Sweet Alyssum in Zone 7B — Desert Southwest

Sweet Alyssum is a low-growing, fragrant beauty that's right at home in our Desert Southwest gardens. It makes a pretty ground cover, attracts beneficial insects like crazy, and thrives in both our spring and fall growing seasons. It's a simple way to add some charm to your garden.

Sure, we've got extreme heat and alkaline soil to contend with, but with smart timing and a little extra care, Sweet Alyssum can flourish. Our long 245-day growing season gives you plenty of opportunity to enjoy these little flowers.

Starting Sweet Alyssum indoors is an option, but honestly, it's not always necessary here in the Desert Southwest. If you're itching to get a head start, aim to sow seeds indoors from mid January through early February, about six weeks before you plan to transplant. This can get you blooms going even earlier.

Use seed trays with a good seed-starting mix, keep them warm, and provide plenty of light – a simple grow light works wonders. Bottom watering helps prevent damping off, which can be a problem with tiny seedlings. Keep in mind that our spring season can arrive early, so watch the weather and be ready to move those seedlings out when conditions are right.

Once the danger of frost has passed – usually from early March through mid April – you can transplant your Sweet Alyssum seedlings outdoors. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to our intense Desert Southwest sun.

Space plants 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather; a late cold snap can still happen, so be prepared to cover your seedlings if needed.

Direct sowing Sweet Alyssum is a breeze in our climate, and often just as effective as starting indoors. You can sow seeds directly into the garden from early March through mid September. This gives you a long window of opportunity to establish these flowers.

Prepare the soil by loosening it and adding some compost. Sweet Alyssum isn't too picky, but well-draining soil is key. Sprinkle the tiny seeds lightly over the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge, then thin them to 6-8 inches apart.

Watering is crucial for Sweet Alyssum, especially during our hot, dry summers. While they're not drought-tolerant, they also don't like soggy feet. Finding that balance is key for success in our Desert Southwest gardens.

During the spring and fall, when temperatures are milder, water deeply about once a week, providing about 1 inch of water. In the heat of summer, you'll likely need to water more frequently, possibly every other day, especially during periods with no monsoon moisture. Use the finger test: if the top 2 inches of soil feel dry, it's time to water.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases. Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch around the plants helps retain moisture and keep the soil cool.

Sweet Alyssum requires minimal pruning, but a little maintenance can keep them looking their best. The main thing to watch for is legginess, especially during the summer heat.

When plants start to look stretched and sparse, usually in midsummer, shear them back by about half. Don't worry; they'll bounce back quickly with fresh growth and more flowers. As first frost approaches in mid- November, you can let the plants be; many will overwinter and return in the spring.

Sweet Alyssum isn't really a "harvest" kind of plant. You're not growing it for a specific crop, but for its continuous blooms and beneficial insect-attracting qualities. Expect the first flush of flowers about 45 days after planting, and then they'll just keep coming from mid April through late November.

The flowers are self-cleaning, so you don't need to deadhead them. Just enjoy the show! As the plants fade in late fall, you can leave them in place to provide winter interest and shelter for beneficial insects.

Even with its easygoing nature, Sweet Alyssum can run into a few problems in our Desert Southwest gardens. Here are the most common issues and how to deal with them:

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with a fuzzy, gray-purple growth on the undersides. Leaves will 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. Monsoon season can definitely bring this on!
• How to fix/prevent it: Remove affected leaves immediately to prevent spread. Improve air circulation around the plants. Water at the base, never overhead. You can use a copper-based fungicide as a preventative measure.

May Die Back in Extreme Heat

• What it looks like: The plant will look scorched and wilted, even with regular watering. Growth may slow or stop entirely.
• What causes it: Our extreme summer heat can be too much for Sweet Alyssum.
• How to fix/prevent it: Provide afternoon shade with shade cloth or plant in a location that gets partial shade. Keep the soil consistently moist. Don't be afraid to shear it back; it will often bounce back when temperatures cool down.

Flea Beetles

• What it looks like: Tiny, round holes (a "shot-hole" pattern) in the leaves. You might also see small, dark beetles that jump when disturbed.
• What causes it: These are flea beetles, small jumping pests that feed on plant leaves, especially young seedlings.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. Delay planting until plants are larger and more resilient. You can also try coating the leaves with kaolin clay or spraying with neem oil. Interplanting with basil or catnip can also help deter them.

Desert Southwest Specific Challenges The combination of extreme heat, arid humidity, and monsoon rainfall in the Desert Southwest can be tough on Sweet Alyssum. Be extra vigilant about watering during dry spells, and provide shade during the hottest part of the day. Good air circulation is key to preventing fungal diseases.

Sweet Alyssum makes a great companion plant in the Desert Southwest garden, attracting beneficial insects that help keep pests in check.

Good companions include broccoli, potato, and lettuce. Broccoli benefits from the beneficial insects attracted by Sweet Alyssum, which prey on cabbage worms and other pests. Potatoes enjoy the ground cover effect, which helps retain moisture in our dry climate. Lettuce also benefits from the shade and moisture retention provided by Sweet Alyssum.

Avoid planting Sweet Alyssum near plants that are highly susceptible to fungal diseases, as the dense foliage can trap moisture and create a humid microclimate.