Calendula in Zone 9B — Desert Southwest

Calendula is a fantastic addition to any Desert Southwest garden. The cheerful blooms bring a splash of color, plus the petals are edible and have medicinal properties. It's incredibly satisfying to grow something so beautiful and useful in our challenging climate.

Our extreme heat and alkaline soil can be tough, but Calendula thrives with the right timing. With our long, 313-day growing season, you'll have plenty of opportunities to enjoy these bright flowers.

Starting Calendula indoors is an option, but honestly, it's usually not necessary here in the Desert Southwest. Direct sowing is so easy, and Calendula seedlings don't mind being transplanted. However, if you want a super early start, aim to sow indoors from early to late December, about six weeks before our typical transplant window.

Use seed trays with good drainage and a seed-starting mix. Keep the soil consistently moist by bottom watering, setting the tray in a shallow dish of water until the surface is damp. Provide warmth and bright light. Remember, our spring comes early, so indoor starts need to be ready sooner than in other zones.

Transplant your Calendula seedlings outdoors from late January through early March. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock from our intense Desert Southwest sun.

Space plants 8-12 inches apart in well-draining soil. Keep an eye on the weather forecast. While Calendula is frost-hardy, a sudden cold snap can still stress young transplants. Provide temporary protection if needed.

Direct sowing Calendula is the easiest method in our climate. You can sow seeds directly into the garden from late January through mid October, giving you an incredibly long planting window.

Prepare the soil by loosening it and removing any rocks or debris. Calendula isn't too picky, but well-draining soil is key. Sow seeds about 1/4 inch deep and space them 8-12 inches apart. Keep the soil consistently moist until germination, which usually takes about a week.

Calendula needs moderate watering, especially when young and establishing. While it can tolerate some drought, consistent moisture encourages the best flowering. In the Desert Southwest, watering needs vary significantly with the seasons.

During the cooler months (late fall through early spring), water deeply once or twice a week, providing about 1 inch of water each time. Use the "finger test" – stick your finger into the soil about 2 inches deep. If it feels dry, it's time to water. During our monsoon season, watch the rainfall and adjust accordingly. Avoid overhead watering, as it can encourage fungal diseases in our arid climate. Instead, water at the base of the plant.

During the extreme heat of summer, Calendula may go dormant and need less water. Water deeply but less frequently, perhaps every 7-10 days, allowing the soil to dry out slightly between waterings. Signs of underwatering include wilting leaves and dry, crispy edges. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, like compost or shredded bark, helps retain moisture and keep the soil cool.

Deadheading is essential for continuous blooming with Calendula. Regularly remove spent flowers to encourage the plant to produce more. Simply snip off the flower head just below the bloom.

During the main growing season (spring and fall), deadhead as needed, every few days or once a week. Towards the end of the season, as the first frost approaches around mid- December, you can leave some flowers to mature and self-seed for the following year.

You can expect your first Calendula harvest about 45 days after planting, so early March for those early sowings. Harvest flowers when they are fully open, ideally in the morning after the dew has dried.

Gently snip the flower heads off the stem, leaving a short piece of stem attached. The petals are the most commonly used part, but the entire flower head is edible. To encourage continued production, harvest regularly. As the first frost approaches in mid- December, harvest any remaining flowers.

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

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Various fungi thrive in warm days, cool nights, and moderate humidity, which we can experience during our monsoon season. Dry leaf surfaces actually favor it.
• 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) is surprisingly effective.

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations explode in warm weather. Ant colonies may farm them for honeydew.
• How to fix/prevent it: Strong water spray knocks them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap for heavy infestations. Neem oil works systemically. Avoid excess nitrogen fertilizer (it attracts them).

Whiteflies

• What it looks like: Tiny white, moth-like insects that fly up when disturbed. Yellowing or silvering of leaves. Sticky honeydew residue.
• What causes it: Sap-sucking insects that thrive in warm, dry conditions. They can quickly infest plants in our arid Desert Southwest climate.
• How to fix/prevent it: Yellow sticky traps can help capture adult whiteflies. Strong water sprays knock them off. Insecticidal soap or neem oil are effective treatments. Reflective mulch can deter them.

Desert Southwest Specific Challenges: Our extreme heat and low humidity can stress Calendula, making it more susceptible to pests and diseases. Provide afternoon shade during the hottest months and ensure adequate watering. Alkaline soil is usually not a problem, but consider amending with compost to improve drainage and nutrient availability.

Calendula makes a great companion plant in the Desert Southwest garden.

• Tomato and Pepper: Calendula attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests that often plague tomatoes and peppers.
• Green Beans: Calendula can help deter bean beetles, which can be a problem during our warmer months.

Avoid planting Calendula near plants that are susceptible to powdery mildew, as it can potentially spread the disease.