Calendula in Zone 9A — Desert Southwest

Calendula is a fantastic addition to any Desert Southwest garden. Its cheerful blooms brighten the landscape, the petals add a peppery zing to salads, and it's incredibly versatile for homemade skincare. Plus, you’ll get the satisfaction of growing something beautiful and useful in our challenging climate.

Don't let our extreme heat scare you off! With careful timing, especially planting during our two growing seasons, you can enjoy calendula from spring through fall. Our 298-day growing season gives you plenty of opportunity to succeed.

Starting calendula indoors is an option, especially if you're eager to get a very early start. Sow seeds indoors from mid December through early January, about six weeks before you plan to transplant. This gives you a head start before the heat really kicks in.

Use seed trays with a good seed-starting mix and keep them warm and well-lit, using grow lights if needed. Bottom watering helps keep the soil evenly moist without damping off. Remember, our spring character is very-early, so this indoor jump can make a real difference.

Transplant your calendula seedlings outdoors from early February through mid March. This allows them to get established before our extreme heat arrives. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space them 8-12 inches apart in a sunny spot with well-draining soil. Keep an eye on the weather forecast – those early months can still bring unexpected cold snaps, so be ready to cover your seedlings if needed.

Direct sowing is a simple and effective way to grow calendula in our region. Sow seeds directly into the garden from early February through mid October. This wide window takes advantage of both of our growing seasons.

Prepare the soil by loosening it and removing any rocks or debris. Calendula prefers slightly cooler soil, so avoid sowing during the hottest parts of the summer. Space seeds 8-12 inches apart and keep the soil consistently moist until they germinate.

Calendula needs moderate watering to thrive, but it's not very drought-tolerant, so don't neglect it. During our mild spring and fall, water deeply about once a week, providing around 1 inch of water. Use the finger test: if the top two inches of soil feel dry, it's time to water.

In the extreme heat of summer, you'll likely need to water more frequently, possibly every other day, especially if the monsoon moisture is scarce. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases even in our arid climate.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to root rot, indicated by yellowing leaves and a mushy stem base. Mulching around your calendula plants with a layer of organic matter like compost can help retain moisture and keep the soil cool.

Regular deadheading is key to keeping your calendula plants blooming prolifically throughout the season. Simply pinch or snip off the spent flowers just below the flower head. This encourages the plant to produce more blooms instead of setting seed.

Leave some flowers to mature towards the end of the season if you want them to self-seed for next year. As our first frost approaches in early December, you can let the remaining flowers go to seed, or harvest them for medicinal or culinary use.

You can expect your first calendula harvest about 45 days after planting, usually from mid March through mid December in our Zone 9A climate. Harvest the flowers when they are fully open and at their peak color.

To harvest, simply snip off the flower heads near the base of the stem. Harvest in the morning after the dew has dried for the best flavor and medicinal properties. Regular harvesting encourages continued blooming.

As the weather cools down in late fall, you can continue to harvest flowers until the first frost. You can dry the petals for later use or use them fresh in teas, salads, and skincare products.

Here are some common problems you might encounter with calendula in our Desert Southwest gardens:

Powdery Mildew

• What it looks like: 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 moderate humidity. It's ironic, but dry leaf surfaces can actually make it worse.
• How to fix/prevent it: Improve air circulation by spacing plants properly and pruning. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help. A 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 and curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations can explode during our warm spring weather.
• How to fix/prevent it: Knock them off with a strong spray 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 leaves, sticky honeydew.
• What causes it: Sap-sucking insects that thrive in warm, dry conditions. Common in our desert climate.
• How to fix/prevent it: Use yellow sticky traps to catch adults. Spray with insecticidal soap or neem oil, paying attention to the undersides of leaves. Keep plants well-watered and healthy.

Desert Southwest Specific Challenges: The extreme heat and low humidity stress in our region can weaken calendula plants, making them more susceptible to pests and diseases. Monitor your plants closely and provide adequate water and shade during the hottest parts of the summer. Our monsoon season can also bring humidity spikes that encourage powdery mildew, so ensure good air circulation.

Calendula makes a wonderful companion plant for many vegetables in our Desert Southwest gardens. Plant it near tomatoes and peppers to attract pollinators and beneficial insects that prey on pests. The strong scent can also help deter tomato hornworms and other unwanted visitors.

Calendula also works well planted near green beans. It attracts pollinators to help increase bean production. Avoid planting calendula near members of the cabbage family (broccoli, cauliflower, kale) as it can attract cabbage moths and other pests that also target these crops.