Brussels Sprouts

Brussels sprouts are a large, slow‐growing, cool‐weather crop. Plant seedlings in July for harvest in fall and winter. The sprouts become sweeter after the first frost. They are hardy to frosts and light freezes. They are an excellent source of vitamins A and C. Brussels sprouts are a member of the brassica family and should be planted in an area that has not grown other brassicas (cabbage, kale, broccoli) for at least one year.

Site Requirements

Brussels sprouts do best in full sun, at least six hours of direct sun. It thrives in rich well drained soil with a pH between 6.0‐7.5. Mix in a shovel full of composted manure, granular all purpose fertilizer, and lime to each planting hole.

Planting

Brussels sprout seedlings can be planted in April and May for summer harvest. Seeds can be started indoors under lights in February and March.

Brussels sprouts for fall harvest need to mature before fall frosts begin. Seeds should be started 100‐115 days before the first frosts. Therefore, by late June seeds should be started in flats indoors under lights or outdoors in the Portland area. Transplant seedlings to the garden when they are four weeks old. Starts can be planted July through mid August. Since Brussels sprouts prefer cooler temperatures, choose an area in the garden that may be partially shaded by larger summer crops.

Brussels sprouts will grow quite large, so space them 18‐24” apart in rows 24‐40” apart. You can interplant your Brussels sprouts with fast growing crops, such as lettuce or cilantro to make productive use of your garden space and to help shade the small sprout seedlings. Cover your new planting with floating row cover to prevent attacks from cabbage loopers and other chewing insects.

Water Requirements

How much water your plants will require depends on the soil and weather. Water new transplants daily, or when the top 2” of the soil is dry. Once they reach 12” Brussels sprouts need average, evenly moist soil. Avoid overhead irrigation, instead use drip or flood irrigation or hand watering.

Fertilizing

Brussels sprouts are heavy feeders, and benefit from a side dressing of composted manure or all purpose granular fertilizer two weeks after transplanting. Repeat side dressing once a month for the next two months.

Tips

You can boost sprout size, but reduce quantity, by removing the top growing point once sprouts have formed on the bottom 12”. This can also be done when the harvest slows to help redirect energy to sprout development. Remove the bottom leaves if they turn yellow.

As a sprout begins to swell, remove the leaf just under it. This will channel energy into the sprout development.

Harvesting and Storage

Brussels sprouts are harvested from the bottom of the stalk up. Continuously pick summer sprouts when they are marble size. If you want to harvest all at once instead of continuously, pinch the top of the stalk off 4‐ 8 weeks before intended harvest date. When harvest time arrives, cut off entire stalk 1” above ground level.

Fall sprouts are harvested when they are 1‐2” across and firm. Use a sharp knife to remove the sprouts and lower leaves. You can also harvest all at once by cutting the entire stalk 1” above ground level. Store entire stalk in root cellar, cool basement, or garage. Brussels spouts will store 3‐5 weeks when kept at 32°F.

Pests and Diseases

Many problems that can occur with Brussels sprouts are due to weather and cultural conditions. Plants will bolt in reaction to hot weather and drought. Correct planting time, moderate and consistent moisture, soil amending, and row covers are all strategies to improve growing conditions.

• Damping‐off occurs in cool, wet weather and prevents seedlings from emerging, or causes seedlings to die off. Replant new seeds in an area with better drainage, or add more compost and wait for warmer weather.
• Cutworms can often mow down all of your seedlings in one night. Spinosad is an organic control for cutworms. Nematodes can help control cutworms also.
• Cabbage loopers and imported cabbage worms leave large irregular holes in leaves coupled with bits of green excrement. They can also burrow holes in sprouts. For prevention cover new seed beds with floating row cover. Spray with Bt to stop infestation.
• Aphid damage often appears as curled, deformed or yellow leaves. You may find colonies of green or grey aphids on the undersides of the leaves and growing tips. Also, sticky sap on leaves and stems and white aphid skeletons are quite prevalent. There are numerous sprays and control measures to help combat aphids.
• Flea beetles chew dozens of tiny holes in the leaves. For prevention cover new seed beds with floating row cover until plants are 8” tall. Dust with diatomaceous earth or spray with pyrethrin.
• Mildews appear as white patches, preceded by reddish patches, on the leaves and stems. Both downy and powdery mildew are fungal issues. Downy mildew can also cause roots to be misshapen with rough, cracked skin. First remove as much of the infected areas as possible. There are numerous fungicides listed for edibles, such as Serenade, that can prevent the spread of powdery mildew.
• Root rot may appear as pale or yellowing leaves and stunted plants. Roots will be dry and black at the center. It is caused by a soil fungus initiated by overwatering and/or very heavy soil. There is no recovery from root rot. Amend soil with at least 2” of compost and allow the area to become slightly dry between waterings to avoid root rot.
• Snails and slugs leave large holes in leaves or eat new transplants when they feed at night. They often leave iridescent trails on leaves and the ground. Slug baits and beer traps are just two ways to control them.
• Club root is a soil fungus that stunts and deforms roots. It may kill seedlings or weaken older plants. Infected plants become stunted and wilt on warm days and leaves may turn slightly yellow. There is no cure for club root, and the fungus will persist in the soil for many years. Remove and destroy infected plants, including the soil ball around the roots. Plant new transplants in a different area of the garden. Do not plant brassica crops in an area that has had club root for at least 7 years.