When To Plant Brussel Sprouts In Wisconsin

If you’re planning your Wisconsin garden, knowing when to plant brussel sprouts is key to a great harvest. This cool-season crop thrives in our climate, but timing is everything to avoid summer heat and fall frosts.

Getting the schedule right means you’ll get those sweet, tender sprouts after a frost. Let’s break down the ideal timeline and methods for success in Wisconsin.

For most of Wisconsin, the best strategy is to start brussel sprouts indoors. You should sow your seeds about 4-6 weeks before your last expected spring frost date. Since Wisconsin’s frost dates vary, this is your first thing to check.

For southern Wisconsin (Zone 5), aim to start seeds indoors in early to mid-April. In northern zones (4 and colder), target late April to early May. This gives the plants a strong head start before they go outside.

Understanding Your Wisconsin Frost Dates

Your local average last frost date is your gardening anchor. Here’s a general guide:

Southern WI (Zone 5): Last frost around May 1-15.
Central/Northern WI (Zone 4): Last frost around May 15-30.
Far Northern WI (Zone 3): Last frost can be as late as early June.

Always verify with your county extension service for the most accurate date. Planting too early risks a surprise frost, while planting to late exposes young plants to summer heat they dislike.

Transplanting Seedlings Outdoors

Your seedlings are ready for the garden when they have 4-6 sturdy leaves and are about 5-6 inches tall. The most important step is hardening them off. This means gradually introducing them to outdoor conditions over 7-10 days.

Start by placing them in a shaded, sheltered spot for a few hours.
Gradually increase their time outside and exposure to sun and breeze.
By the end, they should be able to handle full outdoor conditions day and night.

Transplant them into your garden 1-2 weeks after your last frost date. In southern Wisconsin, this is typically mid to late May. For northern areas, aim for early June. The soil should be workable and warmed up a bit.

Can You Direct Sow in Wisconsin?

Direct sowing seeds right in the garden is possible but tricky. It requires a long, cool growing season. In Wisconsin, if you choose to direct sow, you must do it as soon as the soil can be worked in very early spring, around the time of your last frost date.

This method is less reliable because the young seedlings grow slower and are more vulnerable to pests and weather swings. Starting indoors is generally recommended for a guaranteed harvest.

Choosing the Right Varieties for Wisconsin

Selecting a variety with a maturity date that fits our shorter growing season is crucial. Look for varieties that mature in 90-110 days from transplanting.

Long Island Improved: A reliable, classic heirloom that handles cold well.
Churchill: An early maturing hybrid (about 90 days) that’s perfect for our climate.
Diablo: Known for its disease resistance and high yield.
Jade Cross: A compact, hybrid variety good for smaller spaces.

These types are proven performers and can handle Wisconsin’s fall temperature dips.

Site Selection and Soil Preparation

Brussel sprouts need full sun—at least 6 hours of direct sunlight daily. They are heavy feeders, so soil prep is vital.

Choose a site that hasn’t grown other cabbage family crops (like broccoli or kale) recently to prevent disease.
Work in 3-4 inches of compost or well-rotted manure into the soil.
Mix in a balanced, slow-release organic fertilizer according to package directions.
Ensure the soil is well-draining but moisture-retentive. They like consistent moisture.

Spacing and Planting Care

Give your plants plenty of room to grow. Crowding leads to smaller sprouts and increases disease risk.

Space transplants 18-24 inches apart in rows that are 30 inches apart.
Plant them at the same depth they were in their pots.
Water them in thoroughly with a starter fertilizer to reduce transplant shock.

Consider using floating row covers right after planting. This protects them from early pests like cabbage worms and gives them a gentle warmth boost.

Seasonal Care Through Summer and Fall

Brussel sprouts require consistent care. They need about 1-1.5 inches of water per week. Mulching heavily with straw or shredded leaves helps retain soil moisture, keeps roots cool, and suppresses weeds.

Side-dress the plants with a nitrogen-rich fertilizer when they are about a foot tall to support all that leafy growth. Keep a close eye out for cabbage worms and aphids, handpicking or using an organic control like Bt if needed.

The Importance of Cool Weather

Brussel sprouts flavor actually improves after a light frost. The cold triggers the plant to convert starches into sugars, making the sprouts taste sweeter. Don’t rush to harvest them at the first sign of cool weather.

In fact, your main harvest will likley come in mid to late fall. This is when Wisconsin gardens shine for this crop.

Harvesting Your Wisconsin Brussel Sprouts

Harvest begins from the bottom of the stalk upward. Pick sprouts when they are firm, about 1-1.5 inches in diameter, and still tightly closed.

Twist or snap off the lower sprouts first as they mature.
Remove the yellowing leaves at the base of the plant to encourage further growth.
You can also top the plant (cut off the very top growing point) about 3-4 weeks before you want the harvest to end. This tells the plant to put all its energy into maturing the remaining sprouts.

Before a hard freeze (usually below 20°F), you can harvest the entire stalk. Cut it at the base and hang it in a cool, dark place like a garage or basement for several weeks of storage.

Common Problems and Solutions

Even with good care, you might encounter issues. Here’s a quick guide:

Loose, poorly formed sprouts: Often caused by to much heat during development or inconsistent watering.
Small sprouts: Usually from overcrowding, poor soil nutrition, or lack of water.
Cabbage worms: The white butterflies are laying eggs. Check undersides of leaves and use row covers or Bt.
Aphids: A strong spray of water from the hose can dislodge them, or use insecticidal soap.

FAQ: Growing Brussel Sprouts in Wisconsin

What is the latest I can plant brussel sprouts in Wisconsin?

For a fall harvest, you can plant a second crop by direct seeding or transplanting in very late June to early July. Choose a fast-maturing variety and be prepared to water frequently during summer heat.

Can brussel sprouts survive a Wisconsin winter?

The plants themselves are biennials but are usually killed by our harsh winters. However, the sprouts on a harvested stalk store well in cold conditions. You cannot typically overwinter the plant in the ground for a second-year harvest here.

Why are my plants tall but not producing sprouts?

This is often due to planting to early in hot weather or nitrogen imbalance. To much nitrogen promotes leafy growth at the expense of sprout formation. Ensure they get that crucial period of cool weather in the fall.

Should I remove the lower leaves?

Yes, as you harvest sprouts from the bottom, remove the yellowing leaf below that sprout. This improves air circulation and directs energy. But leave the healthy upper leaves intact, as they are the engine for the plant.

Following this Wisconsin-specific schedule gives your brussel sprouts the best chance. With proper timing and care, you’ll be rewarded with a bountiful harvest of sweet, homegrown sprouts well into the autumn season.