Containers have a limited capacity for storing essential nutrients and moisture that ensure plant growth. The gardener must closely monitor container crops to be sure they are growing uninterrupted which, in turn, leads to the best yield and flavor.
Almost all growing crops demand even moisture—that means never letting the soil go completely dry and never overwatering leaving the potting mix soggy. A compost-rich potting mix may supply nearly all the nutrients a crop will need over the length of a season—but feeding with an organic fertilizer may be necessary where containers are small or multiple plants are growing (nutrients are essential).
Use a moisture meter to monitor watering if you have any doubts about how wet or dry your containers are. All garden centers and nurseries will have both dry and liquid organic fertilizers. Ask which fertilizer they recommend and then follow the label directions carefully; it’s always safer to under fertilize than over fertilize.
Container Vegetable Care and Feeding:
Here are care and feeding suggestion for vegetable growing in containers on a patio, balcony, or roof top.
- Asparagus: Water every five to seven days during the summer and feed twice a year (early spring and late summer) with a complete liquid fertilizer diluted to half strength. When the leaves begin to brown in autumn cut stems to soil level.
- Beets: Keep soil just moist throughout the growing season (never over water). Thin seedlings when they are 6 inches tall to stand 3 to 4 inches apart. After thinning, feed once with a complete liquid fertilizer diluted to half strength. Don’t let the soil crust–gently cultivate with a trowel or hand cultivator.
- Beans: Keep the soil just moist as plants develop. Later water deeply. Once plants are a foot tall (30 cm) high, thin to strongest plants and feed keepers with a complete liquid fertilizer diluted to half strength. Feed a second time when pods begin to form.
- Broccoli: Keep soil evenly moist. Feed with a complete fertilizer at full strength twice during the growing season—first when plants are about 8 inches tall and again before heads begin to form. Broccoli is a heat sensitive and will bolt and flower when temperatures get into the high 70°Fs (21°C).
- Brussels sprouts: Keep the soil evenly moist water; don’t let it dry out. Feed when sprouts are beginning to form with a complete liquid fertilizer at half strength. As the sprouts begin to cluster, twist off the leaves beneath to transfer growing energy to forming more sprouts.
- Cabbage: Keep the soil evenly moist; it must not dry out. Once transplants are established, feed every three weeks until heads begin to form; use high nitrogen, high potassium fertilizer diluted to half strength. Keep soil mounded around the base of the plant to encourage new root development; this will stabilize the plant and hasten maturity.
- Carrots: Keep soil just moist until harvest. Thin seedlings as they grow to 2 inches between the strongest plants. Feed after the final thinning with a complete liquid fertilizer diluted to half strength; feed again two to three weeks before harvest.
- Cauliflower: Keep the soil evenly moist. The most common problem encountered when growing cauliflower is its failutre to set heads. This can be caused by uneven watering or the soil going dry during a heat wave. Feed plants when well-established with a complete fertilizer diluted to half strength and again as curds form. When a head forms, tie the outer leaves up over the head with twine. This will protect the head from the sun and help the curd to blanch.
- Celery: Celery is a bog plant that requires ample, consistent water to thrive. Feed with complete fertilizer diluted to half strength every two weeks. Keep soil mounded up around the base of each plant to stabilize upright growth. Blanch celery quickly by covering the stalks (leaving the top leaves exposed) with a paper bag or opaque plastic seven to ten days before harvest.
- Collards: Keep the soil evenly moist. Mist leaves on hot, dry days. Feed with high nitrogen, high potassium fertilizer at full strength twice during the growing season.
- Corn: Corn requires eight hours of sun each day are to produce the best crop. If full sun is an issue, look for a hybrid suited to your region. Thin plants to 12 inches (30 cm) apart as they mature. Keep the soil evenly moist; don’t let it dry out especially when the weather is hot and dry. Feed with a 5-10-10 fertilizer at full strength every three weeks.
- Cucumbers: Keep the soil evenly moist. Keep the potting mix warm; use black plastic mulch until the weather heats up then switch to aluminum foil; this reflects heat but and light under the foliage which discourages aphids. Feed with a high phosphorus fertilizer diluted to half strength when plant begins to flower and then every other week until harvest.
- Eggplant: Keep the soil evenly moist throughout the growing season; do not let the soil dry out. Feed monthly with a complete fertilizer diluted to half strength. Keep plants in a warm, sunny location. Protect plants on cool nights by covering with light plant blanket; cool weather stunts growth and reduces yield.
- Garlic: Keep the soil just moist—not wet. As plants mature make sure containers are in a warm, sunny location.
- Horseradish: Keep soil mix evenly moist. Feed once during the season with a complete fertilizer at full strength.
- Jicama: Keep the plant in a sunny location for at least six hours each day. Keep the soil evenly moist–never soggy. Feed with a 10-10-10 liquid fertilizer at full strength once during the growing season.
- Kale: Keep the soil just moist. Thin plant to 8 inches (20 cm) apart. Feed with high nitrogen, high potassium fertilizer at full strength twice during the growing season.
