Wicking Bed Experiment
So I used our neighbor’s old kiddie pool to try a proof of concept this summer. A Wicking bed is simply an enclosed reservoir of water over which you put a growing medium and grow stuff. It is supposed to be low water use and the research I found was intriguing enough to want to try it!
So, figuring the easiest and cheapest way to try this was with the old pool, I raked up some of the horrible gravel in our backyard and put 3 inches worth of it into the bottom after I put down landscape fabric to minimize scratching and damage to the pool. I’ve read that ideally you would have 12 inches of water reservoir and another 12 of media, but the pool isn’t that deep, so 3 inches is it. The nice thing about this pool is that it's essentially double walled so it provides a little insulation around the edges from the heat.
I filled the pool with water so it would be easier to level the gravel and determine where the drainage hole should be drilled on the side. The hole is positioned at the top of the gravel.
The theory is that even if it rained or I overfilled the reservoir, the excess water could be drained away and not flood the bed as the water could seep out. Once I was satisfied with the levels, I put down landscape fabric over the gravel and loaded the top with potting soil suitable to container gardening. This was May 15th, then I was too busy to do any more with it and didn’t plant anything in it for over a week, but that gave it enough time to fully soak up the water and hydrate the soil.
So I visited Baker Nursery and got some small potted plants and planted them in the pool garden and in less than one month it looks like this...
I have filled the reservoir with water twice since I put this together, that's a little more than every other week! I've been amazed with the results and am keeping an interested eye on this project as the temperatures heat up and see how long between waterings it can go through the summer.
--------------- UPDATE July 25th 2012 ------------------------------------
Well, I can't say enough great things about this experiment. I'm very happy with the results! I've been watering on average every 5 days, so a little more than once a week in the worst of summer. The plants have exploded in growth all over the place. Here's a recent photo as of this morning:
You can see part of the chicken coop and run in the background. The wire fencing around the bed has effectively kept out the dogs and I haven't had a chicken try to jump in now that there is wall to wall greens in the bed. Apparently the visibly open dirt was the siren's call for Easter Chicken to hop the fence.
Everything has grown well and this morning I picked a watermelon out of the garden. I've been picking a few tomatoes and peppers from the bed and of course sweet potato greens. The tomato needed to be tied upright after going a little too long between waterings and when everything wilted a bit there were too many fruits on it for it to perk back up to straight without some help (that's the string). You can see the hose as it is filling up the reservoir, I usually just let it run for about 10 minutes while doing other chores outside. All in all, I'm going to do this again, bigger, deeper and probably more than just one!!
SIDE NOTE: I do have a question for all you out there. I picked my watermelon after observing that the little curled tendril opposite was fully dry and crispy and the melon gave a wonderfully promising sound when thunked. I had tied it up in burlap to keep it out of the dog's reach since it grew outside the fence. Because of this was no soil spot to check for color change. When I cut it up this morning it was pink, not red, and the black seeds were not yet black, but light brown and only changing to black in spots. It still tastes good, but I can imagine how out of this world it would have been if I waited. So what are your secrets for melon picking?
--------------- UPDATE March 20, 2015 ------------------------------------
I've talked with many people about wicking beds since I first posted this article and thought it was time to update this with some of the things I've learned. First, overall I remain impressed with the water conservation properties of a wicking bed! We are moving to a new home a few blocks away and plan to build proper new wicking beds because of the success of this limited experimental garden. This particular experiment taught me a few things:
1. I really only needed to water this garden every 5 days in the worst of the summer. Hard to believe, but in the last couple years I've neglected this garden and it still chugged away pumping out plants. Water conservation is way up there on my favorite things about the wicking bed.
2. This is still a garden that needs regular inputs and attention! The soil needs to be regularly amended and built up just like regular old garden soil. It is more like container gardening than raised bed gardening - at least with the minimal soil profile in this kiddie pool. Compost and slow released fertilizers keep production up, skimping on these items slows down production.
3. Salts will build up in the bed over time. You need to have a plan to deal with this. I think there are a few good strategies for tackling this issue. Just like in a regular garden bed here in the desert, it's a good idea to periodically flood the bed and wash out the salts. Preferably with rainwater if available!!! I’m planning to build my new beds with the bed drain at the bottom and an external pipe on it, that stand pipe can be removed or turned to completely drain the bed down to the very bottom occasionally. This will be even more important if I use my flood irrigation water to supplemental water the beds, as the flood waters are high in salts and have a high pH. Adding rainwater and possibly Aquaponics water will be a critical component in having a healthy bed.
4. 12 inches total is not enough space for both reservoir and soil for many plants to be happy, and some plants won’t ever be happy in a wicking bed. I think of my dead rosemary plant in particular… There are some plants that will thrive elsewhere in the gardens but not in the wicking bed system. Conversely there are some plants that went happy nuts in this system and I have high hopes that they will be even happier in an optimally designed bed (Dill, I’m talkin to you).
5. Plant perennial plants with caution, they might really take over. Sugar cane… need I say more. Ok, I’ll say more – the sugar cane went on a rampage in this bed and pushed over my watering tower in the race to grow ever outward. It has been super happy and I think it’s part of the reason I started to ignore the bed. The sugar cane was just so big and the leaves so serrated that I kinda backed off from going near it as it became difficult to get the hose to the pipe to fill it up. So consider the full size of the cute little baby plants and perhaps save the wicking beds for easier to manage ones!
Let me know if you have any thoughts about wicking beds, or if you have tried your own wicking bed experiments. OH, and I have sugar cane cuttings if anyone wants some - just drop me a personal message and I'll give you exact directions where to pick them up (near 12th St and Glendale Ave in Phoenix).