Chrysanthemum in Zone 9B — Southern California

Chrysanthemums bring a burst of color to your garden when many other flowers are fading, offering a welcome sight as we transition from the intense summer heat inland to our mild winters. They're fantastic for cut flower arrangements, adding a touch of autumn beauty to your home. Plus, successfully growing these beauties in your own backyard here in Southern California is incredibly rewarding.

While our region presents challenges like drought and occasional Santa Ana winds, the timing for growing chrysanthemums aligns well with our 334-day growing season. Starting indoors or buying established plants bypasses the worst of the summer heat, allowing you to enjoy their vibrant blooms during the cooler months.

Starting chrysanthemums from seed indoors is an option, but honestly, it's more common to either buy established plants in the fall or starts in the spring. If you're feeling ambitious, though, start seeds indoors from late November through mid December, about 8 weeks before you'd like to transplant them outside.

Use seed trays with a good seed-starting mix, keeping them consistently moist. Bottom watering is a great way to avoid damping off. You'll want a warm location and supplemental light since our daylight hours are shorter during this time of year. Remember, our spring character is very-early here, so starting early gives you a head start.

The ideal time to transplant your chrysanthemum seedlings outdoors is late January through late February. Before transplanting, harden them off for about a week by gradually exposing them to outdoor conditions. This helps them adjust to the sunlight and temperature changes.

Space your plants 12-18 inches apart to allow for good air circulation. Even though this is technically winter, we can sometimes experience unexpected warm spells, so keep an eye on the weather and water accordingly. You can also find potted mums in fall, or starts in spring at local nurseries.

Chrysanthemums need moderate watering, but it's crucial to get it right, especially with our SoCal climate. During the warmer months, from spring through fall, aim for about 1 inch of water per week, increasing it to 1.5 inches during any heat waves we might get. Use the finger test: if the top 2 inches of soil feel dry, it's time to water.

Water at the base of the plant to avoid wetting the foliage, as this can lead to fungal diseases in our low-to-moderate humidity. In the winter, when we get more rainfall, you can reduce watering accordingly. Watch for signs of underwatering, like wilting leaves, or overwatering, like yellowing leaves.

A good layer of mulch around your chrysanthemums helps retain moisture in the soil and keeps the roots cool during the summer heat inland. Just be sure to keep the mulch a few inches away from the stems to prevent rot.

Pruning chrysanthemums is key to getting those full, bushy plants with tons of blooms. Start pinching off the growing tips every 2-3 weeks, beginning in spring and continuing through July 4th. This encourages the plant to branch out and produce more flower buds.

Make sure you're only pinching off the very tips of the stems, leaving the rest of the plant intact. Stop pinching after July 4th, as this allows the flower buds to develop for your fall blooms. After the first frost around late December, you can cut back the plant to a few inches above the ground to prepare it for winter.

You can expect your first chrysanthemum harvest from early April through late May, depending on when you transplanted and the specific variety. The flowers are ready to harvest when they are fully open and the petals are firm. They’ll last for weeks in the garden.

To harvest, cut the stems at an angle, leaving several inches of stem on the plant to encourage continued production. Chrysanthemums are great for cut flower arrangements and will last a long time in a vase.

Even as the first frost approaches in late December, you can often continue to harvest flowers until a hard freeze hits. After that, cut back the plant as mentioned above and let it rest for the winter.

Here are some common problems you might encounter growing chrysanthemums in Southern 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. Leaves may be distorted or prematurely drop.
• What causes it: Larvae of small flies that tunnel between the upper and lower leaf surfaces to feed. More prevalent during warmer months.
• How to fix/prevent it: Remove and destroy affected leaves. Cover plants with lightweight row covers to prevent adult flies from laying eggs. Insecticidal soap or 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.

Southern California Specific Challenges: Our hot summer heat inland and low-to-moderate humidity can stress chrysanthemums, making them more susceptible to pests like spider mites and diseases like rust. The winter-wet rainfall can also create conditions favorable for fungal diseases if you're not careful with watering. Regular monitoring and proactive measures are key to keeping your plants healthy.

Chrysanthemums can benefit from companion planting. Tomatoes and peppers make good companions because they can provide some shade during the hottest part of the day, protecting the chrysanthemums from the intense summer heat. Lettuce also works well, as it prefers similar growing conditions and can act as a ground cover, helping to retain moisture in the soil.

Avoid planting chrysanthemums near anything that competes heavily for nutrients or water, especially during our dry periods.