Collard Greens in Zone 9A — Northern California

Collard greens thrive in our Northern California climate, offering a delicious and nutritious addition to your garden and kitchen. Their slightly bitter, earthy flavor is fantastic in Southern-inspired dishes, stir-fries, or even smoothies. Plus, you'll enjoy the satisfaction of harvesting fresh greens from your yard nearly year-round.

While we face challenges like drought and increasingly hot summers, collard greens are surprisingly resilient with the right timing and care. Our long growing season – roughly 288 days – gives you ample opportunity to grow them successfully, even with water restrictions.

Starting collard greens indoors gives you a head start, but it's not essential in our climate with such a long growing season. If you want to get a jump on things, aim to sow seeds indoors from mid January through early February, about four weeks before you plan to transplant. Use seed trays or small pots filled with a good seed-starting mix.

Keep the soil consistently moist (bottom watering works great to prevent damping off) and provide warmth with a heat mat if needed. Once seedlings emerge, ensure they get plenty of light – a sunny windowsill or grow lights will do the trick. Given our early springs, this method is more about personal preference than necessity.

Transplant your collard green seedlings outdoors from mid February through mid March, once they have a few sets of true leaves. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This acclimates them to the sun and wind, preventing shock.

Space your collard greens 18-24 inches apart in well-drained soil. Keep an eye on the weather during this time; those late-season cold snaps can still happen, so be ready to cover your seedlings if frost is predicted.

Direct sowing collard greens is a simple and effective method, especially in our mild Northern California climate. You can direct sow from early February through early September, giving you plenty of flexibility. Prepare your soil by loosening it and adding compost or other organic matter.

Sow seeds about ½ inch deep and space them 18-24 inches apart. Keep the soil consistently moist until the seedlings emerge. Direct sowing is a great option for a continuous harvest throughout the season.

Watering is crucial for healthy collard greens, especially during our dry summers. While more heat-tolerant than some brassicas, they still need consistent moisture to prevent tough, bitter leaves. Aim to keep the soil evenly moist, but not waterlogged.

During the cooler spring and fall months, you'll likely only need to water once or twice a week, providing about 1 inch of water each time. As temperatures rise in the summer, increase watering to 2-3 times per week, ensuring the soil is moist about 2 inches deep – use the "finger test" to check. Watering at the base of the plants is preferable to overhead watering, as it reduces the risk of fungal diseases in our low-humidity environment.

Signs of underwatering include wilting leaves and slow growth. Overwatering, on the other hand, can lead to yellowing leaves and root rot. Applying a layer of mulch around your collard greens helps retain moisture and suppress weeds, a definite plus during our hot, dry summers.

You can expect your first harvest of collard greens about 75 days after planting, which typically falls between late April and mid December in Northern California. Harvest the lower leaves when they are 10-12 inches long. Simply snap or cut them off near the base of the plant, leaving the top rosette to continue growing.

Harvesting in this way allows for continuous production throughout the season. Many gardeners find that the flavor of collard greens sweetens after a light frost, so don't be afraid to leave them in the garden a bit longer as temperatures drop in late fall. As our first frost approaches in early December, harvest any remaining large leaves to enjoy before the cold weather sets in.

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

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves, leaving dark green droppings behind. You might also see white butterflies fluttering around.
• What causes it: The larvae of white cabbage butterflies. They thrive in our warm climate and can have multiple generations per season.
• How to fix/prevent it: Bt spray is very effective. Floating row covers prevent butterflies from laying eggs. Handpick caterpillars when you see them 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 undersides of leaves. Sticky honeydew residue and curled or distorted new growth.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather. Ant colonies may even farm them.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings, their natural predators. Use insecticidal soap for heavy infestations and avoid excess nitrogen fertilizer.

Cabbage Loopers

• What it looks like: Similar to cabbage worms, but these are pale green caterpillars that move in a looping motion. They also chew holes in leaves.
• What causes it: The larvae of cabbage looper moths.
• How to fix/prevent it: Same as for cabbage worms: Bt spray, floating row covers, handpicking, and encouraging beneficial insects.

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves with fuzzy gray-purple growth on the undersides. Leaves brown and die from the bottom up.
• What causes it: This oomycete pathogen spreads in cool, humid conditions (which can occur even during our dry summers due to morning fog) via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation and water at the base, never overhead. Copper-based fungicides can help prevent it.

Northern California Specific Challenges: Our moderate-to-hot summers and dry-summer rainfall pattern mean you need to be vigilant about watering and pest control. While downy mildew isn't as prevalent as in more humid climates, it can still occur, especially in microclimates with poor air circulation. Drought conditions can stress plants, making them more susceptible to pests and diseases, so consistent watering and soil moisture management are essential.

Companion planting can benefit your collard greens in Northern California. Onions and garlic are excellent companions because their strong scent deters pests like aphids and cabbage moths. Beets and potatoes are also good choices as they don't compete for the same nutrients. Dill attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests.

Avoid planting collard greens near strawberries or tomatoes. Strawberries can attract slugs and snails, which may also feed on your collard greens. Tomatoes can harbor diseases that can spread to collards, so it's best to keep them separated.