Brussels sprouts are a cool-weather vegetable that thrives when maturation aligns with the dropping temperatures of autumn and winter. The plant requires vegetative growth followed by a cool finish to develop firm, sweet sprouts. Located in USDA Hardiness Zone 7, your garden experiences average minimum winter temperatures between 0°F and 10°F. This climate allows the plant to fully develop its tall stalk and numerous buds before the first hard freezes arrive, supporting a successful, extended Brussels sprout season.
Understanding Climate Requirements
The timing of planting is governed by the plant’s sensitivity to temperature. Brussels sprouts develop best when the average air temperature is consistently between 50°F and 70°F, supporting steady growth. Temperatures above 80°F during sprout development are detrimental to the harvest. Excessive heat causes the plant to produce higher concentrations of glucosinolates, the compounds responsible for bitterness. Prolonged heat can also cause the sprouts to “bolt,” or open up, resulting in a loose, poor-quality product.
Planting should ensure the harvest occurs after the first light frosts of the season. A temperature drop into the upper 20s or low 30s Fahrenheit is not damaging to the mature, cold-hardy plant. This gentle chilling is beneficial, as the plant converts starches stored in the sprouts into sugars. This natural mechanism enhances the flavor, mellowing bitterness and yielding a sweeter vegetable. Brussels sprouts can tolerate temperatures down to around 20°F, making the Zone 7 winter an extended harvest window.
Specific Planting Schedules for Zone 7
Successful cultivation in Zone 7 relies on staggering planting to align the 90- to 110-day maturation period with the onset of cool weather. The most reliable schedule is for a fall and winter harvest, utilizing the typical first frost date around November 15. For this main crop, transplant seedlings into the garden between late July and mid-August. This requires starting seeds indoors six to eight weeks earlier, meaning sowing should begin in late May or early June. The plants spend the summer establishing root systems and tall stalks, with sprouts forming as temperatures cool in the fall.
The harvest window for the fall-planted crop usually begins in late October or early November and can continue through February. Sprouts should be harvested from the bottom of the stalk upward once they are firm and one to two inches in diameter. Attempting a spring-planted crop in Zone 7 is challenging due to the rapid transition into summer heat. For a spring crop, start seeds indoors in late January or early February for a garden transplant in early to mid-March, shortly after the typical last frost date of April 15. The spring crop must be harvested quickly by late May, before consistent 80°F days cause the sprouts to become bitter and loose.
Starting Plants: Seeds vs. Transplants
Starting from seed or using pre-grown transplants impacts the timeline and cost of the crop. Starting with transplants is the most common method, as it shaves six to eight weeks off the time the plant spends in the garden. Established seedlings typically have four to six true leaves and a robust root system, allowing them to establish faster. This speed is advantageous, especially for the challenging spring crop where time is limited before summer heat.
Starting Brussels sprouts from seed offers the benefits of lower cost and access to a wider variety of cultivars. For indoor seed starting, sow seeds half an inch deep in a sterile mix, ensuring bright light for strong, non-leggy growth. Seedlings must be “hardened off” before moving outdoors. Hardening off is the process of gradually acclimating young plants to outdoor conditions. Over seven to ten days, expose the seedlings to increasing durations of direct sunlight and wind, preparing them for the garden and minimizing transplant shock.