Container Cultivation

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The critical differences have to do with size: How much soil can it hold (and how deep is the soil?), and how much water? Big plants need big pots (I like about 40 quarts of soil for artichokes or summer squash). Soil 8 inches deep satisfies most plants, and 5 or 6 inches is enough for salad greens, but carrots need 12 inches. Reservoirs need to be big enough to allow at least three or four days between waterings. I like at least 1 quart of water for every 8 quarts of soil, but more is better. Self-watering containers are available from the suppliers listed below, and you also can make your own — see “DIY Self-watering Container,” below.

Self-watering containers greatly simplify things. If there is water in the reservoir, there’s enough water in the soil, period. Simply refill the reservoir before it’s empty — unless rain is in the forecast. If excess water flows out the overflow hole(s), it will take valuable nutrients with it.

Selecting Soils

Soil in either a traditional or a self-watering container provides plants with water and food. In a traditional container, the soil needs to receive and hold as much water as possible. In a self-watering container the soil needs to be able to absorb water from the reservoir and disperse it evenly throughout the container. Both tasks are best accomplished by a soil containing peat moss and some perlite and/or vermiculite. Peat has a unique ability to absorb and hold moisture. (Yes, there are questions about the sustainability of this slowly renewable resource, but we think limited use of peat for container and seed-starting mixes is OK. — Mother)

I like to recreate as nearly as I can the conditions that work best in my regular garden, so I use soil that contains about 50 percent compost. I’ve had excellent results using a 50-50 mix of good compost and sphagnum peat-based potting soil. If you have any doubts about the compost quality, add about a cup of balanced organic fertilizer per 40 quarts of soil mix. I make my own fertilizer blend: one-third cup each of green sand, rock phosphate or bone meal and a nitrogen source such as alfalfa or soybean meal. I add a tablespoon of Azomite — a rock dust that provides micronutrients and trace minerals.

Note: When peat-based soil dries out, it does not re-absorb water well, and it does not properly wick water. A dry traditional container must be watered, then watered again in a few minutes, until the soil is evenly moist. A dry self-watering container needs water on the soil surface until even moisture is restored. Then fill the reservoir.

Best of luck with your new versatile, low-maintenance container garden!

DIY Self-watering Container

You can make your own self-watering container from a couple of 5-gallon plastic buckets. (From our food co-op, I’ve scored free buckets that had housed peanut butter and other such things.)

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