Sweet Alyssum in Zone 5B — Mid-Atlantic

Sweet Alyssum is a fantastic addition to any Mid-Atlantic garden. Its delicate, honey-scented flowers attract beneficial insects, making it a great companion plant for vegetables. Plus, it thrives in our four seasons, adding beauty to both spring and fall gardens.

While our humid summers can be a challenge, and deer pressure is always a concern, Sweet Alyssum is relatively easy to grow here if you time things right. With a growing season around 178 days, you'll have plenty of time to enjoy its blooms.

Starting Sweet Alyssum indoors in the Mid-Atlantic is an option, especially if you want an early start. Begin around mid-February through early March, about six weeks before you plan to transplant. This is helpful if you want to ensure you have large, established plants going into the garden.

Use seed trays with a good seed-starting mix, and provide warmth and light – a heat mat and grow lights work wonders. Be sure to bottom water your seedlings to prevent damping off, a common problem in our humid spring climate. Our moderate spring weather generally allows for direct sowing, but indoor starting gives you a head start.

Transplant your Sweet Alyssum seedlings outdoors from early April through mid-May, after the last expected frost. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This is essential, given our variable spring weather; even a few hours of direct sun can shock tender seedlings.

Space the plants 6-8 inches apart to allow for their spreading growth habit. Keep an eye out for late frosts, which can still occur in early spring in the Mid-Atlantic. If frost is predicted, cover your transplants with a frost blanket.

Direct sowing Sweet Alyssum is a simple and effective method for Mid-Atlantic gardeners. You can sow seeds directly into the garden from early April through mid-August. This flexibility lets you stagger plantings for continuous blooms.

Prepare the soil by loosening it and removing any weeds. Sweet Alyssum prefers slightly cooler soil temperatures, so early spring and late summer sowings often do best. Sow seeds about ¼ inch deep and space them 6-8 inches apart. Keep the soil consistently moist until germination.

Sweet Alyssum needs moderate watering, which can be tricky in our humid Mid-Atlantic summers. Aim for about 1 inch of water per week, either from rainfall or irrigation. Stick your finger about 2 inches deep into the soil – if it feels dry, it's time to water.

In the spring and fall, when temperatures are milder, you may only need to water once a week, or even less if we've had rain. During the heat of summer, especially during dry spells, you might need to water every other day. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our humid climate.

Signs of underwatering include wilting leaves and dry soil. Overwatering can lead to yellowing leaves and root rot. A layer of mulch can help retain moisture and regulate soil temperature, which is beneficial in both our hot summers and cool springs.

Sweet Alyssum requires minimal pruning, but a little attention can keep it looking its best throughout the season. The main thing to watch for is legginess, which can happen in the heat of midsummer. When the plants start to look sparse and stretched, shear them back by about half.

Don't worry, this won't harm them! Fresh growth and flowers will follow quickly. In the late fall, as the first frost approaches around mid-October, you can let the plants go to seed, or pull them up to make way for fall crops.

Sweet Alyssum is primarily grown for its beauty and its ability to attract beneficial insects, so there's no real harvesting involved. Expect the first blooms around late May if you direct sow in early April. The plants will continue to flower throughout the summer and into the fall, often lasting until late October if the weather cooperates.

Since it acts as a living mulch, you'll be "harvesting" the benefits of weed suppression and improved soil health all season long. As the first frost approaches in mid-October, the plants will naturally decline. At that point, you can either leave them in place as a winter mulch or remove them.

Sweet Alyssum can face a few challenges in the Mid-Atlantic. Here are the most common:

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with fuzzy gray-purple growth on the undersides. Leaves brown and die from the bottom up.
• What causes it: An oomycete pathogen that thrives in cool, humid conditions. The spores spread easily by wind. Our humid springs and falls can create ideal conditions.
• How to fix/prevent it: Remove affected leaves immediately to prevent spread. Improve air circulation around plants. Water at the base, avoiding overhead watering. Consider a copper-based fungicide as a preventative measure.

Dieback in Extreme Heat

• What it looks like: Plants stop flowering, leaves turn brown and crispy, and the plant may appear to be dying.
• What causes it: Sweet Alyssum prefers cooler temperatures and can struggle in the peak of our Mid-Atlantic summers.
• How to fix/prevent it: Provide some afternoon shade during the hottest part of the day. Water deeply and regularly, especially during dry spells. Shear back the plants to encourage new growth when temperatures cool down.

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in the leaves. You might see small, dark beetles that jump when disturbed. Young seedlings are most susceptible.
• What causes it: Small jumping beetles that feed on leaves. They're often more prevalent during dry periods.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. Spray with kaolin clay or neem oil. Interplant with basil or catnip, which can deter flea beetles.

Mid-Atlantic Specific Challenges: Our moderate-to-hot summers and humid conditions can stress Sweet Alyssum. Provide adequate water, ensure good air circulation, and consider some afternoon shade to keep your plants thriving.

Sweet Alyssum makes a great companion plant in the Mid-Atlantic vegetable garden. It attracts beneficial insects like hoverflies and lacewings, which prey on aphids and other pests.

Good companions include:

• Broccoli: Sweet Alyssum attracts beneficial insects that help control broccoli pests like aphids and cabbage worms.
• Potato: The flowers attract predatory insects that feed on potato beetle larvae.
• Lettuce: Sweet Alyssum acts as a living mulch, suppressing weeds and keeping the soil cool, which is beneficial for lettuce, especially as our weather warms up.

Avoid planting Sweet Alyssum near plants that are highly susceptible to flea beetles, as it might attract them to the area.