- Leeks: Keep the soil evenly moist–never soggy, which can cause rot. Cool weather will not hurt plants. Blanch leeks by setting a section of 2-inch-diameter opaque plastic tubing or pipe over each one when the stems begin to thicken (mounding with soil is not practical in containers).
- Lettuce: Keep the soil evenly moist but not wet until heads form—too much water can cause rot or heading varieties to crack. Feed lightly every two weeks with a complete liquid fertilizer diluted to half strength. Hot weather can cause non-bolt resistant varieties to flower. Protect plants from hot sun with shade cloth.
- Melons: Keep the soil evenly moist; do not let it dry out but be careful not to overwater; overwatering can cause fruit to crack and may reduce sugar content. Keep foliage dry to avoid fungal diseases. Add slow-release 10-10-10 fertilizer into the soil after vines flower; side dress with water soluble fertilizer a couple of weeks before first harvest. Melons thrive in warm temperatures. If weather cools or in short season regions keep soil mix warm by covering with black plastic and positioning containers in direct sun all day. Allow vines to trail or train vines to a trellis if the container is heavy and will not tip. Support trellised melons with netting.
- Okra: Okra grows best in warm weather; sow seed after nighttime temperatures average 65°F (18°C). Keep the soil just moist—never wet.
- Onions: Keep the soil evenly moist throughout growing season to ensure good bulb development—but don’t overwater which can cause rot. Onions are heavy feeders and should be given a 5-10-10 liquid fertilizer at full strength twice a month.
- Peas: Keep soil barely moist. Thin seedlings to 3 inches apart and train climbing types on string netting or wooden trellises when tendrils appear. Feed twice during the growing season with a low nitrogen 5-10-10 liquid fertilizer diluted to half strength (too much nitrogen will stimulate leafy growth at the expense of the pods).
- Peppers: Keep the soil evenly moist but not wet throughout the season and particularly during fruit development. Feed with a complete fertilizer diluted to half strength when plants are well established and once more just before blossoms open. Peppers grow best when night temperatures do not dip below 68°F (20°C) at night and stay between 75-80°F (24-26°C) during the day. Use a floating row cover or shade cloth to protect fruit from sunscald if the weather turns hot (over 90°F/ 32°C).
- Potatoes: Grow potatoes in a sunny location. Keep the soil evenly moist; drought and drench cycles create deformed tubers.
- Pumpkins: Keep the soil evenly moist and do not let it dry out for best fruit development. Avoid wetting leaves which can lead to fungal diseases. Feed after blooming with a 10-10-10 fertilizer at full strength.
- Radishes: Keep the soil evenly; do not let it dry out—but don’t let it get soggy. Thin to strongest seedlings, 3 inches apart. Feed with a 10-10-10 liquid fertilizer, diluted to half strength. One feeding per crop is all that is needed.
- Rutabaga: Keep soil evenly moist throughout the growing season. Thin established seedlings 6 to 8 inches (15-20 cm) apart. Feed one week after thinning and again three weeks after thinning—with a complete liquid fertilizer diluted to half strength.
- Spinach: Keep soil evenly moist throughout the growing season. Once plants are well-established begin feeding with a high nitrogen fertilizer diluted to half strength every two weeks. When plants are 3 to 4 inches (7-10 cm) tall, thin so that remaining seedlings are 6 inches (15 cm) apart.
- Squash: Keep potting mix evenly moist; keep water off foliage which is susceptible to mildew. Grow squash in a bright sunny place for best yield. Place black plastic sheeting around base of plants early in season to conserve moisture and warm plants; later use aluminum foil to conserve moisture and repel insects with bright reflected light under leaves. Feed with a 10-10-10 fertilizer after fruit sets.
- Sweet Potatoes: Once transplants are established, keep the potting mix just moist—never wet. A month after setting in slips, sprinkle a 10-10-10 slow release fertilizer into the soil avoiding contact with the stems.
- Swiss Chard: Keep the soil evenly moist throughout the growing season; too little water will cause the leaves to be stiff and coarse. Thin seedlings when 2 to 3 inches (5-7 cm) tall to 6 inches (15 cm) apart. Feed with a complete liquid fertilizer every two weeks once plants are established.
- Tomatillo: Be sure plants get full day of direct sun. Keep the potting mix just moist throughout the growing season.
- Tomatoes: Keep the soil just moist throughout the growing season; do not let it go dry out and do not overwater (a dry-wet cycle can cause cracking or blossom-end rot). Feed with low nitrogen, high phosphorus food once a month while fruits are developing. Just before harvest stop feeding. Plants sheltered from the wind should get a gentle shake during flowering (this will help ensure pollen drop from anther onto stigma—the tomato has a complete flower that self-pollinates).
- Turnips: Keep soil evenly moist throughout the growing season. Thin established seedlings 6 to 8 inches (15-20 cm) apart. Feed one week after thinning and again three weeks after thinning—with a complete liquid fertilizer diluted to half strength