Broccoli is a cold-weather vegetable that struggles in intense heat, bolting (prematurely flowering) when temperatures consistently exceed 75°F. Successful cultivation in Massachusetts (USDA Hardiness Zones 5b to 7a) requires careful timing to avoid the hot summer months. Gardeners must utilize two distinct planting windows—one in spring and one in late summer—to ensure a harvest before summer heat and before the hard freeze of winter.
Planting Schedule for Spring Harvest
The goal of spring planting is to mature the broccoli head before the arrival of typical Massachusetts summer heat, usually beginning in mid-to-late June. Start seeds indoors six to eight weeks before the average last expected frost date. Since the last frost date generally falls between late April and mid-May, indoor seeding should occur in late March to early April.
Seedlings must be hardened off before transplanting into the garden. As a frost-tolerant crop, broccoli can be transplanted outdoors two to three weeks before the last frost date, typically in late April or early May. While the plant withstands light frost, protection is necessary if a hard freeze is predicted. This spring crop is less reliable because an early temperature spike can trigger bolting, causing a small, unusable head.
Planting Schedule for Fall Harvest
The fall crop is generally preferred because heads develop as temperatures naturally cool, resulting in larger and sweeter harvests. This planting requires “back-timing,” calculating the seeding date by counting backward from the expected first fall frost. The average first frost date ranges from late September in western regions to mid-October near the coast, with early October being a common target.
To ensure maturity, the seed-to-harvest window for most broccoli varieties is approximately 85 to 100 days. Counting back this duration from the first week of October places the optimal seeding window between late July and early August.
Starting seeds in the heat of August presents a challenge, as high temperatures can inhibit germination and stress young seedlings. It is beneficial to start these seeds indoors or in a shaded, protected nursery area. Providing extra water and temporary shade helps the young plants survive until they can be transplanted into the garden in mid-to-late August.
Preparing the Site and Protecting the Crop
Broccoli thrives best in full sun, receiving at least six to eight hours of direct sunlight daily. The soil should be fertile, well-drained, and rich in organic matter to support rapid growth. Brassicas prefer a soil pH that is slightly acidic to neutral, ideally ranging between 6.0 and 7.0.
A primary concern is pest management, specifically controlling the imported cabbage worm and cabbage looper. These caterpillars quickly skeletonize leaves and bore into the developing head. The most effective preventative measure is the use of floating row covers, which physically block the adult white cabbage moths from laying eggs.
Once pests are present, an application of Bacillus thuringiensis (Bt), a naturally occurring bacterium, is an effective organic control method. Bt is ingested by the caterpillars and disrupts their digestive system without harming beneficial insects or humans.
Harvesting
When the main, central head is firm and fully developed, harvest it by cutting the stem at a slant about six inches below the head. Leaving the plant in place often encourages the growth of smaller, secondary side shoots, extending the harvest season.