One of the recent crazes in vegetable container gardening is the Earthbox™, a rectangular self-watering container that grows great tomatoes, peppers, cucumbers and beans (and other vegetables, I’m sure). It is an ideal solution for small space vegetable gardening, such as on a balcony or patio.
There are a lot of different types of self-watering containers on the market now, and you can even make your own, but I like the rectangular shape of these guys. They are just the right size for two cherry tomato plants, and I have also grown five hot pepper plants in one, which was fun, because I planted five different varieties.
I love mine, and can share with you some do’s and dont's that I’ve learned from experience...
The Earthbox™ consists of several parts: a main rectangular box, a perforated “false bottom” that creates a water reservoir in the very bottom, and a fill tube. The older ones like mine also have an interlocking support grid on the bottom of the main container which supports the false bottom. The newer ones have this built in.
The fill tube in the corner allows you to fill the bottom chamber, below the grid, with water. When you run water into this fill tube from a garden hose, the water fills the chamber below the soil level. When it is filled up to the correct level, the extra water starts to run out a little hole in the side, so it is impossible to overfill the chamber in the bottom.
One challenge with vegetable container gardening is how fast most containers tend to dry out. This is the brilliance of the Earthbox™ - it solves this challenge.
Tito and I enjoy camping in the summer a lot, and it can be a challenge to find a neighbor to come over to water while we’re away for a few days. With the Earthbox - no problem! (Of course, in my case, I have a bunch of other stuff that does need watering, so my neighbor Karen comes over, bless her.)
Self-watering containers of any kind do not work by suspending the plant roots in the water! They work by wicking water up via capillary action through the potting mix to where the plant roots are.
I just watched a You Tube about self-watering containers, made by the company trying to sell you their brand - and they said “water your newly planted self-watering container for a day or two when first planted, until the roots of the plant can grow down into the water”. This is ridiculous - plant roots don’t grow down a foot in two days. But you do need to water from above when you first plant it, because dry potting mix will not wick water. It’s like “priming the pump”, you need to get the potting mix moist before the wicking action will occur.
But the most serious problem that can occur in self-watering containers (any self-watering container) is the build up of salts from fertilizer and naturally-occurring dissolved minerals in water. In an ordinary pot that drains at the bottom, this is less of a problem, because the excess fertilizer salts are flushed out by watering deeply from the top and draining out the bottom. When you have a good 24 hour rainstorm, this happens automatically.
But with any container that is wicking water up from down below, the water and fertilizer is drawn up from the water chamber, and then evaporates from the top, over and over and over again, which over time will concentrate the fertilizer salts and dissolved minerals that are naturally dissolved in the water, into the potting mix.
Earthboxes now come with a fertilizer strip, that is supposed to work in a time-release fashion to minimize this problem. But over time, especially over multiple seasons if you use the same potting mix, any evaporative system is going to build up minerals and salts.
The solution is to either:
I get around this issue another way. I don’t use any chemical fertilizer at all. I use a high proportion of homemade compost in my potting mix, which is qualitatively very different, and to this I add a proportional ratio of complete organic fertilizer, which is a combination of minerals. (Here is the link for complete organic fertilizer). COF is slower to release than the chemical fertilizers or the strips that come with the Earthbox, and their uptake by plants is mediated by the organisms in the fresh, living compost.
I have many, many large container gardens, both self-watering and not, and every fall I dump the potting mix out of all of them into 3 large “Brute” trash cans. I pull out the plants and their bigger roots, break up the potting mix, and store it over the winter in these covered trash cans.
In the spring, I lay out a large tarp in the middle of the lawn, and mix up new potting soil by combining 2 parts “old” potting mix with 1 part homemade compost. The compost is fully decomposed, so its microbes are alive and its nutrition is available to the plant roots. I also mix in a portion of Complete Organic Fertilizer.
But in any container, because you are basically using "sterile" potting mix without the presence of normal soil microorganisms, you are sort of stuck with using artificial fertilizers if you have no rich compost. Organic fertilizers are slow-release because they rely on soil microorganisms and myccorhizal fungi for help getting into the plant.
The Earthbox is a really wonderful option for vegetable container gardening or gardening in small spaces like balconies or patios, and even though I don’t need one (with my big in-ground garden), I love the cherry tomatoes and habanero peppers that I grow in mine every year. I hope you enjoy yours as well. Just swap out or refresh the potting mix in the spring.