Chrysanthemum in Zone 6A — Pacific Northwest

Chrysanthemums, with their vibrant fall blooms, are a welcome sight in any Pacific Northwest garden. Their late-season color extends the gardening season, providing beauty just as other plants are fading. Cool nights here actually enhance their flower color and longevity, and they make fantastic cut flowers for bringing the outdoors in.

While our mild summers are generally kind to Chrysanthemums, you'll want to pay attention to watering during our dry summer months. With a 148-day growing season, careful timing will ensure your Chrysanthemums thrive and provide a burst of color when you need it most.

Starting Chrysanthemums from seed indoors in the PNW isn't as common as buying starts, but it’s certainly doable if you're keen on specific varieties. Starting indoors gives you a head start, especially with our relatively short growing season.

If you choose to start seeds, aim for early to late March, about 8 weeks before you intend to transplant them outdoors. Use seed trays with a good seed-starting mix, provide warmth (a heat mat helps), and ensure they get plenty of light – a grow light is almost essential during our often overcast spring days. Don't forget to bottom water your seedlings to encourage strong root growth and prevent damping off.

Transplanting Chrysanthemums outdoors in the Pacific Northwest is best done from early May through early June, once the risk of frost has passed. You can often find potted mums at nurseries in the fall for immediate color or starts in the spring to get a jump on the season.

Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. Choose a sunny spot with well-draining soil, and space plants 12-18 inches apart. Keep an eye on the weather forecast – a late cold snap can still happen, so be prepared to cover your young plants if necessary.

Chrysanthemums need consistent moisture, especially during bud formation, but they are not drought-tolerant. Getting the watering right is crucial in our Pacific Northwest climate, where we experience wet springs and dry summer months.

During the spring, when rainfall is more frequent, you may only need to supplement with watering if the soil feels dry to the touch about 2 inches down (the "finger test"). In the drier summer months, plan to water deeply about 1-2 inches per week, depending on rainfall. Always water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our humid climate.

Signs of underwatering include wilting leaves and dry soil, while yellowing leaves and soggy soil indicate overwatering. A layer of mulch around the base of your plants helps retain moisture in our dry summers and keeps the soil temperature consistent.

Pinching your Chrysanthemums is key to getting a bushy plant with lots of blooms. It's a simple technique that makes a big difference.

Pinch off the growing tips of the stems every 2-3 weeks through July 4th. This encourages the plant to branch out and produce more flower buds. After July 4th, stop pinching so the flower buds can develop for fall blooming. At the end of the season, after the first frost around early October, you can cut back the plant to a few inches above the ground.

You can expect your first Chrysanthemum blooms from mid July through early September here in the Pacific Northwest, depending on the variety and when you planted them. They are fall-blooming plants.

The flowers will last for weeks in the garden, providing a long season of color. Cut the flowers for bouquets when they are fully open, snipping the stems at an angle. Removing spent flowers encourages the plant to produce more blooms. As the first frost approaches in early October, harvest any remaining blooms to enjoy indoors.

Chrysanthemums can face a few common problems in the Pacific Northwest. Here's how to deal with them:

Aphids

• What it looks like: Clusters of tiny soft-bodied insects (green, black, or white) on stems and leaf undersides. Sticky honeydew residue and curled or distorted new growth.
• What causes it: Rapid-reproducing sap-sucking insects. Populations explode in warm weather, and ant colonies may farm them for honeydew.
• How to fix/prevent it: A strong spray of water will knock them off. Encourage ladybugs and lacewings to visit your garden. Use insecticidal soap for heavy infestations or neem oil for systemic control. Avoid excess nitrogen fertilizer.

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 during periods of drought stress, which can happen in our dry summer months.
• How to fix/prevent it: Strong water spray (daily for a week) is the best treatment. Increase humidity around plants. Use neem oil or insecticidal soap. Release predatory mites. Avoid broad-spectrum pesticides.

Leaf Miners

• What it looks like: Tunnels or trails inside the leaves. The leaves may appear distorted or blotchy.
• What causes it: Larvae of small flies or moths that burrow between the leaf surfaces to feed.
• How to fix/prevent it: Remove and destroy infested leaves. Cover plants with row covers to prevent adult insects from laying eggs. Use neem oil to control larvae.

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 around your plants. Apply sulfur or copper fungicide. Don't work among wet plants, and rotate crops.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall can create conditions that favor spider mites and rust. Be vigilant about watering at the base of the plant and monitoring for early signs of infestation or disease.

Chrysanthemums benefit from companion planting in the Pacific Northwest garden. Tomatoes and peppers make good companions because they attract beneficial insects that can help control pests like aphids. Lettuce also works well, as it provides ground cover that helps retain soil moisture, which is particularly helpful during our dry summer months. Avoid planting Chrysanthemums near plants that are susceptible to the same diseases, as this can increase the risk of spreading problems.