Sweet Alyssum in Zone 5A — Midwest

Sweet Alyssum is a fantastic addition to any Midwest garden. It's not just pretty with its delicate, honey-scented flowers, but it also attracts beneficial insects like hoverflies that help keep pests in check. Plus, it thrives in our fertile soil and adds a lovely, cascading effect to borders or containers.

Midwest weather can be unpredictable, with late frosts and summer heat spells. But with a little planning and attention to timing, you can easily enjoy a season of beautiful Sweet Alyssum in our 157-day growing season.

Starting Sweet Alyssum indoors in the Midwest can give you a head start, but it's not always necessary. If you want blooms extra early, starting seeds indoors from late February through mid March, about 6 weeks before transplanting, works well.

Use seed trays with a good seed-starting mix. Keep them warm and provide plenty of light – a grow light is ideal. Gently bottom water to avoid disturbing the tiny seeds and prevent dampening off. Our moderate-to-late springs mean starting indoors can give you an edge, especially if you're aiming for early color.

Transplanting Sweet Alyssum outdoors in the Midwest should happen mid April through late May, once the danger of hard frost has passed. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space them 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather forecast; those variable spring temperatures can still dip unexpectedly. If a late frost is predicted, cover your transplants with a blanket or cloche for protection.

Direct sowing Sweet Alyssum is a straightforward option in the Midwest, and it often works just as well as starting indoors. Sow seeds mid April through early August, after the soil has warmed up a bit.

Prepare the soil by loosening it and removing any weeds. Scatter the seeds lightly over the surface and gently press them in. Keep the soil consistently moist until the seedlings emerge. Direct sowing is convenient, but remember that young seedlings are more vulnerable to pests and weather fluctuations.

Sweet Alyssum needs moderate watering, especially during our Midwest summers. While we get good rainfall, those summer heat spells can still dry things out quickly.

Check the soil moisture by using the "finger test" – stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or supplemental watering. During hot, dry periods, you might need to water more frequently.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our moderate-to-humid climate. Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch, like shredded bark, helps retain moisture and suppress weeds, which is helpful during our wet summers.

Sweet Alyssum requires minimal pruning, but a little maintenance keeps it looking its best. When the plants get leggy and stop blooming profusely in midsummer, shear them back by about half.

Use sharp scissors or pruning shears to remove the spent flowers and any excessively long stems. Don't worry about being too precise – Sweet Alyssum is very forgiving. After shearing, you'll see fresh growth and a new flush of flowers in no time. As the first frost approaches in early October, you can let the plants go to seed or pull them up and compost them.

You won't really "harvest" Sweet Alyssum in the traditional sense. This plant continuously flowers from early June through mid October, providing beauty and attracting beneficial insects all season long.

Instead of harvesting, enjoy the constant display of blooms and the benefits they bring to your garden. Since it's used as living mulch and a beneficial insect attractant, just let it do its thing. As the growing season winds down and the first frost approaches in early October, you can collect seeds for next year if you want, or simply let the plants fade away naturally.

Here are some common problems you might encounter with Sweet Alyssum in the Midwest:

Downy Mildew

• What it looks like: Yellow patches on the upper side of the leaves, with a fuzzy gray-purple growth on the undersides. The leaves will start to brown and die, starting from the bottom of the plant.
• What causes it: This is caused by an oomycete pathogen that thrives in cool, humid conditions. The spores are spread by wind, making it common after our wet-summer rain.
• How to fix/prevent it: Immediately remove any affected leaves. Improve air circulation around the plants by spacing them properly. Water at the base of the plants to avoid wetting the foliage. You can also use a copper-based fungicide as a preventative measure.

Heat Dieback

• What it looks like: Plants may wilt, turn brown, and appear to die back during periods of extreme heat.
• What causes it: While Sweet Alyssum prefers full sun, it can struggle during our summer heat spells.
• How to fix/prevent it: Provide some afternoon shade during the hottest part of the day. Ensure consistent watering, especially during dry spells. Mulch around the plants to help retain soil moisture and keep the roots cool. The plants usually recover when 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. Young seedlings are most susceptible to damage.
• What causes it: Flea beetles are small jumping beetles that feed on the leaves of various plants. They are particularly attracted to young, tender foliage.
• How to fix/prevent it: Protect seedlings with row covers during their vulnerable stage. Delay planting until the plants are larger and more resilient. You can also spray the plants with kaolin clay or neem oil. Interplanting with basil or catnip can help deter flea beetles.

Midwest Specific Challenges: The moderate-to-hot heat and moderate-to-humid humidity in the Midwest can create favorable conditions for fungal diseases like downy mildew. Be vigilant in monitoring your plants and take preventative measures to ensure they stay healthy.

Sweet Alyssum makes a great companion plant in the Midwest vegetable garden. It attracts beneficial insects that can help protect your crops.

Good companions include broccoli, potato, and lettuce. Broccoli benefits from the hoverflies and other pollinators attracted by Sweet Alyssum. Potato plants can benefit from the reduced pest pressure due to the beneficial insects. Lettuce appreciates the partial shade and cooler soil that Sweet Alyssum can provide. Avoid planting it near anything overly sensitive to moisture, as it prefers moderate watering.