Chrysanthemum in Zone 7A — Northern California

Chrysanthemums bring vibrant color and classic beauty to your Northern California garden, especially as other blooms fade. Their long-lasting flowers make them perfect for bouquets and adding cheer to your outdoor spaces. Plus, they're relatively easy to care for, rewarding you with a stunning display in our mild, Mediterranean climate.

While we face challenges like drought and occasional water restrictions, the 235-day growing season gives us plenty of time to cultivate these beauties. By starting smart and staying attentive to their needs, you can enjoy a thriving chrysanthemum patch.

Starting chrysanthemum seeds indoors isn't strictly necessary here in Northern California, but it can give you a jump start, especially if you're after a specific variety. If you want to try it, begin in mid-January through early February, about eight weeks before you plan to transplant.

Use seed trays with a good seed-starting mix, providing warmth (a heat mat helps) and plenty of light. Remember to water from the bottom to avoid damping off – set the tray in a shallow dish of water and let the soil soak it up. Given our early spring, this head start ensures blooms later.

Transplanting your chrysanthemum seedlings outdoors should happen in mid-March through mid-April. Before you do, harden them off by gradually exposing them to outdoor conditions for about a week.

Space your plants 12-18 inches apart in a sunny spot. Keep an eye on the weather, as we can still get some unexpected cool snaps or late rain during this time. Alternatively, buying established starts from a local nursery or potted mums in the fall are great options.

Chrysanthemums need consistent moisture, but they don't like to be waterlogged, which is especially important to remember during our dry summers. Aim to water deeply at the base of the plant, avoiding wetting the foliage as much as possible. Given our low humidity, this helps prevent fungal diseases.

During the cooler spring and fall months, check the soil moisture by sticking your finger about two inches deep. If it feels dry, it's time to water. In the hotter summer months, you might need to water a couple of times a week, providing about an inch of water each time. Yellowing leaves can signal overwatering, while wilting indicates underwatering. A good layer of mulch around the base of the plant will help retain moisture and keep the soil cool, which is very helpful in our climate.

To encourage bushy growth and an abundance of flowers, pinch off the growing tips of your chrysanthemums every two to three weeks until around July 4th. This forces the plant to branch out, resulting in more blooms later in the season.

After July 4th, stop pinching to allow the flower buds to develop. As the first frost approaches in early November, you can cut back the foliage to tidy up the plant, but leave some growth to protect the crown through the winter.

You can expect your first chrysanthemum blooms sometime in late May through mid-July, depending on when you planted and the specific variety. These flowers are fall-blooming, so they'll last for weeks in the garden.

Cut the stems for bouquets when the flowers are fully open. When harvesting, use sharp, clean pruners to make a clean cut, which helps prevent disease. Regular deadheading of spent flowers encourages continuous blooming throughout the season. As the first frost approaches, you can bring any remaining blooms indoors to enjoy in a vase.

Here are some common problems you might encounter with chrysanthemums in Northern California:

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 within the leaves.
• What causes it: Larvae of small flies that burrow between leaf surfaces to feed.
• How to fix/prevent it: Remove and destroy affected leaves. Cover plants with floating row covers to 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.

Northern California Specific Challenges: The moderate-to-hot heat and dry summers of Northern California can stress chrysanthemums, making them more susceptible to spider mites and leaf miners. Consistent watering and good air circulation are key to preventing these problems. Pay extra attention during fire season, as smoke can also stress plants.

Chrysanthemums benefit from companion planting in your Northern California garden. Tomatoes and peppers make excellent companions because they deter nematodes in the soil, which can harm chrysanthemum roots. Lettuce planted nearby provides ground cover, helping to keep the soil cool and moist, which is especially beneficial during our dry summers.

Avoid planting chrysanthemums near fennel, as it can inhibit their growth.