Collard Greens in Zone 10B — Desert Southwest

Collard greens are a fantastic addition to any Desert Southwest garden, offering a slightly bitter, earthy flavor that's delicious braised, sautéed, or added to soups and stews. Here in Zone 10B, their mild frost tolerance means you can harvest fresh greens for a good portion of the year, especially if you time your plantings right to take advantage of our two growing seasons.

Our extreme heat and alkaline soil can present challenges, but collards are surprisingly adaptable. With careful attention to watering and timing your planting windows, you can enjoy a bountiful harvest of these nutritious greens throughout much of our 349-day growing season.

Starting collard greens indoors is an option, though not essential, for Desert Southwest gardeners. If you want a head start, especially for your spring crop, sow seeds indoors from mid-December through early January, about four weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and provide warmth and bright light – a sunny windowsill or grow lights work well. Bottom watering helps prevent damping-off; set the tray in a shallow dish of water and let the soil soak it up from the bottom. Given our very-early spring character, starting indoors can give you a jump on the season.

Transplant your collard green seedlings outdoors from mid-January through mid-February. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space the plants 18-24 inches apart to allow for good air circulation and growth. Keep an eye on the weather; while collards are frost-hardy, protect young transplants from any unexpected cold snaps with row covers or blankets.

Direct sowing collard greens is a simple and effective method for Desert Southwest gardens. Sow seeds directly into well-prepared soil from early January through early October, taking advantage of both our spring and fall growing seasons.

Ensure the soil is loose and the temperature is consistently above 50°F (10°C) for good germination. Plant seeds about ½ inch deep and space them 18-24 inches apart. Thin seedlings as they grow to ensure proper spacing and air circulation. Direct sowing is especially practical for fall crops, as it avoids the need for indoor setup during our warmer months.

Collard greens need consistent moisture to thrive, especially in our arid Desert Southwest climate. While more heat-tolerant than some other brassicas, they still need regular watering to prevent stress and ensure tender leaves.

During the cooler months (late fall through early spring), water deeply about once a week, providing roughly 1-1.5 inches of water. As temperatures rise in late spring and summer, increase watering to 2-3 times per week, ensuring the soil stays consistently moist. Use the finger test – stick your finger about 2 inches into the soil; if it feels dry, it's time to water.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our monsoon season. Signs of underwatering include wilting leaves and slow growth, while overwatering can lead to yellowing leaves and root rot. Mulching around the plants with organic materials like straw or wood chips helps retain moisture and regulate soil temperature.

You can expect your first harvest of collard greens from mid-March through early January, about 75 days after planting. Harvest the lower leaves when they are 10-12 inches long, leaving the top rosette intact to continue producing new leaves.

Look for leaves that are a deep green color and free from blemishes. To harvest, simply snap or cut the leaves off near the base of the plant. Collard greens are known to sweeten in flavor after a frost, so don't be afraid to leave some on the plant as late December approaches.

As the first frost nears, you can either harvest all remaining leaves or cover the plants to extend the harvest a bit longer. Continuous harvesting encourages the plant to keep producing throughout the growing season.

Here are some common problems you might encounter with collard greens in the Desert Southwest:

Cabbage Worms

• What it looks like: Smooth green caterpillars chewing irregular holes in leaves, leaving dark green droppings. White butterflies flying around your plants.
• What causes it: Larvae of white cabbage butterflies, which can have multiple generations in our long, warm growing season.
• How to fix/prevent it: Use Bt spray, which is very effective. Floating row covers can prevent the butterflies from laying eggs. Handpick caterpillars when you see them. Interplant with aromatic herbs like thyme and sage to deter the butterflies.

Aphids

• What it looks like: Clusters of tiny green, black, or white soft-bodied 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. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Knock them off with a strong spray of water. Encourage ladybugs and lacewings, which are natural predators. Use insecticidal soap for heavy infestations or neem oil for a systemic approach. Avoid excess nitrogen fertilizer.

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 a moth. They love brassicas.
• How to fix/prevent it: Same controls as for cabbage worms work for loopers. Bt is your friend. Row covers are effective.

Downy Mildew

• What it looks like: Yellow patches on leaf tops with fuzzy gray-purple growth on the undersides. Leaves brown and die from the bottom up.
• What causes it: An oomycete pathogen that spreads in cool, humid conditions via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by properly spacing plants. Water at the base, avoiding overhead watering. Copper-based fungicides can be used for prevention.

Desert Southwest Specific Challenges: The extreme heat of our summers can stress collard greens, making them more susceptible to pests and diseases. Arid conditions can also lead to sunscald, so providing afternoon shade with shade cloth is essential during the hottest months. The monsoon rainfall can create periods of high humidity, increasing the risk of fungal diseases like downy mildew. Proper watering and good air circulation are key to summer survival.

Companion planting can help your collard greens thrive in the Desert Southwest. Onions and garlic are great companions because their strong scent deters many pests. Beets and potatoes are also good choices, as they don't compete for the same nutrients in the soil. Dill attracts beneficial insects that prey on aphids and other pests.

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