Sweet Alyssum in Zone 8B — Pacific Northwest

Sweet Alyssum is a delightful addition to any Pacific Northwest garden. Its delicate, honey-scented flowers attract beneficial insects, making it a fantastic companion plant in your veggie beds. Plus, it thrives in our mild summers and cool nights, adding beauty and fragrance from spring right through our long, mild fall.

While we might struggle with heat-loving plants, Sweet Alyssum is perfectly suited to our 210-day growing season. Don't let those overcast spring days fool you; with a little planning, you can enjoy a cascade of blooms for months.

Starting Sweet Alyssum indoors is an option, especially if you want a head start. Begin in early to late February, about six weeks before you plan to transplant. Use seed trays with a good seed-starting mix, and provide warmth and plenty of light, since our springs can be slow to warm up.

To avoid damping off, water from the bottom by setting the tray in a shallow dish of water until the soil surface is moist. This encourages strong root growth and keeps the foliage dry.

Transplant your Sweet Alyssum seedlings outdoors in late March through early May. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and brighter sunlight of our PNW spring.

Space the plants 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather forecast and protect young transplants from any late-season frosts that sometimes surprise us in early spring.

Direct sowing Sweet Alyssum is a simple and effective method, especially given our long growing season. Sow seeds directly into the garden from late March through early September. Choose a spot with full sun to part shade and prepare the soil by loosening it and removing any weeds.

Sweet Alyssum seeds are tiny, so sow them shallowly and keep the soil consistently moist until germination. Thin seedlings to 6-8 inches apart once they are large enough to handle. Direct sowing is a great option for succession planting, ensuring a continuous supply of blooms throughout the season.

Sweet Alyssum prefers moderate watering, but it's crucial to adjust your watering schedule to our specific Pacific Northwest climate. During our wet springs, you may barely need to water at all. Let rainfall do the work for you!

During the dry summer months, check the soil moisture regularly 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 irrigation. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid conditions.

Signs of underwatering include wilting leaves and dry, crispy edges. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, such as compost or shredded leaves, can help retain soil moisture and suppress weeds, reducing the need for frequent watering.

Sweet Alyssum requires minimal pruning but benefits from a mid-season refresh. When the plants start to look leggy, usually in midsummer, shear them back by about half. This encourages fresh growth and a new flush of flowers.

Don't be afraid to cut them back hard; they'll bounce back quickly. As the first frost approaches in early November, you can leave the plants in place to provide winter interest or remove them to tidy up the garden.

Sweet Alyssum is primarily grown for its beautiful flowers and its role as a beneficial insect attractant, so there's no real "harvesting" involved in the traditional sense. Expect the first blooms to appear about 45 days after planting, which means late May for spring plantings. The flowers will continue to bloom throughout the summer and into the fall, often until the first frost in early November.

To encourage continuous blooming, deadhead spent flowers by lightly shearing the plants. This prevents them from setting seed and encourages more flower production. At the end of the season, you can leave the plants in place to self-seed or collect the seeds for planting next year.

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

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with a fuzzy gray-purple growth on the undersides. Leaves brown and die from the bottom up.
• What causes it: This oomycete pathogen thrives in cool, humid conditions and spreads via wind-carried spores. Our wet springs and cool nights can create ideal conditions for downy mildew.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation by spacing plants adequately. Water at the base, never overhead. Consider using a copper-based fungicide as a preventative measure. Look for resistant varieties when purchasing seeds or plants.

May Die Back in Extreme Heat

• What it looks like: Plants may wilt, stop flowering, or even die back during periods of intense heat.
• What causes it: While our summers are generally mild, we can still experience occasional heat waves. Sweet Alyssum prefers cooler temperatures and can struggle when temperatures are consistently above 85°F.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Water deeply and consistently during heat waves. Mulch around the plants to help retain soil moisture. Don't worry too much; they often recover quickly once the temperatures cool down.

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in leaves. You might also see small, dark beetles that jump when disturbed. The worst damage is usually to young seedlings.
• What causes it: These small jumping beetles feed on the leaves, and they're most damaging to small, young plants.
• How to fix/prevent it: Protect seedlings with row covers during their vulnerable stage. Delay planting until plants are larger and more resilient. You can also try applying a kaolin clay coating or spraying with neem oil. Interplanting with basil or catnip may also help deter flea beetles.

Pacific Northwest Specific Challenges: Our mild summers and relatively dry conditions generally benefit Sweet Alyssum, but late blight can be a concern if you're growing tomatoes or potatoes nearby. Practice good garden hygiene and monitor your plants regularly for any signs of disease.

Sweet Alyssum is a fantastic companion plant in the Pacific Northwest garden! Plant it near:

• Broccoli: The sweet scent attracts beneficial insects like hoverflies and lacewings, which prey on aphids and other pests that can plague broccoli.
• Potatoes: Alyssum helps attract beneficial insects that can control potato beetles, a common pest in our region.
• Lettuce: As a ground cover, it helps retain moisture in the soil and suppress weeds, benefiting lettuce growth.

Avoid planting Sweet Alyssum near plants susceptible to the same diseases, although this is less of a concern for alyssum itself.