Chrysanthemum in Zone 6B — Pacific Northwest

Chrysanthemums are a fantastic addition to any Pacific Northwest garden. Their vibrant blooms bring welcome color as the days shorten, extending the beauty of your garden well into fall. Plus, their long-lasting flowers make excellent cut flowers, brightening up your home as the weather turns.

While we might not have the long, scorching summers of other regions, our mild summers and cool nights actually enhance the color and vibrancy of Chrysanthemums. With a little attention to timing within our 162-day growing season, you can successfully grow these beauties.

Starting Chrysanthemums indoors is an option, but honestly, most of us in the PNW find it easier to buy starts from a local nursery. However, if you're keen on starting from seed, aim for late February through mid March, about eight weeks before you plan to transplant.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist by bottom watering to prevent damping off, and provide warmth and plenty of light – a grow light is almost essential here during our often overcast spring days. Remember, our springs can be slow to warm up, so patience is key.

Transplanting your Chrysanthemums outdoors can happen from early to late May, once the risk of frost has passed. Before you commit, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Plant them 12-18 inches apart in a sunny spot with well-draining soil. Keep an eye on the weather; even in May, we can get unexpected cool snaps, so be ready to cover your young plants if needed. Many gardeners simply purchase potted mums in the fall for instant color, or starts from local nurseries in spring.

Consistent watering is key for Chrysanthemums, especially during our dry summer months. While we don't often see extreme heat, consistent moisture is still vital for healthy growth and abundant blooms.

During the spring and early summer, when rainfall is more frequent, check the soil moisture regularly. Use the "finger test" – if the top two inches of soil feel dry, it's time to water. Aim for about an inch of water per week, watering deeply at the base of the plant to avoid wetting the foliage. As the weather warms up in July and August, you may need to increase watering frequency, but always allow the soil surface to dry out slightly between waterings.

Signs of underwatering include wilting leaves and dry, brittle stems. Overwatering can lead to yellowing leaves and root rot. Mulching around your plants with compost or bark chips helps retain moisture and suppress weeds, especially beneficial in our typically dry summers.

Pruning Chrysanthemums is crucial for encouraging a bushy growth habit and maximizing flower production. The key is pinching – removing the growing tips of the stems.

Start pinching about two weeks after transplanting and continue every 2-3 weeks until around July 4th. This encourages the plant to branch out, resulting in more stems and, consequently, more flowers. After July 4th, stop pinching to allow the flower buds to develop. As the first frost approaches around early October, remove any dead or dying foliage to prevent disease.

In the Pacific Northwest, you can expect your first Chrysanthemum blooms from early July through late August, depending on the variety and when you transplanted.

The flowers are ready to harvest when they are fully open and the petals are firm. Cut the stems at an angle, leaving several inches of stem on the plant to encourage further blooming. Regular deadheading (removing spent flowers) will also promote continuous flowering throughout the season.

As the first frost approaches in early October, you can cut the remaining blooms to enjoy indoors. Chrysanthemums are fall-blooming, so enjoy their color as long as the weather allows!

Even in the relatively pest-free Pacific Northwest, Chrysanthemums can encounter a few problems. Here's how to handle them:

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: Winding, whitish or yellowish trails inside the leaves. Leaves may become distorted or blotched.
• What causes it: Larvae of small flies or sawflies that tunnel between the leaf surfaces.
• How to fix/prevent it: Remove and destroy affected leaves. Floating row covers can prevent adult flies from laying eggs. Neem oil can deter egg-laying. Systemic insecticides are a last resort.

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.

Pacific Northwest Specific Challenges: Our mild, dry summers generally reduce the risk of fungal diseases compared to more humid regions. However, consistent monitoring is still crucial. Slugs, while not specific to Chrysanthemums, are a constant nuisance in our wet springs. Use slug bait or traps to protect young plants.

Chrysanthemums benefit from companion planting, especially in the Pacific Northwest. Plant them near tomatoes and peppers; these plants help deter pests that might bother your mums. Lettuce also makes a good companion, as it provides ground cover that helps retain moisture in the soil, which is crucial during our dry summer months. Avoid planting near anything that might shade your Chrysanthemums, as they need full sun to thrive and produce abundant blooms.