Colorado Master Gardener Program | Yard and Garden Publications | CMG GardenNotes #724

Vegetable Gardening in Containers

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For basic information on container gardening, refer to CSU Extension Fact Sheet #7.238, Container Gardens.

Container vegetable production is somewhat more demanding than growing flowers and other ornamentals in containers. Quality of most vegetables is based on the soil’s ability to provide a constant supply of water and nutrients. Vegetables become strong flavored, stringy, and tough under dry or low fertility conditions. With the limited root spread in a container, the gardener must frequently and regularly supply water and fertilizer. In growing container flowers, minor lapses in daily care may interrupt flower production, but flowering eventually resumes with returned quality care. With container vegetables, minor lapses in daily care may significantly reduce produce quality.

Cool Season Vegetables

Cool season vegetables prefer the cool growing temperatures (60°F to 80°F) of spring and fall. Most are intolerant of summer heat. They do tolerate light frosts. Leafy and root vegetables prefer full sun, but are tolerant of partial shade. They are intolerant of reflected heat during the summer season.

Spring crops are typically planted two to four weeks before the average spring frost date. Along the Colorado Front Range, spring planting times are mid-April to early-May. Most are replanted in mid-July to mid-August for a fall harvest.

The quality of these vegetables is directly related to their ability to grow rapidly in a good soil mix under frequent light fertilization and a constant supply of water. Crops become strong flavored if they become dry.

Table 1. Cool Season Vegetables
Vegetable	Minimum Container Size*	Minimum Direct Sunlight Per day	Remarks
Beets	8” deep	8 hours	Best in cool temperatures, grow a spring and fall crop. To give space for root development, thin greens to three inches”. A consistent supply of water and nutrients promotes the rapid growth essential for quality produce.
Broccoli Cabbage Cauliflower Collards Kale	10” deep 5 gallons per plant	8 hours	Best in fall production (e.g., plant mid July for fall harvest along the Colorado Front Range). Minimum spacing per plant is 18 inches by 18 inches. A consistent supply of water and nutrients promotes rapid growth and is essential for quality produce. Heavy feeder, requiring frequent light fertilization. Crops develop a strong flavor if the soil gets dry.
Carrots	8”-12” deep	8 hours	Best in cool temperatures, grow a spring and fall crop. Use short root varieties, like Short & Sweet or Scarlet Nantes. Roots will crack and be strong flavored if the soil gets dry. Thin early to two to three inches apart. Decorative foliage.
Chard	8” deep	6 hours	Space to six or more inches between plants in a row. Harvest outer leaves allowing plants to continue to grow. Makes an excellent “cut and grow again” crop. Colored varieties are very decorative. Responds to frequent light fertilization. A consistent supply of water and nutrients promotes the rapid growth essential for quality produce.
Kohlrabi	8” deep	8 hours	Best in cool temperatures, grow a spring and fall crop. A consistent supply of water and nutrients promotes the growth essential for quality produce. Never allow soil to become dry. Kohlrabi is a heavy feeder, requiring frequent, light fertilization.
Leaf Lettuce	8” deep	6 hours	Grow as a spring or fall crop; avoid hot summer temperatures. Use softhead or leaf types. As the young crop grows, thin to nine-inch spacing; crowding (competition for space, water and nutrients) reduces quality. A consistent supply of water and nutrients promotes the rapid growth essential for quality produce. Responds to frequent light fertilization. Lettuce become strong flavored if the soil become dry, during hot weather, and with crowded plants.
Onions (green)	6” deep	8 hours	Onions require a consistent supply of water. Never allow soil to become dry. Thin the crop by harvesting young plants. Plant in early spring. A consistent supply of water and nutrients promotes the rapid growth essential for quality produce.
Peas	8” deep	Full sun	Not well suited to container gardening. Best in cool temperatures, grow a spring and fall crop. Use dwarf, edible-pod or snap types for salads and stir-fry. May be grown in hanging baskets or trellised. Needs good air circulation to avoid powdery mildew.
Radish	8” deep	8 hours	Best in cool temperatures, grow a spring and fall crop. A consistent supply of water and nutrients to promote rapid growth is essential for quality produce.
Spinach	8” deep	6 hours	Best in cool temperatures, grow a spring and fall crop. A consistent supply of water and nutrients promotes the rapid growth essential for quality produce.
Turnips	8” deep	8 hours	Best in cool temperatures, grow a spring and fall crop. When large enough to make greens, thin to four inches, allowing roots to develop. A consistent supply of water and nutrients promotes the rapid growth essential for quality produce.
* Larger container sizes will make crop easier to care for, providing a bigger supply of water and nutrients.

