Collard greens in Wisconsin need to be planted in early spring for a summer harvest or late summer for a fall crop. Knowing the best time to plant collard greens in wisconsin is key to getting a steady supply of these nutrient-packed leaves. Wisconsin’s short growing season and cold winters mean you have to plan carefully to avoid frost damage or bolting.
Collards are actually quite hardy and can handle light frosts, which even sweetens their flavor. But planting too early or too late can ruin your crop. This guide walks you through the exact timing, step by step, so you can grow collards successfully in the Badger State.
Best Time To Plant Collard Greens In Wisconsin
The ideal window for planting collard greens in Wisconsin depends on whether you want a spring or fall harvest. For spring, aim to sow seeds or set out transplants about 2 to 4 weeks before the last expected frost date. For fall, plant about 6 to 8 weeks before the first expected frost.
Most of Wisconsin falls in USDA hardiness zones 4b to 5b. The last spring frost typically occurs between late April and mid-May, depending on your location. The first fall frost usually arrives between late September and mid-October.
Here’s a quick breakdown for different regions:
- Southern Wisconsin (Madison, Milwaukee, Kenosha): Spring planting: mid-April to early May. Fall planting: late July to early August.
- Central Wisconsin (Wausau, Stevens Point, Green Bay): Spring planting: late April to mid-May. Fall planting: mid-July to early August.
- Northern Wisconsin (Eau Claire, Superior, Rhinelander): Spring planting: early to mid-May. Fall planting: early to mid-July.
Understanding Wisconsin’s Climate For Collards
Wisconsin has a continental climate with cold winters and warm summers. Collards prefer cool weather and grow best when temperatures are between 60°F and 70°F. They can tolerate light frosts down to about 25°F, but prolonged freezing will kill them.
One big challenge is the heat of July and August. If collards are planted too late in spring, they will bolt (go to seed) quickly in the summer heat. That’s why early spring planting is critical for a summer harvest.
For fall crops, you want the plants to mature during the cooler days of September and October. The flavor actually improves after a light frost, so don’t worry if temperatures dip a bit.
Spring Planting: Exact Timing And Steps
For a summer harvest, you need to get collards in the ground as soon as the soil can be worked in spring. The soil should be at least 40°F for seeds to germinate, though 50°F is better.
Here’s a step-by-step plan for spring planting:
- Check your last frost date. For most of Wisconsin, that’s around May 1 to May 15. Look up your specific zip code online.
- Count backward 2 to 4 weeks. That gives you a planting window from early April to late April for southern areas, and mid-April to early May for northern areas.
- Prepare the soil. Collards need rich, well-draining soil with a pH between 6.0 and 7.5. Mix in compost or aged manure a week before planting.
- Sow seeds ¼ to ½ inch deep. Space seeds about 3 inches apart in rows 18 to 24 inches apart. Thin seedlings to 12 to 18 inches apart once they have two true leaves.
- Water consistently. Keep the soil moist but not soggy. Collards need about 1 to 1.5 inches of water per week.
- Use row covers if frost threatens. If a late frost is forecast, cover young plants with fabric or plastic overnight.
If you prefer transplants, set them out at the same time as you would sow seeds. Transplants give you a head start of about 4 to 6 weeks.
Fall Planting: Timing For A Sweet Harvest
Fall-planted collards are often sweeter because the cooler temperatures convert starches to sugars. The key is to plant early enough so the plants mature before the first hard freeze.
Follow these steps for a successful fall crop:
- Find your first fall frost date. In Wisconsin, this ranges from late September (north) to mid-October (south).
- Count backward 6 to 8 weeks. For southern Wisconsin, that means planting in early to mid-August. For northern areas, plant in mid-July to early August.
- Direct sow seeds in the garden. Fall planting works best with seeds because transplants may struggle in the heat of late summer.
- Provide shade if needed. If temperatures are above 85°F when you plant, use shade cloth or plant in a spot that gets afternoon shade.
- Water deeply. Fall crops need consistent moisture, especially during dry August weather. Mulch around plants to retain moisture and keep roots cool.
- Harvest after frost. Wait until after a light frost to pick the leaves for the best flavor. You can continue harvesting until a hard freeze (below 25°F) kills the plants.
