Growing vegetables in containers may be a suitable alternative when outdoor gardening space is not available. In situations where space is not an issue, but the soil is poor, growing in containers and using a good potting mix may be preferable. Adequate sunshine, water, and fertilizer plus a well-drained growing medium are essential for successful container gardens.
Almost any type of container can be used if it provides good drainage through holes in the bottom or around the sides near the bottom. If adding holes, drill four or more 1/4-inch holes evenly spaced around the container bottom. Most vegetables require containers that hold at least 6 to 8 inches of potting mix. Root crops such as carrots require deeper containers. Compact or “space saver” varieties will generally perform well in containers.
Container gardens require a growing medium that drains well, yet does not dry out too fast. “Soilless” potting mixes have several advantages over soil. They are free of plant disease organisms and weed seeds, are less likely to compact, hold moisture and plant nutrients well, and are lightweight—making the container more portable. “Soilless” potting mixes can be purchased from garden centers and retail outlets.
Nearly all vegetables grow and produce best when grown in full sunlight. Plants that bear fruit, such as cucumbers, tomatoes, peppers, and eggplant, require the most sun. Leafy vegetables (lettuce, cabbage, greens, spinach, and parsley) tolerate more shade than root crops (radishes, beets, and onions). Containers should be placed where they will receive at least 6 hours of sunlight per day. Caution, in Washington county where heat is intense during the summer months, place potted vegetables where they will be in the shade during the afternoon.
Plants grown in containers require frequent watering because they dry out quickly from sun and wind. Some plants may require daily watering. Apply enough water to reach the bottom of the container and allow the excess to drain through the drainage holes. Never allow the soil to dry out completely between waterings; this may cause the plants to drop their fruits and flowers. However, over-watering also will slowly kill plants because the roots will not receive enough oxygen. When watering, avoid wetting the leaves, especially if watering late in the day. Wet leaves encourage the development of plant diseases.
Container-grown plants require fertilization more frequently than field-grown vegetables because they have less soil from which to obtain nutrients. A soluble fertilizer (15-30-15 or 20-20-20) applied once every week or two is recommended. This can be applied while watering.
When growing standard-sized tomato varieties, use a stake or cage to keep the vines upright. If staked, plants should be pruned to produce manageable one- or two-stem plants. To prune a tomato, remove the small shoots that form in the axils of the leaves and stems. If these shoots are not pinched out, they will grow and make the plants difficult to train. Tie the stems loosely to the stake. Tomato cages should be made of fencing material of at least 4-inch mesh so the fruit can be harvested easily. Cages should be at least 24 inches in diameter.