Chrysanthemum in Zone 7B — Desert Southwest

Chrysanthemums bring late-season color to our Desert Southwest gardens when many other flowers are fading. Their vibrant blooms brighten fall bouquets and offer a cheerful contrast to the browns and golds of the desert landscape. Plus, they attract beneficial insects as your summer veggies are finishing up.

Growing mums here isn't without its challenges; the extreme heat and intense sun can be tough. But with careful timing and attention to watering, you can enjoy these beauties during our long, mild fall season. Our 245-day growing season gives you the time you need.

Starting Chrysanthemums from seed indoors is an option, but honestly, in our climate, it's often easier to buy starts or potted mums. If you want to give it a try, start seeds indoors from mid January through early February, about 8 weeks before you plan to transplant. Use seed trays and a good seed-starting mix.

Keep the trays warm and provide plenty of light—a grow light is a must. Water from the bottom to avoid damping off. Keep in mind that our spring can get an unexpected warm spell, so you might need to adjust your timing slightly.

Transplant your Chrysanthemums outdoors from mid March through mid April. Before you plant, harden them off by gradually exposing them to the outdoor conditions for about a week. This is especially important in our region, where the sun can be intense even in early spring.

Space them 12-18 inches apart in well-draining soil. Keep an eye on the weather; we can still get late frosts, so be ready to cover your plants if needed. Buying potted mums in the fall or starts in the spring is a reliable way to get mums in your garden.

Chrysanthemums need consistent moisture, but they don't like to be soggy. During our hot spring and early summer, water deeply about 2-3 times a week, providing about 1 inch of water each time. Use the finger test: if the top 2 inches of soil are dry, it's time to water.

As monsoon moisture arrives (if we're lucky!), adjust your watering schedule accordingly. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our arid climate. Signs of underwatering include wilting leaves and dry soil; overwatering can lead to yellowing leaves and root rot.

A good layer of mulch, like shredded bark, helps retain moisture and keeps the soil cooler during our extreme heat. Remember, even though we're a desert, consistent moisture is key for these plants to thrive.

Pinching your Chrysanthemums is essential for getting bushy plants with lots of blooms. Start pinching the growing tips every 2-3 weeks, beginning when the plants are about 6 inches tall. Pinch off the top set of leaves on each stem.

Stop pinching around July 4th to allow the flower buds to develop. After the first frost (around mid- November in our area), cut the plants back to about 6 inches above the ground. This helps them conserve energy over the winter.

You can expect your first Chrysanthemum blooms from late May through mid July, about 70 days after transplanting. The flowers last for weeks in the garden, providing a long season of color. Cut the flowers for bouquets when they are fully open.

To harvest, use sharp, clean pruners to cut the stems at an angle. Removing spent flowers encourages the plant to produce more blooms. As the first frost approaches in mid- November, cut any remaining flowers to enjoy indoors.

Here are some common problems you might encounter with Chrysanthemums in the Desert Southwest:

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 inside the leaves. Leaves may turn yellow or brown and drop prematurely.
• What causes it: Larvae of small flies that tunnel between the upper and lower leaf surfaces. More common in spring and early summer.
• How to fix/prevent it: Remove and destroy affected leaves. Cover plants with floating row covers to prevent flies from laying eggs. Systemic insecticides can be used in severe 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: The extreme heat and arid humidity of our region can stress Chrysanthemums, making them more susceptible to pests and diseases. Monitor your plants closely and take action quickly to prevent problems from escalating. While monsoon moisture can be welcome, it can also create conditions favorable for fungal diseases, so ensure good air circulation.

Chrysanthemums make good companions for tomatoes and peppers, as they can help repel certain pests like aphids that might otherwise attack your vegetable plants. The strong scent of Chrysanthemums is what deters the pests. They also pair well with lettuce, providing some shade during the hotter parts of the day.

Avoid planting Chrysanthemums near fennel, as it can inhibit their growth. Also, keep them away from sunflowers, which can compete for resources like water and nutrients, especially crucial in our dry climate.