Varieties That Perform Best In Wisconsin
Not all collard varieties are created equal for Wisconsin’s climate. Some are more cold-tolerant or bolt-resistant than others. Here are top picks:
- Georgia Southern: A classic, heat-tolerant variety that does well in both spring and fall. It’s slow to bolt.
- Vates: A compact, cold-hardy variety perfect for fall planting. It can survive light frosts easily.
- Champion: Known for its tender leaves and resistance to bolting. Good for spring planting.
- Flash: A fast-maturing variety (about 55 days) that works well for fall crops when time is short.
- Morris Heading: A loose-heading type that’s very cold-tolerant. Ideal for northern Wisconsin.
Soil Preparation And Fertilization
Collards are heavy feeders, so good soil preparation makes a big difference. Start by testing your soil pH. Wisconsin soils tend to be acidic, so you may need to add lime to raise the pH to 6.5 to 7.0.
Here’s how to prepare your soil:
- Clear the area of weeds and debris.
- Loosen the soil to a depth of 8 to 10 inches.
- Mix in 2 to 4 inches of compost or well-rotted manure.
- Add a balanced fertilizer like 10-10-10 at a rate of 1 to 2 pounds per 100 square feet.
- Rake the soil smooth before planting.
During the growing season, side-dress with nitrogen fertilizer when the plants are about 6 inches tall and again when they reach 12 inches. Use blood meal, fish emulsion, or a synthetic nitrogen source.
Watering And Mulching Tips
Collards need consistent moisture to grow tender leaves. Inconsistent watering can make leaves tough and bitter. Aim for about 1 inch of water per week, more during hot, dry spells.
Mulching is a game-changer in Wisconsin. Apply a 2- to 3-inch layer of straw, shredded leaves, or grass clippings around the plants. This helps:
- Keep soil cool in summer
- Retain moisture
- Suppress weeds
- Protect roots from temperature fluctuations
Drip irrigation or soaker hoses work best to deliver water directly to the roots without wetting the leaves, which can cause disease.
Pest And Disease Management
Collards in Wisconsin face a few common pests. The most troublsome are cabbage worms, aphids, and flea beetles. Here’s how to handle them:
- Cabbage worms: Use floating row covers to prevent butterflies from laying eggs. Handpick worms if you see them. Spray with Bt (Bacillus thuringiensis) if infestations are heavy.
- Aphids: Blast them off with a strong stream of water. Introduce ladybugs or lacewings. Use insecticidal soap as a last resort.
- Flea beetles: These tiny jumping beetles leave small holes in leaves. Use row covers, especially on young plants. Diatomaceous earth can help.
Diseases like clubroot and black rot can occur, especially in wet conditions. Prevent them by rotating crops (don’t plant collards in the same spot for 3 to 4 years), ensuring good drainage, and avoiding overhead watering.
Harvesting Collard Greens At The Right Time
You can start harvesting collard leaves when they are about 8 to 10 inches long, usually 60 to 80 days after planting. Pick the outer leaves first, leaving the inner ones to continue growing. This method gives you a continuous harvest for weeks.
For spring-planted collards, harvest before temperatures consistently hit 80°F to avoid bitterness. For fall-planted collards, wait until after a light frost for the sweetest flavor. You can keep harvesting until a hard freeze kills the plants.
Store harvested leaves in the refrigerator in a plastic bag with a damp paper towel. They’ll last about 5 to 7 days. You can also blanch and freeze collards for winter use.
Extending The Season With Cold Frames Or Row Covers
Wisconsin gardeners can push the season further with a few simple tools. Cold frames and row covers let you plant earlier in spring and harvest later in fall.
For spring planting, set up a cold frame 2 to 3 weeks before your last frost date. This warms the soil and protects seedlings from late frosts. You can also use floating row covers directly over the plants.
For fall, use row covers to protect collards from early frosts. They can add 2 to 4 weeks to your harvest window. Just remove the covers during the day if temperatures rise above 70°F to prevent overheating.
Some Wisconsin gardeners even overwinter collards in a cold frame or unheated greenhouse. The plants go dormant in winter and produce new leaves in early spring.
