Chrysanthemum in Zone 7A — Mountain West

Chrysanthemums are a fantastic addition to any high-altitude garden, bringing vibrant fall color just when many other plants are fading. Their daisy-like blooms add a cheerful touch to bouquets, and their relatively compact size makes them easy to fit into smaller gardens or containers. Plus, the cool nights we experience even in summer here in the Mountain West help intensify their colors.

Growing Chrysanthemums in our Zone 7A Mountain climate does come with its challenges, like intense sun and a short growing season of around 173 days. But by starting smart and paying attention to watering, you can easily enjoy these beauties in your garden.

Starting Chrysanthemum from seed indoors isn't always necessary, as you can often find healthy starter plants at local nurseries in spring or even established, blooming mums in fall. However, if you're looking for specific varieties or want a head start, indoor sowing is an option.

Sow seeds indoors from mid-February through early March, about eight weeks before you plan to transplant. Use seed trays with a well-draining seed starting mix, and provide warmth (around 70°F) and plenty of light. Bottom watering is a great way to keep the soil consistently moist without disturbing the delicate seedlings. Remember, our late spring means it's better to be patient than rush things.

Transplant your Chrysanthemum seedlings outdoors from mid-April through mid-May, 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. This helps them adjust to the intense sun and cooler nights we often experience.

Space your plants 12-18 inches apart to allow for good air circulation. Keep an eye on the weather forecast, as late-season frosts can still occur. Be ready to cover your plants if temperatures dip unexpectedly.

Consistent watering is key to thriving Chrysanthemums, especially given our dry climate and low humidity. Aim for regular watering at the base of the plant, avoiding wetting the foliage as much as possible. This helps prevent fungal diseases that can sometimes pop up.

During the warmer months, from late spring through summer, check the soil moisture regularly. Stick your finger about two inches deep into the soil; if it feels dry, it's time to water. Typically, this means providing about an inch of water per week, but adjust based on rainfall and temperatures. In the Mountain West, we tend to dry out quickly, so be diligent!

Overwatering can lead to root rot, indicated by yellowing leaves and a general decline in plant health. Underwatering, on the other hand, will cause wilting and stunted growth. A layer of mulch around the base of the plant will help retain moisture and keep the soil cool, which is especially helpful in our intense sun.

Pruning Chrysanthemums is simple and helps encourage bushier growth and more abundant blooms. From the time your plants are young until around July 4th, pinch off the growing tips of the stems every 2-3 weeks. This encourages the plant to branch out and produce more flowering stems.

When you pinch, remove just the top set of leaves. After July 4th, stop pinching. This allows the flower buds to develop for fall blooming. As the season winds down and the first frost approaches in early October, you can leave the dead foliage on the plant as winter protection, or cut it back to a few inches above the ground.

You can expect your first Chrysanthemum blooms from late June through mid-August, depending on the variety and when you transplanted. These are fall-blooming flowers. The blooms last for weeks in the garden, providing a long season of color.

Cut the flowers for bouquets when they are fully open, selecting stems with strong, straight growth. Use sharp, clean pruners to avoid damaging the plant. Cutting the blooms encourages the plant to produce more flowers, so harvest frequently. As the first frost approaches, you can cut any remaining blooms to enjoy indoors, extending your harvest season.

Chrysanthemums can sometimes be susceptible to a few common pests and diseases, especially in our challenging climate. Here's what to watch out for:

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).

Spider Mites

• What it looks like: Fine stippling on leaves (tiny white dots). Fine webbing on leaf undersides and between stems. Leaves turn bronze or yellow.
• What causes it: Tiny arachnids that thrive in hot, dry conditions. Populations explode in drought stress.
• How to fix/prevent it: Strong water spray (daily for a week) is the best treatment. Increase humidity around plants. Neem oil or insecticidal soap. Release predatory mites (Phytoseiulus persimilis). Avoid broad-spectrum pesticides that kill predators.

Leaf Miners

• What it looks like: Tan, squiggly lines or blotches inside the leaves.
• What causes it: The larvae of small flies that tunnel between the leaf surfaces to feed.
• How to fix/prevent it: Remove and destroy affected leaves. Cover plants with row covers to prevent the flies from laying eggs. Insecticidal soap or neem oil can help control infestations.

Rust

• What it looks like: Rusty orange, yellow, or brown pustules on leaves and stems, mostly on undersides. Leaves yellow and drop prematurely.
• What causes it: Various rust fungi that spread via wind-borne spores. Favored by warm, humid conditions with moisture on leaves.
• How to fix/prevent it: Remove affected leaves. Avoid overhead watering. Improve air circulation. Apply sulfur or copper fungicide. Don't work among wet plants. Rotate crops.

Mountain West Specific Challenges: The intense UV radiation and dry conditions in the Mountain West can stress plants, making them more susceptible to pests and diseases. Consistent watering, proper spacing for air circulation, and vigilant monitoring are key to keeping your Chrysanthemums healthy. Our alkaline soil can sometimes be an issue, so amending with compost can help improve nutrient availability.

Chrysanthemums make great companions for a variety of plants in the Mountain West garden. They pair well with tomatoes and peppers, as they can help repel certain pests that bother those vegetables. The strong scent of Chrysanthemums can deter aphids and other insects.

Lettuce also benefits from being planted near Chrysanthemums. The taller plants can provide some shade during our intense summer sun, which can help prevent lettuce from bolting prematurely. Avoid planting Chrysanthemums near because .