand was not wicking evenly and we had some low spots, so we were then able to even things out and make everything level. I was glad we did this before adding the soil level so that we could make adjustments as needed. It was really cool to see the water coming up from below - working exactly as it should!
Remember the overflow pipe I mentioned in part two of this series? When filling your gravel reservoir, you need to know when you've added enough water. Unlike traditional watering from the top, you're not going to be able to see your soil getting saturated, so that's where the overflow pipe comes in. The overflow pipe is your watering "gauge", so to speak. When watering your bed from the fill pipe, you will know that your wicking layer has been saturated when water runs out of the overflow. The overflow pipe should be right at the top of your wicking layer, and it needs to be protected before moving to the next step.
To protect my overflow pipe, I wrapped a layer of filter fabric around it to prevent soil or sand from getting into the holes and clogging it. Then, I covered it with a layer of river rock to hold everything in place. In the picture above, you can see what it looked like before adding the soil.
This is my favorite part! I mean, I'm a gardener, right? Let's get the dirt going!
Not quite - since I didn't want to contaminate my soil, I stained the outside of my concrete blocks with an acid-reactive stain first before adding the last layer. This added another day to the process but it was worth it to me. This is, of course, a matter of personal preference. Just something to think about before adding your soil.
Adding the soil layer to the wicking bed was the easiest part of the whole process - we simply dumped the soil in using the tractor bucket, checked the depth, and leveled everything out. One note about soil: If you have a heavy clay soil, it will not wick and stay water-logged. It's best to use a mix of sandy loam and compost or a type of soil designed for raised garden beds or container gardens. I've seen some people use peat moss in the mix, as well; however, this is not a renewable resource, so think about whether or not you want to use this. I used a product that is a combination of non-shrinking compost, composted rice hulls, granite sand, and gypsum. This mixture retains moisture well enough without causing drainage problems.
Now the wicking bed is ready to be planted! Remember, you will water from your fill pipe until water comes out of the overflow. Easy enough to stick a hose in there while doing other garden chores. You should have a garden that retains water better, is more resistant to disease, more efficient, and easier to maintain. I hope to post an update this summer showing how my plants are doing in the wicking bed and would love to hear from you, too! Comment below if you're interested in trying this project for yourself!