Chrysanthemum in Zone 8A — Northern California

Chrysanthemums are a fantastic addition to any Northern California garden, bringing vibrant color and classic beauty to your fall landscape. Their long-lasting blooms make stunning cut flowers, and they're relatively easy to grow, fitting right into our Mediterranean climate.

While we face challenges like summer heat and periodic drought, the long growing season in our zone 8A allows you ample time to establish healthy chrysanthemums for a spectacular autumn display. Plus, with a growing season that stretches for about 255 days, you can easily work around any unexpected temperature swings.

Starting chrysanthemums indoors is optional but can give you a jump start, especially if you want specific varieties or are aiming for earlier blooms. Begin in early to late January, roughly eight weeks before you plan to transplant them outdoors.

Use seed trays with a good seed-starting mix, providing warmth (a heat mat is helpful) and plenty of light (grow lights are ideal). Water from the bottom to avoid damping off, and keep the soil consistently moist. Our early spring warmth in NorCal can be deceiving, so starting indoors offers more control.

Transplant your chrysanthemum seedlings outdoors in early March through early April, once the danger of frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space them 12-18 inches apart in a sunny location with well-draining soil. While our early spring weather is generally mild, be mindful of any late cold snaps that can occur. You can also purchase established starts from local nurseries during the spring, or potted mums in the fall.

Chrysanthemums need consistent moisture, especially during bud formation. In our Northern California climate, with its dry summers, regular watering is crucial.

During the warmer months, check the soil moisture by sticking your finger about two inches deep. If it feels dry, it's time to water. Aim for about 1 inch of water per week, delivered at the base of the plant to avoid wetting the foliage, which can lead to fungal diseases in our sometimes foggy microclimates. Signs of underwatering include wilting leaves and dry, brittle buds. Overwatering can cause root rot, indicated by yellowing leaves and a mushy base. Mulching around your plants helps retain moisture and regulate soil temperature, especially important with our water restrictions.

Pinching your chrysanthemums is key to encouraging bushier plants with more blooms. From spring until around July 4th, pinch off the growing tips every two to three weeks.

This directs the plant's energy into producing more side shoots, resulting in a fuller, more floriferous plant. After July 4th, stop pinching to allow the flower buds to develop. As the first frost approaches around mid- November, you can cut back the foliage to a few inches above the ground to prepare the plant for winter dormancy.

Expect your first chrysanthemum blooms from mid May through early July, depending on the variety and when you started them. 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 continued production. Regular harvesting encourages more blooms, extending the flowering season. As the first frost nears in mid- November, harvest any remaining blooms to enjoy indoors.

Chrysanthemums can sometimes encounter a few common problems:

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 inside the leaves. Leaves may appear distorted or blistered.
• What causes it: Larvae of small flies that tunnel between the leaf surfaces.
• How to fix/prevent it: Remove and destroy affected leaves. Use floating row covers to prevent adult flies from laying eggs. Neem oil can deter egg-laying. Spinosad is effective against larvae inside the leaves.

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.

Northern California Specific Challenges: Our moderate-to-hot, dry summers and low humidity can stress chrysanthemums, making them more susceptible to spider mites and drought stress. Consistent watering and good air circulation are key to keeping your plants healthy. Watch out for leaf miners, especially during the spring.

Chrysanthemums benefit from companion planting. Tomatoes and peppers make good companions because they deter certain pests, helping protect the chrysanthemums.

Lettuce is another great companion, providing ground cover that helps retain moisture in our dry climate, benefiting the chrysanthemums. Avoid planting chrysanthemums near plants that require very different watering schedules, as consistent moisture is key for healthy chrysanthemum growth.