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Brussels Sprouts 'Long Island Improved' · Zones 2–9
Growing Details
Zone-by-Zone Planting Calendar
| Zone | Indoor Start | Transplant | Direct Sow | Harvest |
|---|---|---|---|---|
| Zone 3 | May – June | June – July | May – June | September – October |
| Zone 4 | May – June | June – July | May – June | September – November |
| Zone 5 | May – July | June – July | May – June | September – November |
| Zone 6 | May – July | June – August | May – July | September – December |
| Zone 7 | May – July | June – August | May – July | September – December |
| Zone 8 | June – August | July – September | June – August | October – January |
| Zone 9 | July – August | August – September | July – August | October – February |
Complete Growing Guide
Start your Long Island Improved seeds indoors 12-14 weeks before your first expected fall frost for the best results. This timing ensures your plants develop strong root systems before hot summer weather and allows sprouts to mature during the cool fall months when they develop their signature sweetness. Sow seeds ¼ inch deep in seed starting mix and maintain soil temperature around 60-65°F for optimal germination.
Prepare your garden bed by working in 2-3 inches of well-aged compost or rotted manure to create the rich, fertile soil these heavy feeders require. Choose a location with 6-8 hours of direct sunlight and ensure good drainage – waterlogged soil leads to root rot and stunted growth. Test your soil pH and aim for 6.0-6.8; if your soil is too acidic, work in lime several weeks before transplanting.
Transplant seedlings when they're 4-6 inches tall and have developed their second set of true leaves. Space plants 18-24 inches apart in rows 3 feet apart – cramped plants produce smaller, less flavorful sprouts. Water transplants deeply immediately after planting and mulch around the base to retain moisture and suppress weeds.
Fertilize with a balanced 10-10-10 fertilizer at transplanting, then side-dress with nitrogen-rich fertilizer (like fish emulsion) every 3-4 weeks during active growth. Stop nitrogen feeding 6 weeks before your expected harvest to prevent overly loose sprouts. These tall plants benefit from staking or hilling soil around the base as they mature – mature plants can reach 3 feet tall and become top-heavy.
Avoid the common mistake of harvesting too early. Long Island Improved truly shines after experiencing at least two light frosts, which converts starches to sugars and eliminates any bitterness. Remove yellowing lower leaves regularly to direct energy into sprout development, and be patient – this variety's extended growing season is what creates its exceptional flavor profile.
Harvesting
Begin harvesting Long Island Improved sprouts from the bottom of the stalk upward once they reach 1-1.5 inches in diameter and feel firm when gently squeezed. The sprouts should be tight, compact, and bright green – avoid any that have begun to yellow or feel loose. The ideal harvest window is after your first two frosts but before hard freezes below 20°F.
Twist and snap sprouts off with a sharp downward motion, or use a sharp knife to cut them cleanly from the stalk. Harvest in the morning when sprouts are crisp and turgid from overnight moisture. Start with the largest, lowest sprouts first – this encourages continued development of smaller sprouts higher up the stalk. Leave about ¼ inch of stem attached to each sprout to prevent the outer leaves from falling off.
You can continue harvesting for 4-6 weeks from a single plant, working your way up the stalk as sprouts mature. The top growing tip can also be harvested and eaten like small cabbage once you've finished with the sprouts.
Storage & Preservation
Fresh Long Island Improved sprouts store best in the refrigerator crisper drawer, unwashed and loosely wrapped in perforated plastic bags. They'll maintain peak quality for 2-3 weeks when stored at 32-35°F with high humidity. Don't wash until ready to use, as excess moisture accelerates decay.
For longer storage, blanch whole sprouts in boiling water for 3-4 minutes depending on size, then immediately plunge into ice water. Once cooled and drained, freeze in airtight containers for up to 12 months. The post-frost sweetness of this variety makes frozen sprouts far superior to most store-bought options.
Fermenting is another excellent preservation method – quarter the sprouts and ferment like sauerkraut for 3-4 weeks. The natural sugars developed after frost create particularly flavorful fermented sprouts. You can also dehydrate halved sprouts at 125°F for 8-12 hours to create crispy chips that retain much of their nutty flavor.
History & Origin
Long Island Improved Brussels sprouts emerged in the late 1800s from the fertile market gardens of Long Island, New York, where immigrant Dutch and German farmers adapted European Brussels sprouts varieties to American growing conditions. The variety was specifically selected for its ability to withstand the harsh northeastern winters and produce consistently large harvests for the growing New York City market.
This heirloom represents generations of careful seed saving by Long Island truck farmers who selected plants that produced the most uniform, flavorful sprouts while maintaining cold hardiness. The 'Improved' designation reflects decades of selection for larger sprout size, better stalk strength, and enhanced cold tolerance compared to the original European varieties.
By the early 1900s, Long Island Improved had become the standard commercial variety for northeastern growers and remained dominant until hybrid varieties were introduced in the 1960s. Today, it's cherished by home gardeners and small-scale farmers who prize its reliable performance and exceptional flavor development after frost – qualities that made Long Island a Brussels sprouts powerhouse for nearly a century.
Advantages
- +Develops exceptional nutty sweetness after frost exposure that eliminates bitterness
- +Produces abundant harvests with 40-60 sprouts per plant when properly grown
- +Extremely cold hardy, surviving temperatures down to 10°F with protection
- +Strong, sturdy stalks rarely require staking even when fully loaded with sprouts
- +Extended harvest period allows picking for 4-6 weeks from a single plant
- +Superior storage life compared to hybrid varieties - maintains quality for 2-3 weeks refrigerated
- +Excellent disease tolerance including good resistance to clubroot and black rot
Considerations
- -Long growing season of 100-120 days requires early planning and consistent care
- -Plants are heavy nitrogen feeders requiring regular fertilization throughout the season
- -Susceptible to cabbage worm damage during late summer growth period
- -Lower sprouts may become oversized and loose if not harvested promptly
- -Requires 2-3 square feet per plant making it space-intensive for small gardens
Companion Plants
Plant Together
Nasturtiums
Acts as trap crop for aphids and flea beetles, repels cucumber beetles
Thyme
Repels cabbage worms and whiteflies, attracts beneficial insects
Dill
Attracts beneficial wasps that parasitize cabbage worms
Onions
Repels cabbage root flies, aphids, and other brassica pests
Marigolds
Deters nematodes and general garden pests, attracts beneficial insects
Carrots
Loosens soil around Brussels sprouts roots, doesn't compete for nutrients
Celery
Natural pest deterrent that repels cabbage worms and aphids
Beets
Different root depth prevents competition, may improve soil structure
Keep Apart
Tomatoes
Both are heavy feeders competing for nutrients, tomatoes may stunt brassica growth
Strawberries
Inhibits Brussels sprouts growth and development through root competition
Mustard
Same family (Brassicaceae) attracts identical pests and diseases, depletes soil nutrients
Pests & Disease Resistance
Resistance
Good tolerance to clubroot and black rot
Common Pests
Cabbage worms, aphids, flea beetles, cabbage loopers
Diseases
Clubroot, black rot, downy mildew, powdery mildew