Calendula in Zone 5A — Mountain West

Calendula is a fantastic flower to grow in our Mountain West gardens. The petals add a pop of color to salads and baked goods, plus they have medicinal properties. But honestly, the sheer joy of having vibrant blooms in your garden, even with our short season and intense sun, makes it worthwhile.

Our high altitude and short growing season (around 138 days) can be challenging, but Calendula is surprisingly adaptable. With the right timing and a little attention, you can enjoy a long season of blooms.

Starting Calendula indoors isn't strictly necessary, but it can give you a head start, especially if you're aiming for earlier blooms. If you want to go this route, sow seeds indoors from early to late March, about 6 weeks before you plan to transplant them outside.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist (bottom watering is a great trick to prevent damping off) and provide a warm environment with plenty of light – a sunny windowsill or grow lights will do the trick. Remember, our spring weather can be unpredictable, so indoor starting offers some protection.

Transplant your Calendula seedlings outdoors from late April through early June, after the danger of hard frost has passed. Before transplanting, harden off your seedlings 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 your plants 8-12 inches apart in a sunny spot with well-drained soil. Keep an eye on the weather forecast; a late frost can still happen, so be ready to cover your seedlings if needed.

Direct sowing Calendula is easy and often successful in our climate. Sow seeds directly into the garden from late April through late July. This gives you flexibility for succession planting and ensures blooms throughout the season.

Choose a spot with full sun to partial shade. Prepare the soil by loosening it and removing any weeds. Sow seeds about ½ inch deep and 8-12 inches apart. Keep the soil consistently moist until the seedlings emerge, which usually takes about a week.

Calendula needs moderate watering, especially during its active growing and blooming periods. While it can tolerate some drought, consistent moisture helps it thrive, particularly with our dry air. However, avoid overwatering, which can lead to problems.

During the spring and fall, when temperatures are cooler, water deeply once or twice a week, providing about 1 inch of water. In the heat of summer, increase watering to two or three times a week, ensuring the soil doesn't completely dry out between waterings. Use the "finger test" – if the top 2 inches of soil feel dry, it's time to water.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases, although our low humidity usually keeps that in check. Signs of underwatering include wilting and yellowing leaves. Overwatering can lead to root rot, indicated by soggy soil and stunted growth. Mulching around the base of the plants with straw or wood chips helps retain moisture and regulate soil temperature.

Deadheading is essential for keeping your Calendula plants blooming all season long. Regularly remove spent flowers to encourage the plant to produce more blooms. Simply pinch or cut off the flower heads just below the base of the flower.

Throughout the growing season, focus on removing faded or dead flowers. As the first frost approaches in late September, you can let some of the last flowers mature and go to seed if you want them to self-sow for next year.

You can expect your first Calendula harvest from early June through early October, depending on when you planted. The flowers are ready to harvest when they are fully open. Pick them in the morning after the dew has dried for the best flavor and medicinal properties.

To harvest, simply snip the flower heads off the stem. Regular harvesting encourages the plant to produce more flowers. As the end of the season nears and frost threatens, harvest all remaining open flowers and buds. You can dry the petals for later use.

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

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 that thrive in warm days, cool nights, and moderate humidity. Dry leaf surfaces actually favor it.
• How to fix/prevent it: Improve air circulation by spacing plants properly and pruning out crowded growth. Remove affected leaves promptly. Neem oil or potassium bicarbonate sprays can help control the spread. 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 may be present. New growth may be curled or distorted.
• What causes it: These sap-sucking insects reproduce rapidly, especially in warm weather. Ant colonies may farm them for the honeydew they produce.
• How to fix/prevent it: A strong spray of water can knock aphids off plants. Encourage beneficial insects like ladybugs and lacewings, which are natural predators. Insecticidal soap is effective for heavy infestations. Neem oil also works well. Avoid over-fertilizing with nitrogen, as this attracts aphids.

Whiteflies

• What it looks like: Tiny, white, moth-like insects that fly up when disturbed. Yellowing or stippled leaves. Sticky honeydew residue.
• What causes it: Warm temperatures and high humidity can cause whitefly populations to explode. They suck plant sap, weakening the plant.
• How to fix/prevent it: Hang yellow sticky traps to catch adult whiteflies. Spray plants with insecticidal soap or neem oil, paying close attention to the undersides of leaves. Encourage beneficial insects like lacewings and parasitic wasps.

Mountain West Specific Challenges: Our intense sun can sometimes stress Calendula, so providing some afternoon shade can be helpful. While our low humidity generally reduces fungal issues, powdery mildew can still occur with those cool nights. The dry conditions mean consistent watering is key, but be careful not to overwater in our alkaline soil.

Calendula makes a great companion plant in our Mountain West gardens. Plant it near:

• Tomatoes: Calendula attracts beneficial insects like ladybugs and lacewings, which prey on tomato pests like aphids.
• Peppers: Similar to tomatoes, Calendula helps protect peppers from common pests.
• Green Beans: Calendula can help deter bean beetles and other pests that attack beans.

Avoid planting Calendula near cabbage family plants (broccoli, cabbage, kale), as they can compete for nutrients.