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How Do I Grow Brussels Sprouts?

source: Joe Gardener

Brussels sprouts are cool-season brassicas that taste even better after they have been kissed by frost. Nothing complements a main course in fall quite like fresh Brussels sprouts that came straight to the kitchen from the garden. They have a delicious, slightly crunchy, nutty flavor and can be served roasted, sautéed, steamed and even raw. If you want to grow Brussels sprouts in your garden, here’s what you need to know.

Brussels sprouts are cruciferous vegetables that, believe it or not, are the exact same species as cabbage, broccoli, kale, collard greens and kohlrabi. With their thick stems that grow 2-3 feet tall and their large buds, Brussels sprouts are one of the most interesting looking plants in an edible garden and really stand out in winter after less-hardy plants have faded.

Where, When and How to Plant Brussels Sprouts

Brussels sprouts take a long time to mature — anywhere from 85 to 145 days, depending on the variety — and they grow best when temperatures stay below 70° degrees. In the North, to ensure plants have adequate time to produce a few harvests, it’s usually best to start seeds indoors or in a cold frame a month to six weeks before your zone’s last frost date. In frost-free regions, Brussels sprouts may be sown from fall to spring.

Be conscious of the length of your growing season and the specific days to maturity of the varieties you are growing. For spring- or summer-sown crops, the goal is to time it so the plants will mature as the weather gets colder. If it’s hot at that time, plants will become bitter and flimsy.

Brussels sprouts seeds are sown just a quarter-inch deep and will germinate in five to eight days. However, whether starting indoors or direct sowing, the seeds will require a soil temperature of between 60° and 85° in order to germinate.

The soil should be neutral to slightly alkaline, between 6.6 and 7.8 pH. A soil test will tell you if the soil is where it needs to be.

Brussels sprouts grow best when the soil temperature stays below 70°. In the warmer months, apply organic mulch such as shredded leaves, arborist’s wood chips or straw to keep the soil from overheating.

Watering Brussels Sprouts

Brussels sprouts require 1-2 inches of water a week, so if rainfall comes up short, make up the difference with supplemental watering. If you have a drip irrigation system, it will serve shallow-rooted Brussels sprouts well.

Putting down 1-2 inches of organic mulch will help retain water while also moderating the soil temperature.

Fertilizing Brussels Sprouts

A pH level that’s very close to neutral is especially important for Brussels sprouts so that the plants take up nutrients efficiently.

For a fall harvest, fertilize by side-dressing every three to four weeks through the end of summer. Never apply more than the fertilizer bag recommends. It is important to not go overboard with nitrogen. Otherwise, plants will have many leaves but paltry sprouts.

When the plants are reaching maturity and starting to produce, it’s time to stop fertilizing, so the plants concentrate on sprout growth rather than leaf growth.

Brussels Sprouts Pests & Diseases

When Brussels sprouts receive even moisture and experience minimal root disturbance, they will perform much better and be less susceptible to pests and disease. Still, there are pests and pathogens to look out for.

Because Brussels sprouts are the same species as cabbage, they attract the same pests: cabbage loopers, cabbage root maggot, cabbage worms (the larvae of either cabbage white butterflies or diamondback moths), slugs, cabbage aphids and flea beetles.

Small moths and butterflies fluttering above your Brussels sprouts may be scouting out a place to lay their eggs, which will become the worms that eat the leaves.

An easy, chemical-free way to stop pests on Brussels sprouts is to cover plants with a lightweight, translucent floating row cover from the day you put transplants in the garden.

You don’t have to keep row cover on the whole season (you can since Brussels sprouts are not dependent on pollinators to mature) but leave it on at least until the plant is well developed and more resilient.

Insecticidal soap is a good contact pest control for the aphids, and Bt is a biological control that’s safe for humans and pets, yet effective against cabbage worms. And as the weather cools off and plants mature, pests should become almost non-existent.

To avoid disease on Brussels sprouts, refrain from overhead watering because wet foliage invites pathogens to take hold. Water at the base of plants instead.

Leaf spot is the most common disease. Fungicidal controls, such as neem oil, help, and I always advise removing any diseased leaves whenever they are found.

If disease becomes an issue, refrain from planting brassicas in that spot for at least two seasons. Giving the area a break from brassicas will reduce the brassica pathogens in the soil.

Harvesting Brussels Sprouts

After a few frosts, Brussels sprouts will be at peak flavor. However, you can pick sprouts whenever they have firmed. It’s also OK to pick sprouts before they have reached that variety’s maximum size. Be sure to harvest from the bottom up.

The leaf below each sprout may be broken off. Then cut off each sprout where the bud meets the stalk.

Some varieties may be topped off about four weeks before the first frost to encourage budding. This can make for more production in a shorter window of time.

If plants are free from disease, leave them in the garden even after all the sprouts have been picked. A plant may surprise you by continuing to produce long after you thought it was done. Even after hard frosts, a plant can remain viable. The season can be extended for quite some time by using a frost blanket when nights dip to 25°.


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