Cabbage in Zone 4A — Great Plains

Cabbage might just be the most rewarding cool-season crop you can grow here on the Plains. There's nothing like the taste of a fresh, crisp head of cabbage in a summer slaw, and it's incredibly versatile in the kitchen. Plus, seeing those tightly packed heads develop in your garden is just plain satisfying.

Our extreme weather can be a challenge, with those temperature swings and the risk of hail. But with a little planning, we can definitely grow some great cabbage during our 138-day growing season. Timing is everything, and starting indoors gives us a head start.

Starting cabbage indoors is the way to go for a good spring harvest here. You'll want to get those seeds going in early to late March, about six weeks before you plan to transplant them outside. Spring here can be so variable; starting indoors gives you more control.

Use seed trays or small pots filled with a good seed-starting mix. Keep them warm – around 70°F – and provide plenty of light, either with a grow light or a very sunny window. Don't forget to water them from the bottom to encourage strong root growth and prevent damping-off.

Transplant your cabbage seedlings outdoors in late April through late May once the soil has warmed up a bit. Before planting, you'll need to harden them off. Give them a week of gradual exposure to the outdoors, increasing the amount of time they spend outside each day.

Space your plants about 12-18 inches apart in a spot that gets full sun. Keep an eye on the weather forecast around transplant time – a late frost can still happen, so be ready to cover your seedlings if needed.

Cabbage needs consistent moisture to thrive, but overwatering can be just as bad as underwatering, especially with our variable rainfall here on the Plains. Aim for about 1 inch of water per week, either from rain or irrigation.

The best way to tell if your cabbage needs water is to use the "finger test." Stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Water deeply at the base of the plant rather than overhead, if possible. This helps to prevent fungal diseases, which can be a concern even with our low-to-moderate humidity.

In the heat of summer (typical high: 93°F), you might need to water more frequently. Underwatering can cause the heads to be small and bitter, while heavy watering after a dry spell can cause the heads to split open. Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot.

A layer of mulch around your cabbage plants will help to retain moisture and keep the soil cool, which is especially important during our hot summers. Straw or grass clippings work well.

You can expect your first cabbage harvest in early July through late August, about 70 days after transplanting. The key to knowing when to harvest is to check the firmness of the head.

Give the head a gentle squeeze. If it feels firm and solid, it's ready to harvest. Also, check that the head has reached the full size expected for the variety you're growing. To harvest, simply cut the head off at the base with a sharp knife.

As our first frost approaches in late September, harvest any remaining heads, even if they're not quite fully mature. They'll store better if harvested before a frost.

Here are some common problems you might encounter growing cabbage on 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 around.
• What causes it: These are the larvae of those pretty white cabbage butterflies. They can have multiple generations throughout the season, especially during warmer summers.
• How to fix/prevent it: Bt spray (Bacillus thuringiensis) is very effective. Floating row covers keep the butterflies from laying eggs. You can also handpick the caterpillars and encourage parasitic wasps to visit your garden. Interplanting with aromatic herbs like thyme and sage can help deter the butterflies.

Cabbage Loopers

• What it looks like: Similar to cabbage worms, but these caterpillars move with a distinctive looping motion. They also chew holes in leaves and leave behind droppings.
• What causes it: Cabbage loopers are a different species of caterpillar that also loves to feed on brassicas. Like cabbage worms, they thrive in warm weather.
• How to fix/prevent it: Bt spray works well on cabbage loopers too. Handpicking is also effective. Encourage beneficial insects like lacewings and parasitic wasps.

Splitting

• What it looks like: The cabbage head cracks open.
• What causes it: Inconsistent watering. A sudden influx of water after a dry period causes the head to grow too quickly, splitting the outer leaves. This is especially common here with our variable rainfall.
• How to fix/prevent it: Maintain consistent soil moisture. Water deeply and regularly, especially during dry spells. Mulching helps to retain moisture and prevent rapid fluctuations in soil moisture. Harvest heads as soon as they are mature to prevent them from splitting.

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 can persist in the soil for 10+ years. It thrives in acidic, wet soil.
• How to fix/prevent it: Raise the soil pH to 7.0-7.2 with lime. Improve drainage. Rotate your brassicas on a 7-year cycle. Remove and destroy infected plants (don't compost them). Start your transplants in a sterile mix to avoid introducing the pathogen.

Great Plains Specific Challenges: The hot summer heat can stress cabbage plants, making them more susceptible to pests and diseases. Variable rainfall can lead to splitting. Wind protection is essential to prevent windburn and keep plants from drying out.

Companion planting can be a great way to improve your cabbage crop here on the Plains.

Good companions include green beans, celery, onions, potatoes, and dill. Green beans fix nitrogen in the soil, which benefits cabbage. Celery deters cabbage white butterflies. Onions and dill repel many common cabbage pests. Potatoes don't directly benefit cabbage, but they don't compete for resources and can help break up the soil.

Avoid planting cabbage near tomatoes, strawberries, and peppers. Tomatoes and peppers can attract similar pests, increasing the risk of infestation. Strawberries compete for resources and can stunt the growth of cabbage.