Chrysanthemum in Zone 10B — Desert Southwest

Chrysanthemums, or mums, are a rewarding addition to any Desert Southwest garden. Their vibrant fall blooms bring a burst of color just as other plants are fading, extending the beauty of your garden. Plus, they make stunning cut flowers, bringing that beauty indoors.

Desert gardening presents unique challenges, but with proper timing, you can absolutely grow gorgeous mums. Our long, 349-day growing season gives you the flexibility to work around the extreme heat and make the most of our mild winters.

Starting Chrysanthemum seeds indoors isn't essential, but it can give you a head start, especially if you're after specific varieties. Sow seeds indoors from mid November through early December, about eight weeks before you plan to transplant. Use seed trays with a good seed-starting mix, keep them warm, and provide plenty of light – a grow light works wonders.

Bottom watering is key to prevent damping off. Since our spring arrives very early, getting a jump on the season indoors can give you the best blooms.

Transplant your Chrysanthemum seedlings outdoors from mid January through mid February. Before transplanting, harden them off for about a week by gradually exposing them to outdoor conditions. This helps them adjust to the sun and temperature differences.

Space plants 12-18 inches apart in well-draining soil. Keep an eye on the weather forecast; even though it's generally mild, a late cold snap can still happen. You can also buy potted mums in the fall, or starts in the spring.

Chrysanthemums need consistent moisture, but overwatering in our arid climate can lead to problems. A good rule of thumb is to water deeply when the top two inches of soil feel dry – use the finger test! During the cooler months, you might only need to water once a week, but during warmer periods, increase it to two or three times a week.

Always water at the base of the plant to avoid wetting the foliage. This helps prevent fungal diseases, especially with our occasional monsoon moisture. Aim for about an inch of water per week, adjusting based on rainfall and temperature.

Signs of underwatering include wilting leaves and dry, crispy edges. Overwatering can cause yellowing leaves and root rot. Mulching around your Chrysanthemums helps retain moisture and regulate soil temperature – use organic materials like shredded leaves or compost.

Pruning Chrysanthemums is essential for encouraging a bushy growth habit and abundant blooms. Start pinching the growing tips every 2-3 weeks until around July 4th. This encourages side shoots and more flowers.

After July 4th, stop pinching to allow the flower buds to develop. In late December, after the first frost, cut back the dead foliage to the ground to prepare the plant for winter dormancy.

You can expect your first harvest of Chrysanthemum flowers from late March through mid May. The flowers are ready to cut when they are fully open and the petals are firm. They'll last for weeks in the garden, adding color and interest.

To harvest, cut the stems at an angle, leaving several inches of stem on the plant. This encourages new growth and more blooms. Regular harvesting will keep your plants producing throughout the blooming season.

As the first frost approaches in late December, you can cut the remaining flowers to enjoy indoors. After the frost, cut back the plant to the ground.

Chrysanthemums can face a few common problems in the Desert Southwest, but with vigilance, you can keep your plants healthy.

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 within the leaves. Leaves may appear distorted or blistered. *What causes it:* Larvae of small flies that tunnel between leaf surfaces to feed. Common during warm weather. *How to fix/prevent it:* Remove and destroy affected leaves promptly. Cover plants with floating 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.

Desert Southwest Specific Challenges: Our extreme heat and low humidity can stress Chrysanthemums, making them more susceptible to pests and diseases. Monitor your plants closely, especially during the hottest months, and provide adequate water and shade as needed. The monsoon season can bring humidity spikes, increasing the risk of fungal diseases like rust. Good air circulation and avoiding overhead watering can help prevent these issues.

Good companions for Chrysanthemums include tomatoes and peppers. Tomatoes and peppers benefit from Chrysanthemums' pest-repelling properties. Lettuce also works well, as it can tolerate the partial shade provided by the Chrysanthemums, especially during the hottest part of the day.

Avoid planting Chrysanthemums near anything that requires highly alkaline soil. The competition can cause problems for both plants.