Chrysanthemum in Zone 7B — Pacific Northwest

Chrysanthemums bring a burst of color to your garden in late summer and fall, just when many other flowers are fading. Their vibrant blooms and long vase life make them a favorite for bouquets, adding cheer as the days get shorter here in the PNW. The cool nights we often have actually deepen their colors, giving you even more beautiful blooms.

While our wet springs and mild summers can present some challenges, particularly with fungal diseases, Chrysanthemums are well-suited to our 193-day growing season. With a little planning, you can enjoy a stunning display of these beauties in your garden.

Starting Chrysanthemum from seed indoors is possible, but it's not the most common approach for us here in the Pacific Northwest. Most gardeners either buy established plants in the fall or starts in the spring. If you're set on starting from seed, begin in mid-February through early March, about 8 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and provide consistent warmth (around 70°F) and bright light, either from a sunny window or grow lights. Bottom watering can help prevent damping-off disease, which can be a problem during our overcast spring days. Keep the soil consistently moist, but not soggy.

Transplant your Chrysanthemum starts outdoors from mid-April through mid-May, once the danger 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 cooler temperatures and stronger sunlight.

Choose a sunny spot with well-draining soil and space the plants 12-18 inches apart. Keep an eye on the weather forecast, as late frosts can still occur during this time. Be prepared to cover your transplants if a frost is predicted. If you buy established plants, you can plant them directly into the garden at this time.

Chrysanthemums need consistent moisture, especially during bud formation, but they don't like to sit in soggy soil. Here in the Pacific Northwest, our dry-summer conditions mean you'll need to pay attention to watering, particularly from late spring through early fall. Aim to keep the soil evenly moist.

A good way to check is the "finger test": stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. During our drier summer months, you might need to water deeply about 1 inch per week. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases.

Signs of underwatering include wilting leaves and dry soil. Overwatering can lead to yellowing leaves and root rot. Applying a layer of mulch around your plants can help retain moisture and keep the soil cool during our mild summers.

Pinching your Chrysanthemums is key to getting those full, bushy plants with tons of blooms. Start pinching the growing tips every 2-3 weeks, beginning when the plants are about 6 inches tall.

Pinch off the top set of leaves on each stem, which encourages the plant to branch out. Stop pinching around July 4th. This allows the plants to focus on developing flower buds for a fall display. After the first frost, you can cut back the plants to a few inches above the ground.

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

Cut the flowers for bouquets when they are fully open, choosing stems with strong, straight stalks. Use clean, sharp pruners to make the cut, and cut the stem at an angle just above a leaf node. This encourages the plant to produce more flowers.

As the first frost approaches in late October, you can cut all the remaining blooms to enjoy indoors. After the frost, cut back the plants to just above ground level.

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: Tan, winding trails or blotches inside the leaves.
• What causes it: Larvae of small flies that tunnel between the leaf surfaces.
• How to fix/prevent it: Remove and destroy infested leaves. Cover plants with row covers to prevent adult flies from laying eggs. 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.

Pacific Northwest Specific Challenges: Our mild summers and dry-summer conditions can actually help minimize some problems, like spider mites, compared to hotter, drier climates. However, our wet springs can increase the risk of fungal diseases like rust. Good air circulation and avoiding overhead watering are key to prevention. Slugs can also be a nuisance, especially on young plants, so use your preferred slug control methods.

Chrysanthemums make great companions for several plants in your Pacific Northwest garden. Tomatoes and peppers benefit from having Chrysanthemums nearby, as the scent of Chrysanthemums can help repel aphids and other pests that commonly attack these warm-season crops.

Lettuce also appreciates the shade provided by Chrysanthemums during our mild summer months, which can help prevent bolting. Avoid planting Chrysanthemums near plants in the cabbage family, like broccoli or kale, as they can attract similar pests, such as cabbage worms.