Sweet Alyssum in Zone 5A — Mountain West

Sweet Alyssum is a fantastic addition to any Mountain West garden. Its delicate, honey-scented flowers attract beneficial insects, making it a valuable companion plant in your veggie garden. Plus, it thrives in our intense sunlight and even tolerates those cool nights, adding beauty and a touch of sweetness to your short growing season.

Our high altitude, intense UV, and alkaline soil can be tough on some plants, but Sweet Alyssum is surprisingly resilient. With a little planning around our 138-day growing season, you can enjoy its blooms from early summer until the first frost.

Starting Sweet Alyssum indoors is an option, but often not necessary in our region. If you're itching to get a head start, aim for early to late March, about 6 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and provide warmth and bright light, mimicking the intense sun we get here, but without the harshness on tender seedlings. Bottom watering is your friend – it helps prevent damping-off disease. Just set the tray in a shallow dish of water until the surface of the soil is moist. Keep in mind our late springs; don't jump the gun too early!

Transplant your Sweet Alyssum seedlings outdoors in late April through early June, once the danger of hard frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to our intense UV and cooler nights.

Space the plants 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather forecast during this time. Those late spring temperature swings are common in the Mountains, so be prepared to cover your seedlings if a cold snap is predicted.

Direct sowing Sweet Alyssum is a simple and effective method in our region. Sow seeds directly into the garden from late April through late July. This allows you to extend your bloom season.

Prepare the soil by loosening it and removing any rocks or debris. Sweet Alyssum isn't too picky about soil, but adding some compost can help with moisture retention in our dry climate. Sow seeds thinly and keep the soil consistently moist until germination. Aim for 6-8 inches spacing between plants.

Watering Sweet Alyssum correctly is key in our dry Mountain West climate. While they need moderate moisture, they don't like soggy feet. The ideal watering schedule depends on rainfall, but a general rule is to provide about 1 inch of water per week.

Use the finger test: stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, as this can encourage fungal diseases, even in our low humidity.

During the hottest part of the summer (typically July and August), Sweet Alyssum may go dormant. Don't panic! Just reduce watering slightly. They'll bounce back when temperatures cool down in late summer. Signs of underwatering include wilting leaves and dry, cracked soil. Overwatering can lead to yellowing leaves and root rot. A layer of mulch, like straw or wood chips, will help retain moisture and keep the soil cool.

Sweet Alyssum requires minimal pruning, making it a low-maintenance choice for our busy Mountain gardens. The main reason to prune is to keep the plants from getting too leggy and to encourage more blooms.

When plants start to look sparse in midsummer, shear them back by about half. Don't worry, they'll quickly bounce back with fresh growth and more flowers. Avoid pruning too late in the season (after mid-August), as this may prevent them from setting buds for fall blooms before our early frosts arrive around late September.

Sweet Alyssum is primarily grown for its ornamental value and its ability to attract beneficial insects, so there's no traditional "harvest" involved. You can expect the first blooms about 45 days after planting, whether you started indoors or direct-sowed.

The plants will continuously flower throughout the growing season, from early June through early October, providing a constant source of nectar for pollinators. Simply enjoy the beauty and benefits they bring to your garden! As the first frost approaches in late September, you can let the plants go to seed naturally, allowing them to self-sow for the following year, or pull them up and compost them.

Here are a few common problems you might encounter with Sweet Alyssum in the Mountain West:

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with a fuzzy gray-purple growth on the undersides. Leaves will eventually brown and die, starting from the bottom of the plant.
• What causes it: This fungal disease thrives in cool, humid conditions. While our region is generally dry, downy mildew can occur during periods of prolonged wet weather or when plants are overcrowded, limiting air circulation.
• How to fix/prevent it: Remove affected leaves immediately and improve air circulation around the plants by spacing them properly. Water at the base of the plants, avoiding overhead watering. Copper-based fungicides can be used as a preventative measure.

May Die Back in Extreme Heat

• What it looks like: Wilting, browning, and overall decline, especially during the hottest part of the summer.
• What causes it: Even though our summers are moderate-at-altitude, Sweet Alyssum can struggle with prolonged periods of intense heat, especially when combined with our intense UV radiation.
• How to fix/prevent it: Provide afternoon shade during the hottest hours, especially for plants in full sun. Ensure adequate watering and consider adding mulch to help keep the soil cool. Don't overwater, as this can exacerbate the problem. They will return when the temperatures cool.

Flea Beetles

• What it looks like: Tiny round holes (shot-hole pattern) in the leaves. You might also see small, dark beetles jumping around when disturbed.
• What causes it: Flea beetles are small, jumping insects that feed on the leaves of various plants. They're most damaging to young seedlings.
• How to fix/prevent it: Row covers can protect seedlings during their vulnerable stage. Delay planting until plants are larger and more resilient. Kaolin clay can be sprayed on the plants to create a barrier. Neem oil can also be effective.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall can be both a blessing and a curse for Sweet Alyssum. While the low humidity helps prevent many fungal diseases, the intense sun and dry conditions can stress the plants, making them more susceptible to heat stress and insect infestations. Consistent watering and providing some afternoon shade can help mitigate these challenges.

Sweet Alyssum is a great companion plant for many vegetables in the Mountain West garden.

• Broccoli: Sweet Alyssum attracts beneficial insects like hoverflies and lacewings, which prey on aphids and other pests that can damage broccoli.
• Potato: The fragrant flowers of Sweet Alyssum can help deter potato beetles, a common pest in our region.
• Lettuce: Sweet Alyssum acts as a living mulch, helping to keep the soil cool and moist, which is beneficial for lettuce in our dry climate.

Avoid planting Sweet Alyssum near plants that are highly susceptible to flea beetles, as it can sometimes attract these pests.