self-irrigating planters (aka SIPs)

Andrew has been doing a ton of research on self-contained self-irrigating planters (SIPs).

Who needs land to grow stuff? Apparently, SIPs are great for balconies and rooftops … I’m thinking you could even put them out in alleys or any type of unused space that gets decent sun, really.

You can buy a self-irrigating planter kit via EarthBox if you have the cash to burn and prefer things to look nice and pretty. But we like finding new uses for old things, which is how we came across – and decided to use – the homemade bucket system.

Essentially, a homemade SIP consists of two buckets or tubs and a lid, one stacked inside the other so there are a few inches of interior space between the two. The top bucket holds the potting mix and plant, while the bottom bucket acts as a water reservoir that you replenish only when it’s gone dry. (Self irrigation. Get it?)

The six basic steps as I recall them:

1. Drill a hole

First you drill a hole (we used a 3-inch hole saw) in the lid of the top bucket, where the plant will poke through.

2. Drill more holes

Drill a 1 1/2-inch hole through the same lid, and another through the bottom of the top bucket. This is where you’ll run a 1 1/2-inch watering pipe or tube down from the top lid to the bottom bucket stacked underneath.

3. Drill yet another hole

Drill another (3-inch or so) hole in the bottom of the top bucket. This is where you’ll place your water-wicking mechanism that will help draw water up from the bottom bucket/water reservoir to the top bucket (more on that in step No. 5).

4. Drill even more holes

Drill several smaller holes throughout the bottom of the top bucket, so that the roots can reach down and hopefully eventually get to the bottom bucket/water reservoir directly. With this step, we’re making what’s called the “perforated soil barrier” in the diagram above.

5. Drill one last hole

Three to four inches up the side of the bottom bucket, drill a small drainage hole. This will let you know when the reservoir has reached its water-holding limit. When water starts to pour out while you’re filling up (via the watering pipe or tube), you know you’re good.

6. Make the water-wicking thingee

Now you need something to wick the water in the bottom bucket up to the top bucket that holds the potting mix and plant. For our “wicker,” we punched a bunch of holes in a plastic cup, filled it with potting mix and placed it in the 3-inch hole at the bottom of the top bucket. (Some folks use a swimming pool filter, which we couldn’t readily find.) The idea is that water will permeate through the cup’s holes and the potting mix will help draw and disperse the moisture to the rest of the bucket.

Done! Now for a much more detailed and visual explanation, check out Josh Mandel’s instructions on how to build a homemade SIP.

Homegrown Evolution, from where I took the above diagram, also has some great links to articles.

Our plan is to do some A/B testing and see if the plants do better in-ground or in buckets. Andrew found someone selling used food-grade five-gallon buckets with lids for a dollar apiece. (Horray for Craigslist.) We bought some non-PVC tubing and a hole saw, and Andrew spent the better part of a Sunday building six SIPs, with various modifications to protect the plants from wind, etc. for the first few days. We used organic potting mix, not soil, since we’ve read that potting soil can contain icky bugs and organisms that might thrive and multiply in a closed environment. We also sprinkled a small handful of Dr. Earth 5-7-3 organic fertilizer around the base of the plant, and covered the lid with black plastic sheeting – cut from garbage bags – to keep the temp inside (hopefully) a tad warmer.