Chrysanthemum in Zone 3A — Great Plains

Chrysanthemums bring late-season color to our Plains gardens, just when we need it most. Their cheerful blooms brighten up the landscape as other flowers fade, and they make stunning cut flower arrangements to enjoy indoors. Plus, there’s real satisfaction in extending the growing season with these hardy beauties.

Our extreme weather can be tough on plants, but with careful timing, Chrysanthemums are very manageable. You have about a 108-day growing season to work with. By starting indoors or buying transplants, you can get a jumpstart and enjoy a beautiful display of fall blooms.

Starting Chrysanthemums indoors in our Zone 3A climate can give you a head start, but it's not always essential. If you want earlier or specific varieties, it's a good option. Otherwise, buying transplants from a local nursery can be just as effective.

If you choose to start seeds indoors, aim for late March through mid April, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and provide warmth and plenty of light, either from a sunny window or grow lights. Water from the bottom to avoid damping off, especially with our variable spring weather.

Transplanting Chrysanthemums outdoors should happen late May through mid June, after the risk of frost has passed. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space your plants 12-18 inches apart to allow for good air circulation and healthy growth. Keep an eye on the forecast for any late-season cold snaps. Buying potted mums in fall or starts in spring from a local nursery is a common practice for Plains gardeners, and often the easiest way to go.

Chrysanthemums need consistent moisture, but they don’t like to be waterlogged. In our hot, and sometimes dry, Plains climate, watering correctly is key. A general rule is to water deeply about once a week, providing about 1 inch of water. But adjust based on rainfall and soil moisture.

The "finger test" is your best guide: stick your finger about 2 inches deep into the soil. If it feels dry, it’s time to water. Always water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our low-to-moderate humidity. During bud formation, consistent moisture is especially crucial.

Signs of underwatering include wilting leaves and dry, crispy edges. Overwatering can lead to yellowing leaves and root rot. A layer of mulch around your plants helps retain moisture and regulate soil temperature, which is especially helpful during our extreme temperature swings.

Pruning Chrysanthemums is all about encouraging bushier plants with more blooms. Pinch the growing tips of your plants every 2-3 weeks through July 4th. This encourages side shoots to develop, resulting in more flowering stems.

Pinching means snipping off the very top set of leaves on each stem. After July 4th, stop pinching. This allows the flower buds to develop for your fall display. As the first frost approaches in early September, you can cut back the plants to a few inches above the ground after they finish blooming.

You can expect your first Chrysanthemum blooms in early August through mid September, depending on the variety and when you transplanted. These are fall-blooming plants, so be patient. The flowers last for weeks in the garden and make excellent cut flowers.

Harvest when the flowers are fully open for the longest vase life. Cut the stems at an angle, and remove any leaves that will be below the water line in your vase. Chrysanthemums will continue to produce blooms throughout the fall if you deadhead spent flowers regularly.

As the first frost approaches in early September, harvest any remaining blooms to enjoy indoors. You can also try covering your plants with a frost blanket to extend the blooming season a bit longer.

Chrysanthemums can face a few challenges in the Plains, but with vigilance, you can keep them healthy. Here are four common problems 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, winding trails or blotches inside the leaves. Leaves may appear distorted or turn brown.
• What causes it: The larvae of small flies that tunnel between the upper and lower leaf surfaces, feeding on the leaf tissue.
• How to fix/prevent it: Remove and destroy affected leaves. Cover plants with row covers to prevent adult 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.

Great Plains Specific Challenges: The hot heat and variable rainfall of the Great Plains can stress Chrysanthemums, making them more susceptible to pests and diseases. Monitor your plants regularly, provide consistent moisture, and ensure good air circulation to keep them healthy. Our wind can also spread fungal spores, so be extra careful to remove any infected foliage promptly.

Chrysanthemums benefit from companion plants that offer protection or attract beneficial insects. Tomatoes and peppers make good companions because they provide some shade and wind protection, which is essential in our windy Plains environment. Plus, they don’t compete for the same nutrients.

Lettuce is another good companion, as it can help suppress weeds and keep the soil cool and moist. Avoid planting Chrysanthemums near plants that are prone to fungal diseases, as this can increase the risk of rust and other problems.