Sweet Alyssum in Zone 8A — Pacific Northwest

Sweet Alyssum is a fantastic choice for us here in the PNW. Its delicate, honey-scented flowers attract beneficial insects to your garden, and it thrives in our mild summer conditions. Plus, it's edible! The flowers add a touch of sweetness to salads and desserts, offering both beauty and a little something extra from your garden.

While we don't have the scorching heat of other regions, our cool springs and occasional wet spells can present challenges. But with careful timing and a few simple strategies, you can easily grow Sweet Alyssum throughout our 203-day growing season.

Starting Sweet Alyssum indoors can give you a jumpstart, but it's not strictly necessary in our climate. If you want an earlier bloom, start seeds indoors from early to late February, about six weeks before you plan to transplant them.

Use seed trays filled with a good seed-starting mix and keep them consistently moist – bottom watering is a great way to avoid disturbing the tiny seeds. A warm location and grow lights will help germination, especially with our often overcast spring days.

Transplant your Sweet Alyssum seedlings outdoors from late March through early May, once the risk of hard frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space the plants 6-8 inches apart in well-draining soil. Keep an eye on the weather forecast during this 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 in our climate, and it's my personal preference. Sow seeds directly into the garden from late March through early September.

Prepare the soil by loosening it and removing any weeds. Lightly press the seeds into the soil, spacing them 6-8 inches apart. Keep the soil consistently moist until germination, which usually takes about a week. Direct sowing works well because our soil temperatures are usually moderate by late March.

Sweet Alyssum needs moderate watering to thrive, but it's not very drought-tolerant. In the PNW, this means paying attention to rainfall and adjusting your watering schedule accordingly.

During our wet springs, you may not need to water at all. Once the dry summer months arrive, check the soil moisture regularly using the "finger test" – if the top two inches of soil feel 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 to avoid wetting the foliage, which can encourage fungal diseases in our sometimes humid conditions. Signs of underwatering include wilting and yellowing leaves, while overwatering can lead to root rot. A light layer of mulch can help retain soil moisture and keep the roots cool during our mild summers.

Sweet Alyssum requires minimal pruning, making it an easy-care plant for PNW gardens. The main reason to prune is to keep the plants from getting leggy in midsummer.

When the plants start to look sparse or stretched out, shear them back by about half. Don't worry about being too precise; they'll bounce back quickly with fresh growth and flowers. As the first frost approaches in late October, you can leave the plants in place to overwinter or pull them up, depending on their condition.

Sweet Alyssum is primarily grown for its beauty and its benefits to the garden, not necessarily for a large harvest. However, the flowers are edible and can be used sparingly as a garnish or in salads.

You can expect the first flowers to appear around mid-May if you started indoors, or a bit later if you direct-sowed. Flowers will continue blooming through early November. Simply snip off the flower clusters as needed. To encourage continued production, deadhead spent flowers regularly. As the first frost approaches in late October, you can collect any remaining flowers before the plants are finished for the season.

Here are a few common problems to watch out for with Sweet Alyssum in the PNW:

Downy Mildew

• What it looks like: Yellow patches appear on the upper sides of the leaves, with fuzzy gray-purple growth on the undersides. The leaves will then brown and die, usually starting from the bottom of the plant.
• What causes it: This is caused by an oomycete pathogen that thrives in cool, humid conditions and spreads through wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately to prevent spread. Improve air circulation around the plants by spacing them adequately. Water at the base of the plant, avoiding overhead watering. For prevention, use copper-based fungicides. Consider planting resistant varieties if available.

May Die Back in Extreme Heat

• What it looks like: Plant growth stalls, leaves may yellow or brown, and flowering may cease entirely.
• What causes it: Although we have mild summers, a few days above 85°F can stress Sweet Alyssum.
• How to fix/prevent it: Provide afternoon shade during heat waves. Ensure adequate watering, but avoid overwatering. Mulch around the base of the plants to help retain soil moisture and regulate soil temperature.

Flea Beetles

• What it looks like: You'll see tiny, round holes (a "shot-hole" pattern) in the leaves. Small, dark beetles jump away quickly when disturbed. Seedlings are most susceptible.
• What causes it: These small jumping beetles feed on the leaves, particularly of young plants.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until the plants are larger and more resilient. Apply kaolin clay to coat the leaves, or spray with neem oil. Interplanting with basil or catnip can also help deter flea beetles. Ensure the plants are healthy and vigorous, as they can usually outgrow the damage.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer rainfall actually benefit Sweet Alyssum. However, our cool, wet springs can create conditions favorable for downy mildew. Be sure to provide good air circulation and avoid overhead watering to prevent this issue.

Sweet Alyssum makes an excellent companion plant in the PNW vegetable garden.

It pairs well with broccoli because its flowers attract beneficial insects like hoverflies and lacewings, which prey on aphids that can damage broccoli. It's also a great companion for potatoes; the alyssum attracts predatory wasps that help control potato beetles. Plant it near lettuce to attract pollinators, which can improve seed production if you're saving seeds, and the alyssum acts as a living mulch, suppressing weeds and keeping the soil cool.

Avoid planting it near any plants highly susceptible to downy mildew, as it could potentially spread the disease.