Calendula in Zone 5B — Mountain West

Calendula is a must-grow for any Mountain West gardener looking for beauty and function. Its vibrant flowers add a splash of color to your garden, and the petals are edible, adding a peppery zing to salads. Plus, calendula's medicinal properties are well-known, making it a versatile addition to your high-altitude garden.

Our short growing season and intense sun can be challenging, but calendula is surprisingly adaptable. With a 149-day growing season, you'll find that calendula fits right in. Careful timing lets you enjoy its blooms from early summer right up until our first frosts arrive.

Starting calendula indoors in our region is possible, but not always necessary. Since calendula handles frost, direct sowing often works just fine. However, starting indoors gives you a head start, especially if you're aiming for an early bloom.

If you opt to start indoors, sow seeds early to late March, about six weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and keep them in a warm spot with plenty of light. Remember to bottom water your seedlings to encourage strong root growth in our dry climate. Considering our late springs, this can give you a jump on the season.

Transplanting calendula outdoors in the Mountain West should happen late April through early June, once the risk of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to our intense UV and fluctuating temperatures.

Plant seedlings 8-12 inches apart in well-drained soil. Keep an eye on the weather forecast, as late spring can still bring unexpected cold snaps and even hail. Be ready to cover your young plants if needed.

Direct sowing calendula is a simple and effective method for Mountain West gardeners. You can direct sow from late April through early August, giving you a long window to get seeds in the ground. Direct sowing avoids transplant shock and lets the plants establish strong roots.

Prepare your soil by loosening it and removing any rocks or debris. Plant seeds about ½ inch deep and 8-12 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. Direct sowing is great because you can succession sow every few weeks for continuous blooms.

Calendula needs moderate watering, which can be tricky in our dry Mountain West climate. While it can tolerate some drought, consistent moisture encourages the best blooms. However, avoid overwatering, especially in our alkaline soil, as it can lead to root rot.

During the spring and fall, when temperatures are cooler, water deeply about once a week, providing about 1 inch of water. Use the finger test: stick your finger about 2 inches into the soil. If it feels dry, it's time to water. In the hotter summer months, you might need to water every few days, especially if we're experiencing a dry spell. Water at the base of the plant to avoid wetting the foliage, which helps prevent powdery mildew in our low-humidity environment.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and a mushy stem base. Applying a layer of mulch around your calendula plants helps retain moisture and regulate soil temperature, reducing the need for frequent watering.

Pruning calendula is easy and essential for continuous blooming in our short season. The key is to deadhead regularly. This means removing spent flowers as soon as they start to fade.

Pinch off the flower heads just below the bloom, encouraging the plant to produce more flowers rather than setting seed. Do this throughout the growing season, from early summer until our first frost in early October. If you want calendula to self-seed, leave a few flowers to mature and dry at the end of the season.

Harvesting calendula in the Mountain West can start as early as early June and continue through early October. Expect your first harvest about 45 days after planting, whether you started indoors or direct-sowed. The best time to harvest is when the flowers are fully open, ideally in the morning after the dew has dried.

Gently pinch or cut the flower heads from the stem, leaving a short stub. Harvest regularly to encourage continuous blooming. The petals are what you're after, so you can either pluck them off the flower head or dry the entire flower for later use.

As the first frost approaches, harvest all remaining flowers, even the ones that aren't fully open. These can still be dried and used. By harvesting regularly and strategically, you can maximize your calendula yield in our short growing season.

Calendula is generally easy to grow, but here are a few common problems you might encounter in the Mountain West:

Powdery Mildew

• What it looks like: White or grayish powdery coating on leaves, stems, and sometimes flower buds. Leaves may curl, yellow, and eventually die.
• What causes it: Various fungi thrive in warm days and cool nights. While we have low humidity, the temperature swings can still create favorable conditions.
• How to fix/prevent it: Improve air circulation by spacing plants adequately and pruning if needed. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help. A milk spray (1 part milk to 9 parts water) is also 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 can explode during warm spells.
• How to fix/prevent it: A strong spray of water can knock them off. Encourage natural predators like ladybugs and lacewings. Insecticidal soap is effective for heavy infestations. Avoid over-fertilizing with nitrogen, as it attracts aphids.

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, sheltered conditions. They can quickly build up large populations.
• How to fix/prevent it: Use yellow sticky traps to catch adult whiteflies. Spray plants with insecticidal soap or neem oil, paying attention to the undersides of leaves. Encourage natural predators like lacewings and parasitic wasps.

Mountain West Specific Challenges: Our intense sun can sometimes scorch calendula leaves if they're not adequately watered, so be mindful of that. The alkaline soil can also affect nutrient uptake, so consider amending your soil with compost to improve its overall health.

Companion planting can greatly benefit your calendula and other garden plants in the Mountain West.

Calendula is a great companion for tomatoes and peppers. It attracts beneficial insects like ladybugs and lacewings, which prey on aphids and other pests that commonly attack these crops. Plus, calendula's strong scent can help deter tomato hornworms.

Green beans also benefit from being planted near calendula. Calendula helps repel bean beetles, reducing the need for pesticides. Avoid planting calendula near plants in the cabbage family, as it can attract cabbage moths.