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Self Watering Planters
I recently got a copy of Ed Smith≠s revised and improved book on growing vegetables in self-watering planters, The Vegetable Gardener’s Container Bible (Storey Publishing, 2011), and decided that making one of his containers might be a good thing for a bored gardener to do before the gardening season begins.
Ed Smith has boiled down years of experience into simple language that anyone can understand. He recommends using self-watering containers instead of traditional pots because they do a better job of keeping the soil evenly moist- a key to success, particularly with veggies.
His book explains that plants are mostly water, so they need water to stay healthy. They need it for photosynthesis (to manufacture carbohydrates) and to carry soil nutrients throughout the plant. Ed explains that plants do best in biologically active soils, those that are “teeming with mostly microscopic creatures that supply plants with food, creatures that help them to assimilate food, creatures that help protect plants from predation and disease.” And those critters need moisture.
Self watering containers
Water is also needed to cool plants in the heat of summer by the process of transpiration – which is the plant equivalent of sweating. In the process of losing water, “transpirational pull” is created – a force that sucks up water from the ground, bringing along soluble nutrients. Ed’s book explains that “Transpiration is the plant’s substitute for a heart; it is the way a plant moves fluids within itself.” A mature tomato plant in mid-summer can use a gallon of water a day.
Self watering containers have water reservoirs so that plants don≠t dry out quickly – sometimes holding 4 gallons or more. And the bottom line is this: when the soil is too dry, all biological activity stops – both in your plants, and in the microorganisms that nurture and nourish your plants.
The Vegetable Gardener’s Container Bible explains that a light, fluffy soil is essential for growing veggies well in pots. Plant roots and soil organisms need oxygen to thrive, so a fluffy soil does better than a compacted one. Ed’s recipe for success is to make a 50-50 mix of potting soil or peat moss with good quality compost.
The potting mix I bought was a bit heavy with sand, so I modified that recipe a bit: I mixed 12 quarts of potting mix and 12 quarts of compost with 2 quarts of perlite, a heat-expanded mineral that looks like bits of white Styrofoam. Perlite holds water on its surface and keeps the mix fluffy but adds no nutrients.
Ed’s book suggests that you can offer a well balanced diet of plant nutrients by adding blood meal, rock phosphate and green sand to the mix. Unlike chemical fertilizers, these nutrients are taken up slowly by plants, so your plants get a nice even supply. He suggests a third of a cup of each for each 40-quart batch of planting mix. Me? I add a cup of Pro-Gro, an organic fertilizer that has all those ingredients, and a quarter of a cup of limestone.
Big self-watering containers can be expensive. A good quality 40-quart container with a 4-gallon reservoir that will be adequate for a big tomato or 4 peppers will cost you about $40. But you can make your own container if you prefer, and I’ve done so for a fraction of that cost. Here is what I did, using Ed≠s good descriptions and photos.
I bought an 18-gallon plastic storage bin that came with a lid, and a 10-foot section of 4-inch vinyl downspout (enough for 4 bins). I made marks on the inside of the container at the top of the water reservoir, 5 inches from the bottom of the bin, and measured the width and length. I wanted to cut the lid to fit inside the bin at the top of the reservoir, so I transferred the measurements onto the lid and drew lines to guide me. I used tin snips to cut the lid, which, admittedly, is a bit of hard work (a jigsaw might work better).
At the lumber yard where I bought the downspout I asked a fellow to cut some 5-inch pieces for me with the “chop saw” used to cut lumber. He accommodated my strange request and I ended up with perfectly cut pieces (I could have used a hack saw to do the job at home).My planter needed 6 pieces of 5-inch downspout (spacers) to adequately support the lid – now the base of the soil compartment – sitting inside the bin.
To wick the water up into the soil compartment, I cut 2 holes in the lid (each hole a little smaller than the downspout I used as spacers). I attached two spacers right below the holes and later filled them with potting mix. To attach the spacers to the lid, I drilled small holes in the lid and the spacers, and wired them in place. That prevents them from moving. The wicking spacers are perforated – each has a dozen three-eighths-inch diameter holes drilled in it. Lastly I cut a fill-hole in the side of the bin at the top of the water reservoir.
The Vegetable Gardener’s Container Bible is full of good information on growing specific vegetables √ including unlikely candidates for containers like sweet corn and artichokes. I may grow an artichoke or some hot peppers in containers this summer, and then see if I can overwinter them indoors as both are perennial in warm climates. And in the meantime, I≠m making more containers. Give it a try!