Windowsill Hydroponics

After seeing a hydroponics presentation by Chip of the Phoenix Permaculture Guild, we thought it might be fun to grow some things hydroponically in our bay window.  The basic design is to have a tray with medium for the plants, and a bucket connected by a tube to collect the nutrient solution. We had a plastic tray with inside dimensions of 18x25x6 inches that we had used for gardening. In the photo on the right you can see plants at about 4 weeks of age. In the foreground are some basil, then rows of arugula and leaf lettuce.
Photo of 4 week old basil, arugula, and letttuce
For the growing medium, we chose gravel. There is a landscaping supply business about 4 miles from here and we drove there and filled a bunch of buckets. The total bill was $4 and the tray holds about a third of what we bought. As you can see on the right, the stones are roughly a quarter inch in their largest dimension and an eighth of an inch at their narrowest. This medium has worked great for our purposes.When growing things hydroponically, you need to sterilize the medium before starting and between crops. We first sterilized it using hydrogen peroxide, but that seemed expensive (about $15 per liter of the strong stuff) since we used more than half the liter. Subsequently we sterilized the gravel by boiling it in our solar oven, but that was pretty tedious. The next time I might try some beer sterilizing chemicals from my homebrew supplies.

Over time we have washed the sand out of the gravel so the medium drains much more quickly now than it did originally.

Photo of gravel with a dime on top for reference as to its size.
The plant roots need to be covered with the nutrient solution but not sit in it continuously. The photo on the right shows where a hole was cut in the tray to attach hardware and a tube to drain the solution out. Originally we tried the non-electric method of feeding the plants. I would raise the solution bucket above the tray so the nutrients would drain into the tray. After 15 minutes, the bucket was lowered and the solution drained out. This was done 5 or 6 times a day. (I was working at home and the setup is by my computer.)Why is there a clamp on drain tube? When I went on vacation I installed a pump to periodically put the nutrient solution in the tray. That worked okay originally when there was sand in the gravel, but after we cleaned most of the sand from the gravel, the water would drain as fast as the pump could work — and the solution level didn’t get very high in the tray. By clamping the tube a bit, the solution drains slower than the pumps fills, so the solution level gets up to the plant roots.
Photo of drain hose coming out of hydroponic tray. The plastic hose is partially clamped to slow the water drainage.
This is the solution capture bucket. Originally an insert from a kitchen garbage can, it holds 2.5 gallons which is roughly what the tray needs to get the solution to the top of the gravel. In this picture, a pump is in the bucket and one can see the white tube that goes to the tray, as well as the black electrical cord to the submersible pump. At the bottom of the bucket is the tube connected to the tray output. The bucket is curved at that point so getting a water-tight seal required using some acrylic caulk along with the hardware. (Brown caulk is what we had on hand.)
Photo of bucket that holds the drained liquid nutrients.
On the right is the submersible pump (not submersed so it could be photographed). I got it at Lowe’s for $20.Farther right is what runs the pump – a timer set for 5 waterings a day. With the pump, the plants seem to grown better. I attribute this to their getting watered in the middle of the night, which I couldn’t do in the non-electric scheme.

The box in back of the timer is a Kill-a-Watt meter – a device my son-in-law got us to measure electric use. I was curious how much electricity the timer and pump use. For two weeks of use, it was .63 KWH.

Photo of submersible pump with attached hose that will deliver nutrient solution to top of gravel.
Photo of timer which causes the pump to water 5 times per day. Attached to timer is electric monitor to see how much electricity is being used.
This is a basil plant grown hydroponically. Note that the roots are very small. Because the nutrients are delivered to them, they don’t have to grow and search them out.
Photo of a basil plant uprooted from the gravel.

Final Comments.

We have lots of sun in Arizona but my experiments with outdoor hydroponics have not succeeded yet.

One disadvantage of the windowsill method is the plants closest to the window do well and the ones back in the shade get a little leggy.

For the nutrient solution, we use Botanicare’s CNS17 formula. It is about $19 per gallon. We use half a cup every 10-14 days when growing, so it lasts quite awhile. The first week when the seeds are sprouting, we use just water, and start adding nutrients the second week.