Warm Season Vegetables

Warm season vegetables prefer warmer summer temperatures (70°F to 95°F) and are intolerant of frost. They are typically planted after the average spring frost date as summery weather moves into the areas. Along the Colorado Front Range, planting time would be mid-May to early June. Warm season crops need full sun.

Table 2. Warm Season Vegetables
Vegetable	Minimum Container Size*	Minimum Direct Sunlight Per Day	Remarks
Beans	8” deep	full sun	In a long box 12-inch wide, plant bush beans or trellis pole Beans have a high water requirement during blossoming. Beans drop blossoms with dry soil or excessive wind.
Cantaloupes Muskmelons	5+ gallons per plant	full sun	May be trellised to conserve space. Compact varieties preferred for container gardening. With male and female blossoms, may need hand pollination. Needs good air circulation to minimize powdery mildew.
Cucumbers	8” deep 3+ gallons per plant	full sun	Grow bush-types in hanging baskets or on a trellis (vines grow 18-24+ inches long). Grow strong vining-types on trellis. Needs good air circulation to minimize powdery mildew. Young plants are very sensitive to wind burn.
Eggplant	8” deep 4-5 gallons per plant	full sun	One plant per container. Requires night temperatures above 55°F for pollen development.
Peppers	8 deep 2-5 gallons per plant	full sun	One plant per container or space to 14 to 18 inches in row. Requires night temperatures above 55°F for pollen development. Decorative, attractive plant with fruit.
Summer Squash (Zucchini)	8 deep 36 by 36 space	full sun	Compact varieties more suited to container gardening. Great in a whiskey barrel size container. One plant will produce six or more fruit per week. Has male and female blossoms. May need hand pollination. Needs good air circulation to minimize powdery mildew. Keep fruit picked for continued production.
Tomatoes	12” deep 2-5 gallons per plant depending on cultivar (plant size)	full sun	Cultivars vary in mature plant size from determinate bush) types to large, indeterminate vines over 6 feet tall. Patio types (small vines) are great for container gardening and may be grown as hanging baskets or trellised. Standard garden types require a larger container (like a whiskey barrel) and trellising. Requires night temperatures above 55°F for pollen development. Crowding cuts yields and increases disease potential. Blossom end rot (black sunken area on bottom of fruit) is a symptom of inconsistent watering (too wet or too dry) or inadequate pot size.
* Larger container sizes will make crops easier to care for, providing a bigger supply of water and nutrients.

Additional Information

CMG GardensNotes on vegetable gardening

Block Style Layout in Raised Bed Vegetable Gardens, #713
Colorado Frost Dates, #740
Frost Protection and Extending the Growing Season, #722
Growing Vegetable in a Hobby Greenhouse, #723
Irrigating the Vegetable Garden, #714
Mulches for the Vegetable Garden, #715
Sample Planting Guide for Raised-Bed Garden, #721
Sample Vegetable Garden Seed Catalogs, #712
Tomato Early Blight, #718
Tomatoes – Growing Tomatoes, #717
Vegetable Garden Hints, #719
Vegetable Garden: Soil Management and Fertilization, #711
Vegetable Gardening in Containers, #724
Vegetable Planting Guide, #720
Water Conservation in the Vegetable Garden, #716

Authors: David Whiting, with Carol O'Meara and Carl Wilson; Colorado State University Extension.

CMG GardenNotes are available online at www.cmg.colostate.edu
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Copyright. 2010-12. Colorado Master Gardener Program, Colorado State University Extension. All Rights Reserved. CMG GardenNotes may be reproduced without change or additions, for nonprofit educational use.

Revised January 2012