Collard greens are a dark, leafy vegetable belonging to the Brassica family, making them relatives of cabbage and kale. Unlike many other garden vegetables, this hardy plant performs best and develops its most desirable flavor in cool weather conditions. Collards do not form a tight head, instead growing as an open rosette of large, waxy leaves. The single most important factor for a successful, high-quality harvest is correctly timing the planting relative to seasonal temperature shifts.
Spring Planting Schedules
Gardeners aiming for an early summer harvest must plant collards to mature before the arrival of intense summer heat. The primary marker for spring planting is the average date of the last expected frost in your region. Sow seeds directly into the garden two to four weeks before this final frost date to allow the plant to establish itself.
For a quicker start, transplants can be set out approximately three to four weeks before the last spring frost is anticipated. Collard greens are cold-hardy, capable of surviving light frosts and temperatures that dip into the upper teens Fahrenheit. This early start is necessary because the plants require a lengthy cool period to grow large, tender leaves.
The risk of planting too late is that the plants will “bolt,” or prematurely send up a flower stalk, triggered by consistently high summer temperatures, often above 80°F. Bolting causes the leaves to become bitter and tough, ending the harvest. Therefore, timing the spring planting to ensure maturity before the summer heat arrives is paramount for a palatable crop.
Fall and Winter Harvest Timing
The period leading up to the first light frosts of autumn is considered the optimal window for growing collard greens. This timing allows the plants to mature in gradually cooling temperatures, which dramatically improves the leaf flavor. Calculating the planting date involves counting backward from the average date of your region’s first expected autumn frost.
For direct seeding outdoors, collard seeds should be sown eight to ten weeks before that first frost date to allow for germination and full development. Using transplants shortens this window, allowing them to be set out six to eight weeks before the frost is anticipated.
The resulting cool-weather growth cycle is superior because cold temperatures activate a natural mechanism within the collard plant. This converts starches stored in the leaves into sugars, a process known as “sweetening” that occurs after a light frost (typically below 32°F). The leaves become noticeably sweeter and more tender after this exposure. In the Southern United States and other mild climates (USDA hardiness zones 8 and above), fall-planted collards can often be harvested throughout the entire winter season.
Seed Starting vs. Transplants
The method chosen for starting collard plants directly impacts the calendar timing needed for a successful harvest. Starting with established transplants offers a significant advantage by immediately giving the plant a head start. This approach is particularly helpful for spring planting, ensuring the collards have sufficient time to mature before the summer heat causes bolting.
If you choose to start seeds indoors for a spring crop, add a lead time of four to six weeks to account for the necessary indoor growth period. For example, if transplants go out three weeks before the last frost, indoor seeds must be planted seven to nine weeks before that same date. Conversely, direct sowing seeds outdoors is possible when the soil can be worked, typically two to four weeks before the last frost.
For the preferred fall harvest, transplants are often used to ensure the plants are large enough to withstand the first frost and grow vigorously through the cooler months. Starting seeds indoors for the fall crop is an option, but the timing must be precisely calculated to avoid seedlings struggling with mid-summer heat. Using transplants helps bypass the challenge of germinating seeds in hot soil conditions.