Chrysanthemum in Zone 8A — Pacific Northwest

Chrysanthemums are a fantastic choice for adding late-season color to your Pacific Northwest garden. Their vibrant blooms brighten up the landscape just as other flowers are fading, and their cool-season tolerance means they'll last well into our characteristically long, mild fall. Plus, cut Chrysanthemums last a long time in bouquets.

While we don't have the intense heat that some plants crave, you can definitely grow Chrysanthemums successfully here. Our 203-day growing season gives you plenty of time to get them established and blooming before our first frost. Timing is key, and with a little planning, you’ll have beautiful blooms.

Starting Chrysanthemums indoors is an option, but most of us here in the PNW typically buy starts in spring or potted mums in fall. If you want to try starting from seed, begin in early to late February, about eight weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, and keep them warm and consistently moist. Bottom watering is a great way to prevent damping off, which can be a problem during our overcast spring days. Provide supplemental light, as our spring sunshine can be a bit weak.

Transplant your Chrysanthemums outdoors from early April through early May, once the danger of hard 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 cooler temperatures and stronger sunlight.

Space them 12-18 inches apart in a sunny spot with well-drained soil. Even though we have mild summers, a sheltered location can protect them from any unexpected temperature swings. You might need to protect young transplants from slugs, as those pests are always lurking in our wet springs.

Chrysanthemums need consistent moisture, but overwatering can lead to problems, especially with our dry-summer humidity. Aim to keep the soil evenly moist, but not soggy. During our wet springs, you may not need to water them much at all.

During the dry summer months, check the soil moisture regularly. Stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Aim for about an inch of water per week, watering at the base of the plant to avoid wetting the foliage.

Overhead watering can encourage fungal diseases in our climate, even with our dry-summer conditions. Signs of underwatering include wilting leaves and dry, brittle stems. Overwatering can lead to yellowing leaves and root rot. Applying a layer of mulch around your plants helps retain moisture and suppress weeds.

Pinching your Chrysanthemums is essential for encouraging bushy growth and abundant blooms. Begin pinching the growing tips every 2-3 weeks, starting when the plants are about 6 inches tall. This encourages side shoots to develop, creating a fuller plant.

Stop pinching around July 4th. This allows the plants to focus their energy on bud formation for fall flowering. As the first frost approaches in late October, you can cut back the plants to a few inches above the ground.

You can expect your first Chrysanthemum blooms from mid-June through early August, depending on the variety and when you transplanted. Fall-blooming mums will reward you with color as the season wanes. The flowers last for weeks in the garden.

Cut the flowers for bouquets when they are fully open. Use clean, sharp scissors or pruners to avoid damaging the plant. Cutting the flowers encourages the plant to produce more blooms. As the first frost approaches in late October, harvest any remaining blooms to enjoy indoors.

Here are some common problems you might encounter with Chrysanthemums in the Pacific Northwest:

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:
• What causes it:
• How to fix/prevent it:

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 heat and dry-summer rainfall mean that fungal diseases like rust can still be a problem, especially if air circulation is poor. Keep an eye out for these issues and take preventative measures to ensure healthy plants. Slugs are always a concern, especially with young plants.

Chrysanthemums benefit from companion planting. Tomatoes and peppers make good companions because they are heavy feeders and don't compete for the same nutrients. Lettuce can also be a good companion, as it provides ground cover and helps retain moisture in the soil. Avoid planting Chrysanthemums near plants that are susceptible to the same pests or diseases, as this can increase the risk of problems.