Cabbage in Zone 3B — Great Plains

Cabbage is a rewarding crop to grow here on the Plains. Its crisp texture and mild flavor are a welcome addition to slaws, soups, and stir-fries, especially since fresh produce can be scarce at times. Plus, there’s a real satisfaction in harvesting a sizable head of cabbage that you nurtured from a tiny seed, a welcome sight after our long winters.

Our extreme weather can be tough on plants, and cabbage is no exception. But with a bit of planning and attention to timing, you can definitely grow cabbage successfully within our 118-day growing season. Starting seeds indoors gives you a head start, allowing you to get a good harvest before the first frost hits.

Starting your cabbage indoors is the way to go here in the Plains to get a jump on our short growing season. Aim to sow your seeds mid-March through early April, about six weeks before you plan to transplant them outside. This timing allows the seedlings to develop into sturdy transplants.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist but not soggy, and provide warmth and plenty of light—a sunny south-facing window or grow lights work well. A trick I use is bottom watering: set the tray in a shallow dish of water and let the soil soak it up from the bottom. This helps prevent damping-off disease. Remember that spring can bring unexpected temperature swings, so keep an eye on your seedlings and adjust their environment as needed.

Transplant your cabbage seedlings outdoors early May through early June, once the danger of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Place them in a sheltered spot for a few hours each day, increasing the time as the week progresses.

When transplanting, space the plants 12-18 inches apart in rows. Choose a cloudy day for transplanting to minimize stress on the young plants. Our spring weather can be unpredictable, so keep an eye out for late frosts and be prepared to cover your plants if necessary.

Cabbage needs consistent moisture to thrive, but overwatering can be just as detrimental as underwatering, especially with our variable rainfall. A good rule of thumb is to water deeply once or twice a week, providing about 1-1.5 inches of water each time, depending on rainfall. The "finger test" is your friend: stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water.

During our hot summer months, you'll likely need to water more frequently. Watering at the base of the plants is preferable to overhead watering, as it reduces the risk of fungal diseases in our low-to-moderate humidity. However, in extended dry periods, a gentle overhead watering in the early morning can help cool the plants.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and root rot. Mulching around your cabbage plants with straw or wood chips helps retain moisture, suppress weeds, and regulate soil temperature, which is especially helpful during our hot summers and unexpected temperature swings. Consistent moisture prevents splitting, but heavy watering after a drought can cause heads to crack open.

Here in Zone 3B, you can expect your first cabbage harvest mid-July through early September, about 70 days after transplanting. The key is to watch for signs of ripeness. A ripe cabbage head will feel firm and solid when squeezed, indicating that it's tightly packed. Also, ensure the head has reached its full size for the specific variety you're growing.

To harvest, use a sharp knife to cut the cabbage head at its base, leaving a short stem attached. This prevents the head from splitting open. Cabbage doesn't ripen off the vine, so wait until it's truly ready before harvesting.

As the first frost approaches around mid-September, keep a close eye on the weather forecast. If a frost is predicted, you can harvest any remaining mature heads, even if they're not quite fully grown. Smaller heads can still be used in cooking.

Here are some common cabbage problems we face here in the Great Plains:

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves. You'll also see dark green droppings and white butterflies fluttering nearby.
• What causes it: These are the larvae of white cabbage butterflies. We can have multiple generations in a season if it stays warm enough.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent the butterflies from laying eggs. Handpick caterpillars when you see them. Interplanting with aromatic herbs like thyme and sage can also help deter them.

Cabbage Loopers

• What it looks like: Similar to cabbage worms, but loopers move in a distinctive "looping" motion. They also chew holes in leaves and can damage the developing heads.
• What causes it: Cabbage loopers are another type of caterpillar pest that thrives in warm weather.
• How to fix/prevent it: Use Bt spray. Handpick loopers. Encourage natural predators like parasitic wasps and lacewings.

Splitting

• What it looks like: The cabbage head cracks open, often after a period of heavy rain or inconsistent watering.
• What causes it: Rapid changes in soil moisture cause the head to swell too quickly, leading to splitting. This is especially common after a dry spell followed by heavy rainfall.
• How to fix/prevent it: Consistent watering is key. Mulch around the plants to help retain moisture. If heavy rain is expected, consider cutting a few roots to slow down water uptake.

Clubroot

• What it looks like: Stunted growth, wilting in the afternoon heat, and yellowing leaves. When you dig up the plant, the roots are swollen, distorted, and club-shaped.
• What causes it: A soil-borne pathogen (Plasmodiophora brassicae) that persists in the soil for many years. It favors acidic, wet soil.
• How to fix/prevent it: Raise the soil pH to 7.0-7.2 with lime. Improve drainage. Rotate brassicas on a 7-year cycle. Remove and destroy infected plants (don't compost them). Start transplants in a sterile mix.

Great Plains Specific Challenges: Our hot summers and variable rainfall can make it challenging to maintain consistent soil moisture for cabbage. Wind protection is essential, as strong winds can dry out the soil and stress the plants. Hail can also cause significant damage to cabbage leaves and heads, so consider using netting or row covers if hail is in the forecast.

Companion planting can be a useful strategy for growing cabbage here on the Plains. Green beans are good companions because they fix nitrogen in the soil, which benefits cabbage. Celery can deter cabbage white butterflies, while onions repel cabbage root flies. Potatoes can help break up the soil and improve drainage, and dill attracts beneficial insects that prey on cabbage pests.

Avoid planting cabbage near tomatoes, strawberries, and peppers. Tomatoes and peppers compete for the same nutrients, while strawberries can attract slugs that may also feed on cabbage.