Chrysanthemum in Zone 5B — Northeast

Chrysanthemums, with their vibrant colors and late-season blooms, are a welcome sight in the Northeast garden. They bring a burst of life just as other plants are fading, and their hardy nature means you can enjoy their beauty well into the fall. Plus, the cool nights we often get here seem to intensify their colors!

Our short growing season and the occasional early frost can be a challenge, but with proper timing, you can absolutely grow beautiful chrysanthemums. Knowing we have about 168 days to work with helps focus our efforts.

Starting chrysanthemums from seed indoors isn't the most common approach, as they are widely available as established plants. However, if you're after a specific variety or just enjoy the process, you can start seeds indoors.

Begin in late February through mid March, about eight weeks before you plan to transplant outdoors. Use seed trays with a good seed-starting mix, provide warmth (a heat mat is helpful), and ensure they get plenty of light. Bottom watering is a great way to keep the seedlings moist without risking damping off, which can be a problem in our sometimes-damp springs.

Transplanting chrysanthemums outdoors should occur in late April through late May, once the risk of hard frost has passed. Remember to harden off your seedlings for about a week, gradually exposing them to outdoor conditions. This is especially important in the Northeast, where we can get some pretty wild temperature swings in the spring.

Space your plants 12-18 inches apart to allow for good air circulation. Alternatively, you can often find potted mums at local nurseries in the fall, or purchase starts in the spring, which can be a simpler way to get started.

Chrysanthemums need moderate watering, and consistent moisture is especially important during bud formation. In the Northeast's moderate-to-humid climate, aim to water deeply about once a week, unless we've had significant rainfall. Use the "finger test" – stick your finger about two inches into the soil; if it feels dry, it's time to water.

Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our humid summers. Aim for about an inch of water per week, supplementing rainfall as needed. Overwatering can lead to root rot, so watch for yellowing leaves or stunted growth. Underwatering will cause wilting and dry, crispy leaves.

A layer of mulch, like shredded bark or straw, can help retain moisture and suppress weeds, which is helpful in our often-rocky New England soil.

Pinching your chrysanthemums is key to getting a bushy plant with plenty of blooms. Start pinching the growing tips every 2-3 weeks, beginning when the plants are about 6 inches tall. You're removing the very tip of each stem, encouraging side shoots to develop.

Stop pinching around July 4th. This allows the plants to focus on developing flower buds for their fall display. As the first frost approaches in early October, you can cut back the plants to a few inches above the ground.

Chrysanthemums are fall-blooming, so expect your first harvest of flowers in early July through late August, about 70 days after transplanting. The flowers will last for weeks in the garden, providing a beautiful display.

Cut the flowers for bouquets when they are fully open. Use sharp, clean pruners to make the cuts, and try to cut early in the morning when the plants are well-hydrated. This will help the cut flowers last longer.

To encourage continued production, deadhead spent flowers regularly. As the first frost approaches, you can bring some of the cut flowers indoors to enjoy their beauty a little longer.

Here are some common problems you might encounter with chrysanthemums in the Northeast:

Aphids *What it looks like:* Clusters of tiny green, black, or white insects on stems and leaf undersides. You might also see sticky honeydew and curled or distorted new growth. *What causes it:* These sap-sucking insects reproduce rapidly, especially in warm weather. Ants may even farm them for the honeydew. *How to fix/prevent it:* A strong spray of water can knock them off. Encourage natural predators like ladybugs. For heavy infestations, use insecticidal soap or neem oil. Avoid excess nitrogen fertilizer.

Spider Mites *What it looks like:* Fine stippling (tiny white dots) on leaves, fine webbing on leaf undersides, and leaves turning bronze or yellow. *What causes it:* These tiny arachnids thrive in hot, dry conditions. *How to fix/prevent it:* A strong spray of water daily for a week is often enough. Increase humidity around the plants. Use neem oil or insecticidal soap.

Leaf Miners *What it looks like:* Tan, squiggly lines or blotches within the leaves. *What causes it:* The larvae of small flies burrow between the leaf surfaces, feeding on the tissue. *How to fix/prevent it:* Remove and destroy infested leaves. Cover plants with row covers to prevent the adult flies from laying eggs. Neem oil can also help.

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 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.

Northeast Specific Challenges: Our moderate heat, moderate-to-humid humidity, and even rainfall can create favorable conditions for fungal diseases like rust. Monitor your plants regularly and take action promptly to prevent problems from spreading.

Good companions for chrysanthemums include tomatoes and peppers. The strong scent of chrysanthemums can help deter pests that might bother your tomatoes and peppers. Lettuce is another good choice, as it can benefit from the partial shade provided by the taller chrysanthemum plants during the hottest part of the summer.

Avoid planting chrysanthemums near members of the cabbage family (broccoli, cabbage, kale, etc.). These plants can attract similar pests, potentially increasing the risk of infestation for both.