Calendula in Zone 7A — Mountain West

Calendula is a fantastic addition to any Mountain West garden. Its bright, cheerful flowers add beauty to your space, and the petals are edible, bringing a slightly peppery flavor to salads and other dishes. Plus, Calendula has medicinal properties, making it a truly versatile plant for our high-altitude gardens.

Our short growing season and intense sun can be challenging, but Calendula's relatively quick 45-day maturity makes it a winner. With a 173-day growing season, you have ample time to enjoy its blooms, especially with a little planning.

Starting Calendula indoors is definitely an option here in the Mountain West, especially if you want a head start on the season. Begin in mid-February through early March, about six weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and provide warmth and plenty of light.

Bottom watering is key to prevent damping off. Place the tray in a shallow dish of water and let the soil soak it up from the bottom. Given our late springs, starting indoors buys you some extra time.

Transplant your Calendula seedlings outdoors in early April through mid-May, once the danger of hard frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. Start with an hour or two of shade and increase the time and sun exposure each day.

Space the plants 8-12 inches apart to allow for good air circulation. Keep an eye on overnight temperatures, as we can still get some chilly nights even in April.

Direct sowing Calendula is a simple and effective method in our region. Sow seeds directly into the garden from early April through mid-August. Calendula seeds germinate best when the soil temperature is around 65-70°F.

Prepare the soil by loosening it and adding compost. Plant seeds 1/4 inch deep and space them 8-12 inches apart. Direct sowing is less work than starting indoors, but you'll need to protect the seedlings from late frosts and potential hail.

In the Mountain West, moderate watering is key for Calendula. While it can tolerate some drought, it prefers consistent moisture, especially during its peak blooming period. However, be careful not to overwater, as our alkaline soil doesn't drain as well as it could.

During the spring, water deeply about once a week, providing around 1 inch of water. Use the finger test: if the top 2 inches of soil feel dry, it's time to water. In the hotter, drier summer months, you might need to increase watering to two or three times a week. Watering at the base of the plant is best, as our low humidity minimizes the risk of fungal diseases.

Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, like shredded bark or wood chips, can help retain moisture and regulate soil temperature, which is beneficial during our hot days and cool nights.

Regular deadheading is essential for continuous blooming of Calendula. Throughout the season, remove spent flowers as soon as they start to fade. This encourages the plant to produce more blooms rather than putting energy into seed production.

Simply pinch or cut off the flower head just below the base of the flower. As the first frost approaches in early October, you can let some of the last flowers mature and go to seed if you want them to self-sow for the following year. Otherwise, clear the plants to prevent any potential disease issues over the winter.

Expect your first Calendula harvest about 45 days after planting, usually from late May through mid-October in our region. Harvest the flowers when they are fully open and the petals are at their peak color. The petals are most flavorful and have the highest medicinal properties at this stage.

To harvest, simply snip off the flower heads with scissors or pruning shears. Be careful not to damage the surrounding foliage. Regular harvesting encourages the plant to produce more flowers, extending your harvest window. As the season winds down and frost threatens, harvest all remaining flowers, even if they aren't fully open. You can dry them indoors for later use.

Here are some common problems you might encounter with Calendula in the Mountain West:

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves and stems. Leaves may curl, yellow, and die.
• What causes it: Fungi thrive in warm days, cool nights, and moderate humidity. Interestingly, dry leaf surfaces favor it, which can happen even with our low humidity if the plants are too crowded.
• 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. Milk spray (1 part milk to 9 parts water) is also effective.

Aphids

• What it looks like: Clusters of tiny insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue. Curled or distorted new growth.
• What causes it: Rapidly reproducing sap-sucking insects. Populations explode in warm weather.
• How to fix/prevent it: A strong water spray can knock them off. Encourage ladybugs and lacewings (natural predators). Insecticidal soap works well. Neem oil works systemically. Avoid over-fertilizing with nitrogen, as it attracts them.

Whiteflies

• What it looks like: Tiny white insects that fly up when disturbed. Yellowing or stippled leaves. Sticky honeydew residue.
• What causes it: Sap-sucking insects that thrive in warm conditions. They are often found on the undersides of leaves.
• How to fix/prevent it: Sticky traps can catch adult whiteflies. Strong water sprays can dislodge them. Insecticidal soap or neem oil are effective treatments. Encourage natural predators like lacewings and parasitic wasps.

Mountain West Specific Challenges: Our moderate-at-altitude heat, combined with low humidity and dry rainfall, can create conditions favorable for powdery mildew if air circulation is poor. While aphids and whiteflies can be issues, the dry air often keeps their populations somewhat in check compared to more humid regions. The intense UV light can also stress plants, making them more susceptible to pests and diseases, so ensure adequate watering and afternoon shade if possible.

Calendula makes excellent companions for several plants in the Mountain West garden. Plant them near tomatoes and peppers to help deter pests like tomato hornworms and aphids. Calendula attracts beneficial insects, such as ladybugs and lacewings, which prey on these pests.

Green beans also benefit from Calendula's presence, as it can help repel bean beetles. Avoid planting Calendula near members of the cabbage family (broccoli, cauliflower, kale), as they can attract cabbage moths.