Common Mistakes To Avoid
Even experienced gardeners make mistakes with collards. Here are the most common ones to watch out for:
- Planting too late in spring: This leads to bolting in summer heat. Stick to early April to early May.
- Planting too early in fall: If you plant in late August, the plants may not mature before the first hard freeze. Aim for mid-July to early August.
- Overcrowding: Thin seedlings to 12 to 18 inches apart. Crowded plants produce smaller leaves and are more prone to disease.
- Neglecting soil fertility: Collards need lots of nitrogen. Side-dress with fertilizer every 3 to 4 weeks.
- Ignoring pests: Check leaves regularly for eggs and larvae. Early intervention is key.
- Harvesting too late: Leaves become tough and bitter if left too long. Pick them when they are young and tender.
Succession Planting For Continuous Harvest
To get a steady supply of collards all season, use succession planting. This means planting small batches every 2 to 3 weeks. Here’s a sample schedule for southern Wisconsin:
- First planting: April 15 (spring crop)
- Second planting: May 1 (spring crop)
- Third planting: July 15 (fall crop)
- Fourth planting: August 1 (fall crop)
For northern Wisconsin, shift the dates about 2 weeks later in spring and 2 weeks earlier in fall. This way, you’ll have fresh collards from June through November.
Companion Planting For Better Growth
Collards grow well with certain plants and poorly with others. Good companions include:
- Beets
- Celery
- Onions
- Potatoes
- Herbs like dill and chamomile
Avoid planting collards near:
- Other brassicas (cabbage, kale, broccoli) to reduce pest and disease pressure
- Strawberries
- Tomatoes
- Pole beans
Companion planting can help repel pests and improve soil health. For example, dill attracts beneficial insects that prey on cabbage worms.
When To Start Seeds Indoors
If you want an even earlier start, you can begin collard seeds indoors. Start them 4 to 6 weeks before your last frost date. For southern Wisconsin, that means starting seeds indoors around March 15 to April 1.
Use seed-starting mix in small pots or trays. Keep the soil moist and warm (70°F to 75°F). Once seedlings have two true leaves, harden them off by gradually exposing them to outdoor conditions over a week.
Transplant them outdoors after the last frost date, spacing them 12 to 18 inches apart. This method gives you a head start of about 2 to 3 weeks compared to direct sowing.
Fall Planting For Overwintering
In milder parts of Wisconsin (zones 5b and warmer), you can try overwintering collards. Plant them in late summer as usual, but instead of harvesting all the leaves, leave the plants in the ground. Mulch heavily with straw or leaves to protect the roots.
In early spring, the plants will start growing again. You’ll get an early harvest before the spring-planted collards are ready. This works best with cold-hardy varieties like Vates or Morris Heading.
Frequently Asked Questions
Q: Can I plant collard greens in Wisconsin in July?
A: Yes, but only for a fall harvest. Plant in mid-July to early August, depending on your region. This gives the plants time to mature before the first hard frost.
Q: What is the latest I can plant collard greens in Wisconsin?
A: For a fall crop, the latest is about 6 to 8 weeks before the first expected frost. In southern Wisconsin, that’s around mid-August. In northern areas, early August is the cutoff.
Q: Do collard greens survive winter in Wisconsin?
A: With heavy mulching and cold protection, some varieties can survive winter in milder parts of Wisconsin. However, most gardeners treat them as annuals and replant each year.
Q: How long does it take collard greens to grow in Wisconsin?
A: Most varieties take 60 to 80 days from seed to harvest. Transplants can cut that time by 2 to 3 weeks.
Q: Should I soak collard seeds before planting?
A: Soaking is not necessary. Collard seeds germinate quickly in moist soil. If you want to speed things up, soak them for 12 to 24 hours before planting.
Final Tips For Wisconsin Gardeners
Growing collards in Wisconsin is totally doable with a little planning. The most important thing is to respect the frost dates and plant at the right time. Keep an eye on the weather forecast and be ready to protect your plants from unexpected cold snaps.
Don’t forget to rotate your crops each year to avoid soil-borne diseases. And if you have extra space, try a few different varieties to see which ones perform best in your microclimate.
With the right timing and care, you’ll be enjoying fresh collard greens from your garden from early summer through late fall. Happy planting!