Collard Greens in Zone 8A — Northern California

Collard greens are a fantastic addition to any Northern California garden. Their slightly bitter, earthy flavor is delicious in Southern-style cooking, stir-fries, or even raw in salads when young. Plus, they thrive in our long growing season and even benefit from a touch of frost, which sweetens their flavor.

We NorCal gardeners know about drought, fire season, and the wildly varying microclimates around the Bay. But don't let that deter you! Collard greens are surprisingly resilient, and with a little planning and attention to watering, you can enjoy a bountiful harvest throughout our 255-day growing season.

Starting collard greens indoors in early to late February, about four weeks before transplanting, is certainly an option, especially if you're aiming for an extra-early harvest. It's not strictly necessary in our climate, but it gives you a head start.

If you choose to start indoors, use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist, using bottom watering to avoid disturbing the seedlings. Provide warmth and plenty of light, either from a sunny windowsill or a grow light. With our early springs, indoor starting helps bypass any late cold snaps we sometimes get.

Transplant your collard green seedlings outdoors from early March through early April, once they have a few sets of true leaves. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space your transplants 18-24 inches apart in well-drained soil. Keep an eye on the weather forecast, as we can still get some unpredictable cool spells during this time. A frost blanket can be helpful if temperatures dip unexpectedly low.

Direct sowing collard greens is a straightforward and effective method for us here in Northern California. You can sow seeds directly into the garden from late February through late August, giving you plenty of flexibility.

Prepare the soil by loosening it and amending with compost. Plant seeds about ½ inch deep and keep the soil consistently moist until germination. Thin seedlings to 18-24 inches apart once they emerge. Direct sowing is great because you don’t have to worry about disturbing the roots with transplanting, but it does mean you'll need to be diligent about watering and protecting young seedlings from pests.

Watering is key to successful collard green growing, especially during our dry summers. While more heat-tolerant than some brassicas, they still need consistent moisture to produce tender leaves. In general, aim for about 1-1.5 inches of water per week, increasing this during hotter periods.

The "finger test" is your best friend: stick your finger about two inches into the soil near the base of the plant. If it feels dry, it's time to water. Water deeply at the base of the plant, avoiding overhead watering which can encourage fungal diseases in our Mediterranean climate.

During the cooler spring and fall months, you may only need to water once or twice a week. In the heat of summer, especially inland, you might need to water every other day. Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A layer of mulch around the plants helps retain moisture and suppress weeds.

You can expect your first harvest of collard greens from early May through late November, about 75 days after planting. The best time to harvest is when the lower leaves are 10-12 inches long.

Harvest by cutting the outer leaves near the base of the plant, leaving the top rosette to continue growing. This allows for continuous harvesting throughout the season. The flavor of collard greens actually 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, harvest any remaining large leaves. You can also cover the plants with a frost blanket to extend the harvest a bit longer.

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. You might also see white butterflies fluttering around.
• What causes it: These are the larvae of white cabbage butterflies, which lay their eggs on brassica plants. They can have multiple generations in our long, warm growing season.
• How to fix/prevent it: Bt spray is highly effective. Floating row covers can prevent the butterflies from laying eggs in the first place. Handpick caterpillars whenever you see them. Interplanting with aromatic herbs like thyme and sage can also help deter them.

Aphids

• What it looks like: Clusters of tiny green, black, or white soft-bodied insects on stems and undersides of leaves. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Aphids are sap-sucking insects that reproduce rapidly, especially in warm weather. Ants often "farm" them for their honeydew.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage ladybugs and lacewings, which are natural predators. Insecticidal soap is effective for heavy infestations. Neem oil can also work. Avoid over-fertilizing with nitrogen, as this attracts aphids.

Cabbage Loopers

• What it looks like: Similar to cabbage worms, but these caterpillars move in a looping motion. They also chew holes in leaves.
• What causes it: These are the larvae of moths. Like cabbage worms, they thrive in warm weather.
• How to fix/prevent it: Use Bt spray, handpick them, and use floating row covers. The same strategies for cabbage worms work well.

Downy Mildew

• What it looks like: Yellow patches on the upper surface of leaves, with fuzzy gray-purple growth on the undersides. Leaves may brown and die, starting from the bottom of the plant.
• What causes it: This is a fungal disease that spreads in cool, humid conditions via wind-borne spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants properly. Water at the base of the plant, avoiding overhead watering. Copper-based fungicides can be used preventatively.

Northern California Specific Challenges: Our moderate-to-hot, dry summers can stress collard greens, making them more susceptible to pests and diseases. Consistent watering is crucial. While downy mildew isn't as prevalent as in more humid climates, it can still occur during our cooler, foggy periods.

Companion planting can be a great way to improve the health and productivity of your collard greens. Onions and garlic are good companions because their strong scent can deter many pests. Beets and potatoes also work well, as they don't compete for the same nutrients in the soil. Dill attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests.

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