Purple sprouting broccoli forms clusters of small heads on a stalk that typically exceeds a height of 2 feet. A member of the cole family (Brassica olereacea), it represents a departure not only from the typical green colour of the broccoli we buy in supermarkets, but the growth habit as well. Purple sprouting broccoli is an overwintering vegetable that requires 200 days from planting to harvest. Although more familiar to UK gardeners, this sprouting broccoli can be grown in the United States in areas with a temperate climate.
Select a planting site that receives full sun and has good drainage. Provide a spot that will allow the plants to remain in place throughout the winter without being disturbed.
Loosen the soil to a depth of 6 to 7 inches with a spade or potato fork, and work in compost or composted manure. If the drainage is questionable, rake the loosened soil into a mound to create a raised bed. Use the back of the rake to create a smooth, flat planting bed.
Rake off the top 1/4 inch of soil just before sowing the seeds. Plant them in April or May to a depth of 1/8 inch, with 3 to 4 inches between seeds. Firm the soil over the seeds and keep them uniformly moist until sprouts appear, which should take six to seven days.
Thin the seedlings to 12 to 18 inches apart after they have developed their first set of true leaves. Side dress with manure, compost, fish meal, bone meal or a nitrogen-based fertiliser such as ammonium nitrate. Spread the fertiliser 4 to 6 inches away from the base of the plants.
Apply a 2- to 4-inch deep layer of organic mulch, such as compost, hay or grass clippings. Water weekly to a depth of 6 inches, but do not allow the soil to become saturated. Watch for wilting at midday, which may indicate the need for more frequent watering.
Spray the broccoli plants with Bacillus thuringiensis to control any cabbage worms, cabbage looper and other caterpillars that appear. Control aphids by spraying with pyrethrum. Treat with a fungicide at the first sign of downy mildew, which shows as yellow patches on the leaves and downy growth on lower surfaces of the plants.
Allow the broccoli plants to overwinter. The following March or April, purple sprouts will appear. Harvest sprouts when they reach 1 to 2 inches in diameter, using garden shears to cut just below the sprout to encourage the formation of new shoots.
Cole crops grow best in soil with a pH of 6.0 to 6.8. Plunge the sprouts into cool water immediately after harvest, and store in the refrigerator for up to five days.
Do not plant purple sprouting broccoli where cole crops have grown the previous year, as fungal and bacterial diseases can persist in the soil and infect susceptible plants.