Most people have grown a plant in a pot. Growing vegetables in containers is similar but needs a little more care and attention, particularly at the start. The idea is to reproduce a mini garden ecology. Disregard advice that suggests mono-crops in soilless potting mixes with chemical fertilizers. Think rich moist soil, mulches, companion planting and micro-environments.
Purchase or build sturdy, wide and deep containers. Except when you are growing shallow-rooted vegetable such as lettuce (see below), your vegetables need as much space as possible to expand their root systems. 14” – 24” square containers, 12” deep are optimum but any large pot (2 gallons plus) will do. Modern self-watering containers are excellent for the busy gardener.
Most containers need adequate drainage. However, lettuce and all salad greens can be grown in 4” deep trays with no drainage holes. Cover the bottom 3/4” of the tray with pea gravel. Cut out weed-suppressant fabric to fit over the gravel and fill the rest of the depth with your soil mix.
Make your own premium potting soils, even if that means adding something to bagged mixes. Soil is the essential element of your container garden and should be rich, fertile and porous with a slightly open texture. Coir coconut fiber is a better soil base than sphagnum peat moss: it is renewal, holds water and does not degrade as fast. Avoid potting soils that are mostly ground up bark.
Compost is essential to contain moisture and provide nutrients and a home for microbes. Use your own or a good organic supply. Most commercial mixes have perlite or vermiculite to aid drainage. I prefer sand: it is cheap, natural and provides some minerals. For vegetables, avoid mixes with water retaining polymers (little bits of soft plastic). These are considered inert but may allow residue to enter the plants.
Your container soil also needs minerals. Ordinary garden soil can provide these but should be added in limited quantities – it tends to compact. Use minerals with trace elements if you can find them. Add small amounts of ground rock dust or organic fertilizers.
Lastly, if you want to produce a living soil ecology, you need to enhance the microbial life. Compost, worm castings and rich garden soil all provide microbes. If you add garden soil, be sure to include a few worms.
My own container soil recipe by volume:
- 4 parts of coconut coir, peat moss or recycled soil from past containers
- 2 parts Alaska humus and/or sieved garden compost
- 1 part sand
- 1 part garden soil if I feel like it
- Some natural mineral
- A handful of alfalfa pellets if I have them
Mix everything well in a large container or wheelbarrow. Fill the planting containers to 1/2″ from the top and water until moist—the soil level should go down at least 1”
Sun and Water
Locate you container in a place that gets at least 6 hours of sun a day and is convenient for watering. Heat loving vegetables such as beans, tomatoes, squashes, peppers and eggplants need lots of full hot sun. Cool season vegetables such as salads, spinach, Brassicas, greens and peas like a little shade, especially in the afternoon.
You will have to water containers more often than in a normal garden, often once a day. To cut down on watering, mulch your containers with compost, leaves, grass clippings, paper or porous plastic materials such as weed blocker. If regular watering is a problem, consider an automatic watering system with a timer. You can purchase a number of sophisticated drip systems. Others systems use capillary action or pop bottles with a special conical top that is pushed into the soil.
Most varieties of vegetable can be grown in a container, especially if you are willing to harvest sooner and smaller. Choose varieties that have a shorter growing season and are cultivated for their smaller size.
Determinate tomatoes are bush-like: choose cherry or smaller types (I like Gold Nugget). Many miniature hybrids are bred specially for container growing: carrots (Little Finger, Thumbelina); cabbage (Baby Head, Fast Ball); beets (Little Ball, Burpee Golden). It is best to experiment with different varieties over a number of seasons to find those that grow best.
If you grow from seeds, it is best to start them inside and then plant out into the containers when they are ready. Transplants need to have at least 2 real leaves and be hardened off by putting them outside for a longer time each day over a 10-day period. The benefit of seeds is that you chose the varieties you prefer and know how each plant is grown.
It is much easier to buy plants in pots. These should be hardened off for a couple of days and carefully replanted, making sure their roots are well spread and not pot-bound. Try a good local nursery to find more unusual varieties. Tomatoes and Brassicas (cabbage types) should be planted as deeply as possible to help create more roots. Most other vegetables are planted at the same depth as they grow.
Cover all transplants with floating row covers until they look strong; water well.
I think plants in pots look lonely; I bunch my pots together so their leaves touch and intermingle. I seldom plant only one variety of plant in a pot: tomatoes like basil to keep them company; lettuce goes with cress, arugula, chicory and mizuma.
Most vegetables have plants they love or hate. Check the companion-planting chart (http://www.attra.ncat.org/index.php/complant.html) to find vegetable that go well together.
One reason to put plants together is to create soil shade. Garden soil is always cooler than the air. It is essential that containers do not get too hot as roots and many soil microbes die when they reach 100F.
Even in a small back yard or patio, you can be eating highly nutritious and flavorful vegetables all the way to October.