Calendula in Zone 10B — Desert Southwest

Calendula is a fantastic addition to any Desert Southwest garden. Its bright, cheerful flowers add beauty to your landscape, and the petals are edible, adding a peppery kick to salads. Plus, the satisfaction of using your own homegrown petals in soothing skin salves is hard to beat, especially after a long day dealing with our intense sun.

Our extreme heat and alkaline soil can be challenging, but with proper timing, Calendula thrives here. You can take advantage of our long, 349-day growing season and enjoy blooms for months.

Starting Calendula indoors is possible, but often not necessary in our climate. Given our very-early spring character and long growing season, direct sowing usually works just fine. If you want a head start, though, you can sow seeds indoors from mid-November through early December, about six weeks before you'd like to transplant them.

Use seed trays with a good seed-starting mix. Keep them warm (around 70°F) and provide plenty of light – a simple grow light works wonders. Bottom watering helps prevent damping-off, a common problem with seedlings.

Transplant your Calendula seedlings outdoors from early January through mid-February. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents transplant shock.

Space them 8-12 inches apart in a sunny or partially shaded spot. Keep an eye on the weather; an unexpected cold snap can still occur, so be prepared to cover them if needed.

Direct sowing Calendula is a simple and effective method in our region. You can sow seeds directly into the garden from early January through early November. The soil temperature needs to be at least 55°F for germination.

Prepare the soil by loosening it and adding compost. Sow seeds about ¼ inch deep and keep the soil consistently moist until they germinate. Thin seedlings to 8-12 inches apart once they emerge.

Calendula needs moderate watering, but it's crucial to get it right in our desert climate. During the cooler months (early spring and late fall), water deeply once or twice a week, providing about 1 inch of water each time. Use the "finger test" – if the top 2 inches of soil are dry, it's time to water.

As the weather heats up, especially during our monsoon season, increase watering to 2-3 times a week, ensuring the soil doesn't dry out completely. However, avoid overhead watering, as this can encourage fungal diseases in our humid monsoon conditions. Water at the base of the plants.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, indicated by yellowing leaves and a mushy stem base. A layer of organic mulch around the base of the plants helps retain moisture and regulate soil temperature.

Deadheading is key to keeping your Calendula blooming continuously. Regularly remove spent flowers to encourage new buds to form. Simply pinch or snip off the flower heads just below the bloom.

During the peak heat of summer, Calendula may slow down or even go dormant. Continue deadheading to keep the plants tidy, but don't expect as many blooms. As the weather cools in late fall, resume regular deadheading to encourage a final flush of flowers. Before our first frost (around late December), you can let some flowers mature and dry on the plant if you want them to self-seed for the following year.

You can expect your first Calendula harvest about 45 days after planting. In our region, that means from mid-February onward for a spring planting, or late fall for a fall planting. Harvest the flowers when they are fully open, ideally in the morning after the dew has dried.

Gently pluck the entire flower head from the plant. For continued production, harvest regularly, as this encourages more blooms.

As the first frost approaches in late December, harvest any remaining flowers to dry for later use. You can also let some flowers go to seed if you want a volunteer crop next year.

Here are three common problems you might encounter with Calendula in the Desert Southwest:

Powdery Mildew

• What it looks like: A white or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Fungal disease favored by warm days, cool nights, and surprisingly, dry leaf surfaces. Our arid climate can actually make it more prevalent.
• How to fix/prevent it: Improve air circulation by spacing plants properly. Remove affected leaves promptly. Apply neem oil or potassium bicarbonate sprays. Milk spray (1 part milk to 9 parts water) can also be effective.

Aphids

• What it looks like: Clusters of tiny green, black, or white insects on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Sap-sucking insects that thrive in warm weather. Ant colonies often protect them.
• How to fix/prevent it: Blast them off with a strong stream of water. Encourage beneficial insects like ladybugs and lacewings. Use insecticidal soap or neem oil for heavy infestations. Avoid over-fertilizing with nitrogen.

Whiteflies

• What it looks like: Tiny white, moth-like insects that fly up when disturbed. Yellowing or silvering of leaves. Sticky honeydew.
• What causes it: Sap-sucking insects that love warm, dry conditions. They multiply rapidly in our desert heat.
• How to fix/prevent it: Hang yellow sticky traps to catch adults. Spray with insecticidal soap or neem oil, paying close attention to leaf undersides. Ensure good air circulation.

Desert Southwest Specific Challenges: Our extreme heat and low humidity can stress Calendula, making them more susceptible to pests and diseases. Provide afternoon shade during the hottest months and ensure adequate watering. While monsoon moisture can be beneficial, it also creates conditions that favor fungal diseases, so good air circulation is crucial.

Calendula makes a great companion plant in the Desert Southwest garden. Planting them near tomatoes and peppers can help deter pests like tomato hornworms and aphids. They also attract beneficial insects that pollinate these crops.

Green beans also benefit from having Calendula nearby. The flowers attract pollinators, leading to better bean production. There aren't any widely known bad companions for Calendula, so feel free to experiment and see what works best in your garden.