Cabbage is a cool-season vegetable, a member of the Brassica oleracea family, grown as an annual crop for its dense, leafy head. Consistently mild temperatures are a biological necessity for successful head formation. Temperature is the single most important factor determining whether a plant produces a crisp, solid head or bolts prematurely. This dependency dictates planting timing and necessitates protective measures against climatic extremes.
The Ideal Temperature Range for Growth
Cabbage’s most productive growth occurs within a narrow, temperate band of air temperatures. The optimum range for head development is between 59 and 68 degrees Fahrenheit (15 to 20 degrees Celsius). Growth ceases when temperatures consistently climb above 77 degrees Fahrenheit (25 degrees Celsius), which is why summer planting is avoided in warmer climates.
High temperatures, especially those above 80 degrees Fahrenheit, can trigger bolting, where the plant prematurely sends up a flower stalk instead of forming a tight head. The resulting heads are often loose, bitter, and of poor quality. Conversely, prolonged exposure to temperatures below 50 degrees Fahrenheit (10 degrees Celsius) for several weeks, particularly after the plant has passed its juvenile stage, can also induce bolting. Cabbage plants are resilient to cold, with hardened, mature plants able to tolerate brief dips as low as 15 to 20 degrees Fahrenheit.
Translating Temperature into Planting Schedules
This temperature dependency defines two primary windows for planting cabbage in most regions: a spring crop and a fall crop. For a spring harvest, seeds are started indoors six to eight weeks before the last expected spring frost. Seedlings are hardened off and transplanted outdoors two to three weeks before that final frost date, allowing them to establish roots in the cool spring soil. The goal is for the heads to mature before the intense heat of mid-summer arrives.
The fall crop is often considered superior, as the heads develop during the naturally cooling temperatures of late summer and autumn. Seeds or transplants are placed in the ground in mid-to-late summer, about 10 to 12 weeks before the first expected fall frost. The progressively cooler nights during maturation enhance the cabbage’s flavor, often resulting in sweeter heads. Fall crops may take longer to mature due to the decreasing day length, which slows the rate of growth.
Protecting Cabbage from Weather Stress
Successfully growing cabbage requires mitigating the effects of unexpected temperature swings. Sudden heat waves threaten developing heads, necessitating measures to reduce the ambient temperature around the plants. Applying organic mulch, such as straw or shredded leaves, helps keep the soil surface cool and maintains consistent moisture levels.
To directly shield plants from intense sun exposure, gardeners can use a shade cloth suspended above the crop, which reduces air temperatures and prevents sun scald. Unexpected late spring frosts or early fall freezes can be managed using floating row covers. These lightweight, fabric barriers trap a small layer of insulating air around the plants, protecting young seedlings or newly forming heads from damaging cold temperatures. Consistent moisture is also important, as a well-watered plant can better regulate its internal temperature through evaporation, especially during periods of heat stress.