Collard Greens in Zone 7B — Northern California

Collard greens are a fantastic addition to any Northern California garden. Their slightly bitter, earthy flavor is delicious in soups, stews, and stir-fries, and they provide a steady supply of nutritious greens throughout our long growing season. Plus, they thrive in our Mediterranean climate, offering a rewarding gardening experience.

Our dry summers and occasional water restrictions can be a challenge, but with smart planning, collard greens can flourish. Our 245-day growing season gives you plenty of time to get multiple harvests. You'll find that collard greens are quite adaptable when given the right care.

Starting collard greens indoors is an option, especially if you're eager to get a head start on the season. Begin in early February through early March, about four weeks before you plan to transplant them outside. This is particularly useful if you want larger plants ready to go as soon as the weather warms up.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist by watering from the bottom to avoid damping off – set the tray in a shallow pan of water and let the soil absorb it. Place the trays in a warm spot and under grow lights until seedlings emerge. Our early spring can have temperature swings, so indoor starting gives you more control.

Transplant your collard greens seedlings outdoors in mid March through mid April, once the danger of hard frost has passed. Before transplanting, harden off the seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sunlight and temperatures.

When transplanting, space the plants 18-24 inches apart to give them room to grow. Choose a spot with full sun to partial shade. While we often have sunny days, the partial shade can help prevent bolting as the weather warms.

Direct sowing is a straightforward method for growing collard greens, and it works well in our Northern California climate. Sow seeds directly into the garden from early March through mid August. This extended window allows for multiple plantings, ensuring a continuous harvest.

Prepare the soil by loosening it and mixing in compost or other organic matter. Ensure the soil temperature is at least 60°F for good germination. Plant seeds about ½ inch deep and space them 18-24 inches apart. Thin seedlings as needed once they emerge. Direct sowing is less work, but you'll need to be diligent about watering, especially in our dry summers.

Consistent watering is key to growing tender, flavorful collard greens in our Mediterranean climate. While they're more heat-tolerant than some other brassicas, our hot, dry summers mean they still need regular moisture. Aim to keep the soil consistently moist, but not waterlogged.

During the cooler spring and fall months, water deeply about once a week, providing about 1 inch of water. In the heat of summer, increase watering to two or three times a week, ensuring they get 1-1.5 inches of water each time. Use the "finger test" – stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal diseases in our microclimates, especially where morning fog is common.

Signs of underwatering include wilting leaves and slow growth. Overwatering can lead to yellowing leaves and root rot. Mulching around the plants with straw or wood chips helps retain moisture and regulate soil temperature, which is particularly beneficial during our hot summers.

You can expect your first harvest of collard greens in mid May through late November, about 75 days after planting. The best time to harvest is when the lower leaves are 10-12 inches long. These leaves will be the most mature and flavorful.

Harvest by cutting or snapping off the outer leaves, leaving the top rosette intact. This allows the plant to continue producing new leaves throughout the growing season. The flavor of collard greens often sweetens after a light frost, so don't be afraid to leave them in the garden as the weather cools.

As our first frost approaches in mid- November, you can harvest the entire plant if you wish. Alternatively, cover the plants with a frost blanket to extend the harvest a bit longer.

Here are some common problems you might encounter growing collard greens in Northern California:

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves, leaving dark green droppings. You might also see white cabbage butterflies fluttering around.
• What causes it: Larvae of white cabbage butterflies, which have multiple generations per season in our warm climate.
• How to fix/prevent it: Bt spray is very effective. Use floating row covers to prevent butterflies from laying eggs. Handpick caterpillars and interplant with aromatic herbs like thyme and sage.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects that thrive in warm weather.
• How to fix/prevent it: Strong water spray to knock them off. Encourage ladybugs and lacewings. Use insecticidal soap for heavy infestations and avoid excess nitrogen fertilizer.

Cabbage Loopers

• What it looks like: Pale green caterpillars that move in a looping motion. They chew large, irregular holes in leaves.
• What causes it: Similar to cabbage worms, these are the larvae of moths that lay eggs on the plants.
• How to fix/prevent it: Handpick the loopers. Use Bt spray or introduce parasitic wasps to control the population.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on undersides. Leaves brown and die from the bottom up.
• What causes it: An oomycete pathogen that spreads in cool, humid conditions.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation and water at the base of the plants. Use copper-based fungicides for prevention.

Northern California Specific Challenges: Our moderate-to-hot summers and low humidity can stress collard greens if they're not watered consistently. Dry conditions can also make them more susceptible to pests like aphids. Proper watering, mulching, and regular monitoring are crucial for success.

Companion planting can help your collard greens thrive in Northern California.

Good companions include onions and garlic, whose strong scents deter pests like cabbage moths and aphids. Beets and potatoes are also good neighbors, as they don't compete for the same nutrients and can improve soil health. Dill attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests.

Avoid planting collard greens near strawberries and tomatoes. Strawberries can attract slugs and snails, which can also damage collard greens. Tomatoes can stunt the growth of collard greens.