Chrysanthemum in Zone 7A — Pacific Northwest

Chrysanthemums bring a burst of color to your garden in the late summer and early fall, just when many other flowers are fading. Their vibrant blooms make excellent cut flowers, and the cool nights of the Pacific Northwest actually enhance their colors. Plus, they're relatively easy to grow here.

Our mild summers and long, cool autumns give Chrysanthemums plenty of time to mature, but the wet springs can be a bit of a hurdle. With a growing season around 183 days, you have plenty of time to get them established, as long as you manage moisture early on.

Starting Chrysanthemums from seed indoors isn't always necessary, especially since you can often find healthy starts at local nurseries in spring or potted mums in the fall. However, if you want specific varieties or a head start, starting indoors is an option.

If you choose to start seeds indoors, aim for mid-February through early March, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix, provide warmth (a heat mat helps), and ensure they get plenty of light, especially with our overcast spring days. Bottom watering is ideal to prevent damping off.

Transplant your Chrysanthemum seedlings outdoors from mid-April through mid-May, once the risk of frost has passed. Before planting, harden them off 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 to allow for good air circulation. Even in late spring, our soils can still be cool and wet, so make sure the planting location has well-draining soil. Many gardeners buy potted mums in the fall, or starts in spring.

Chrysanthemums need consistent moisture, but overwatering can be a problem, especially during our wet springs. During the drier summer months, you'll likely need to water them more regularly, but always check the soil first.

Stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim to give them about 1 inch of water per week, either from rainfall or supplemental watering. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our climate.

In the spring, you may only need to water once a week, if at all, depending on rainfall. During the drier summer months, increase watering to two or three times a week as needed. Drooping leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. Mulching around the base of the plants with compost or shredded bark helps retain moisture and suppress weeds.

Pruning Chrysanthemums is key to getting bushier plants with more blooms. The main technique is pinching, where you remove the growing tips of the stems.

Start pinching the tips every 2-3 weeks, beginning when the plants are about 6 inches tall and continue until around July 4th. This encourages the plant to branch out and produce more flower buds. After July 4th, stop pinching to allow the flower buds to develop. At the end of the season, after the first frost, cut back the plants to a few inches above the ground.

You can expect your first Chrysanthemum blooms to appear in late June through mid-August, about 70 days after transplanting. Chrysanthemums are fall-blooming, so you'll get a beautiful show just as other flowers are finishing up.

The flowers last for weeks in the garden, providing long-lasting color. Cut the flowers for bouquets when they are fully open. To encourage continued production, deadhead spent flowers regularly.

As the first frost approaches in mid-October, you can cut the remaining flowers to enjoy indoors. After a hard frost, cut the plants back to just a few inches above the soil line. Some gardeners treat them as annuals, while others leave them in the ground, hoping they'll return the following spring.

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

Aphids *What it looks like:* Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also see a sticky honeydew residue or curled, distorted new growth. *What causes it:* Rapidly reproducing sap-sucking insects that thrive in warm weather. Ant colonies may farm them. *How to fix/prevent it:* A strong spray of water can knock them off. Encourage ladybugs and lacewings. Use insecticidal soap for heavy infestations. Neem oil also works. 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 drought stress. *How to fix/prevent it:* Strong water spray daily for a week is a good treatment. Increase humidity around plants. Use neem oil or insecticidal soap. Release predatory mites. Avoid broad-spectrum pesticides.

Leaf Miners *What it looks like:* Squiggly, pale trails or blotches within the leaves. *What causes it:* Larvae of small flies that tunnel between the leaf surfaces. *How to fix/prevent it:* Remove and destroy affected leaves. Cover plants with floating row covers to prevent adult flies from laying eggs. Apply neem oil to deter egg-laying.

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 generally don't create ideal conditions for spider mites, but dry spells can cause outbreaks. The biggest concern is rust, which can be exacerbated by our wet springs and occasional humid conditions. Be vigilant about removing affected foliage and providing good air circulation. Late blight isn't a direct threat to Chrysanthemums, but the conditions that favor blight can also encourage other fungal diseases. Slugs can be a nuisance, especially for young plants, so use your preferred slug control methods.

Chrysanthemums make good companions for several vegetables in the Pacific Northwest garden. Plant them near tomatoes and peppers; Chrysanthemums can help repel certain pests that bother these warm-season crops. Lettuce also benefits from being planted near Chrysanthemums, as they can provide some shade during the warmer parts of the day, preventing bolting.

Avoid planting Chrysanthemums near plants that are susceptible to the same fungal diseases, as this can increase the risk of spreading infection.