Sweet Alyssum in Zone 7A — Southeast

Sweet Alyssum is a fantastic addition to any Zone 7A garden here in the Southeast. It thrives in our long summer, producing a carpet of fragrant flowers that attract beneficial insects, plus it works great as a living mulch. The delicate scent is a treat, and the way it fills in spaces makes it a valuable player in both vegetable and flower beds.

Of course, our hot and humid summers present challenges, and disease pressure is always a concern. But with smart timing and attention to watering, you can easily enjoy a beautiful display of Sweet Alyssum throughout our long, 225-day growing season.

Starting Sweet Alyssum indoors isn't essential, but it can give you a jump start, especially if you're aiming for early blooms. Sow seeds indoors from late January through mid February, about six weeks before you plan to transplant. Use seed trays filled with a good seed-starting mix, and keep them consistently moist.

A little bottom watering helps prevent damping-off, which can be a problem in our humid climate. Place the trays in a warm spot with plenty of light – a sunny windowsill or under grow lights works well. Our springs here in the Southeast start off moderate, so getting a head start indoors lets you get ahead of the game.

Transplant your Sweet Alyssum seedlings outdoors from mid March through late April, once the danger of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Space plants 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather forecast around transplant time; a late cold snap can set them back, so be ready to cover them if needed.

Direct sowing Sweet Alyssum is a simple and effective method, especially here in the Southeast with our long growing season. You can direct sow from mid March through early September. The earlier you sow, the more blooms you'll get before the heat of summer kicks in.

Prepare the soil by loosening it and removing any weeds. Scatter the seeds thinly over the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to 6-8 inches apart once they're large enough to handle.

Sweet Alyssum needs moderate watering to thrive in our Southeast climate. While we get reliable rainfall during the summer months, it's important to monitor soil moisture, especially during dry spells. Stick your finger about two inches deep into the soil; if it feels dry, it's time to water.

Aim for about an inch of water per week, either from rainfall or irrigation. Water at the base of the plants rather than overhead to minimize fungal disease issues, which are common in our humid environment. Overwatering can lead to root rot, so make sure the soil is well-draining.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can cause yellowing leaves and a mushy stem. A layer of mulch helps retain moisture and suppress weeds, but be sure to keep it away from the stems to prevent rot.

Sweet Alyssum requires minimal pruning, but a little maintenance helps keep them looking their best. The main thing to watch for is legginess, which can happen in midsummer when the heat is at its peak. When plants get leggy, shear them back by about half.

Don't worry – they'll quickly bounce back with fresh growth and more flowers. At the end of the season, as our first frost approaches around early November, you can simply let the plants die back naturally or pull them up to make way for cool-season crops.

Sweet Alyssum isn't really a "harvest" crop in the traditional sense. It flowers continuously from late April through mid November, and doesn't require deadheading. Instead, it serves as a living mulch and a magnet for beneficial insects in your garden. The tiny flowers attract pollinators and predatory insects that help keep pests in check.

As the first frost approaches in early November, the plants will naturally slow down and eventually stop blooming. You can leave them in place to decompose and add organic matter to the soil, or pull them up to prepare the bed for winter.

Even though Sweet Alyssum is relatively easy to grow, you might encounter a few problems in our Southeast gardens:

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with a fuzzy gray-purple growth on the undersides. Leaves start to brown and die from the bottom up.
• What causes it: This is an oomycete pathogen that thrives in cool, humid conditions. The spores are carried by the wind, and different species affect different plants. Our humid springs and falls can create ideal conditions for downy mildew.
• How to fix/prevent it: Remove affected leaves immediately to prevent the spread. Improve air circulation around the plants by spacing them properly. Water at the base of the plants, avoiding overhead watering. You can also use a copper-based fungicide as a preventative measure. Look for resistant varieties when purchasing seeds.

Dieback in Extreme Heat

• What it looks like: Plants may wilt, turn brown, and appear to die back during the hottest part of the summer.
• What causes it: While Sweet Alyssum tolerates heat, our intense summer heat can be too much for them.
• How to fix/prevent it: Provide some afternoon shade during the hottest months. Make sure the plants are well-watered, but not waterlogged. Shearing them back can also encourage new growth once the temperatures cool down.

Flea Beetles

• What it looks like: Tiny, round holes (shot-hole pattern) in the leaves. You might also see small, dark beetles that jump when disturbed. The damage is usually worst on young seedlings.
• What causes it: These are small jumping beetles that feed on the leaves, especially of young plants.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more able to withstand the damage. Coating the leaves with kaolin clay can deter the beetles. Neem oil spray is another option. Interplanting with basil or catnip can also help repel flea beetles.

Southeast Specific Challenges: Our region's combination of hot heat, humid humidity, and wet-summer rainfall creates a perfect environment for fungal diseases like downy mildew. The clay soil common in many parts of the Southeast can also be challenging, as it can retain too much moisture and lead to root rot if drainage isn't improved. Be sure to amend your soil with compost and other organic matter to improve drainage and air circulation.

Sweet Alyssum makes a wonderful companion plant in the Southeast garden. It attracts beneficial insects that help control pests on other crops.

Good companions include:

• Broccoli: The beneficial insects attracted by Sweet Alyssum, like hoverflies and ladybugs, prey on aphids and other pests that can damage broccoli.
• Potato: Sweet Alyssum can help deter potato beetles and other pests that target potatoes.
• Lettuce: As a ground cover, Sweet Alyssum helps retain moisture in the soil and suppress weeds around lettuce plants.

I wouldn't recommend planting it near anything that prefers very dry soil, as Sweet Alyssum needs consistent moisture.