Sweet Alyssum in Zone 7A — Desert Southwest

Sweet Alyssum is a fantastic addition to any Desert Southwest garden. It's not grown for eating, but it acts as a living mulch, attracts beneficial insects, and the delicate fragrance is a delight. Plus, the blankets of tiny flowers add a touch of softness to our often harsh landscape.

Don't let the extreme heat scare you away from growing Sweet Alyssum here. With smart timing and attention to watering, you can enjoy its beauty during our two growing seasons. Our long 230-day growing season gives you a couple of opportunities to get it right.

Starting Sweet Alyssum indoors is possible, but usually not necessary in our climate. If you're aiming for the earliest possible bloom, or had trouble with direct sowing in the past, it's worth considering. Start seeds indoors from late January through mid February, about 6 weeks before you plan to transplant.

Use seed trays with a good seed-starting mix and keep them consistently moist – bottom watering is your friend here. Provide warmth and plenty of light; a grow light is ideal. Remember, our spring can bring unexpected temperature swings, so starting indoors gives you a head start.

Transplant your Sweet Alyssum seedlings outdoors from mid March through late April. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the intense Desert Southwest sun and wind.

Plant seedlings 6-8 inches apart in well-draining soil. Keep an eye on the weather forecast; a late frost can still happen, so be prepared to cover your young plants if needed. Water them in well after transplanting.

Direct sowing Sweet Alyssum is the easiest method and works well in our climate. You can direct sow from mid March through mid September, giving you a wide window of opportunity. This makes it a good candidate for succession planting.

Prepare the soil by loosening it and removing any rocks or debris. Sweet Alyssum prefers soil temperatures around 60-70°F for optimal germination. Sow seeds thinly, about ¼ inch deep, and keep the soil consistently moist until they germinate. Thin seedlings to 6-8 inches apart.

Sweet Alyssum needs moderate watering, but it's not drought-tolerant, so pay attention to its needs, especially during our extreme heat. During the active growing seasons (spring and fall), water deeply about 2-3 times per week, providing about 1 inch of water each time. Use the finger test: if the top 2 inches of soil feel dry, it's time to water.

During the peak of summer, Sweet Alyssum may go dormant. Reduce watering to once a week, just enough to keep the soil from completely drying out. As monsoon moisture arrives, adjust watering accordingly. Avoid overhead watering, especially during humid periods, to prevent fungal diseases. Water at the base of the plants.

Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to yellowing leaves and root rot. Mulching around your plants with a layer of compost or wood chips helps retain moisture and regulate soil temperature, which is crucial in our desert environment.

Sweet Alyssum requires minimal pruning, but a little maintenance can keep it looking its best. The main goal is to prevent legginess and encourage new blooms.

Shear back your Sweet Alyssum plants by about half when they start to look sparse or leggy, usually in midsummer after the first flush of blooms. Don't worry, fresh growth and flowers will follow quickly. As the first frost approaches in early November, you can leave the plants in place; they may reseed themselves for the following spring.

Sweet Alyssum isn't harvested for consumption; it's more of a "set it and forget it" plant. You can expect blooms to start around late April if you planted early, and they'll continue through mid November, as long as you maintain adequate moisture.

Since it's used as living mulch and a beneficial insect attractant, there's no need to pick the flowers. Just enjoy their beauty and fragrance! To encourage continued production, deadhead spent flowers occasionally.

As the first frost approaches in early November, you can simply leave the plants in place. They may self-seed, giving you a head start for the next growing season.

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

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with fuzzy gray-purple growth on the undersides. Leaves brown and die from the bottom up.
• What causes it: An oomycete pathogen that thrives in cool, humid conditions, spreading via wind-carried spores.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation. Water at the base, avoiding overhead watering. Consider copper-based fungicides for prevention.

May Die Back in Extreme Heat

• What it looks like: Plants appear wilted, stunted, or even die back completely during the hottest part of the summer.
• What causes it: Our extreme heat and intense sun can be too much for Sweet Alyssum, especially if it's not adequately watered.
• How to fix/prevent it: Provide afternoon shade with shade cloth essential during the hottest months. Water deeply and regularly. Consider planting in a location that receives morning sun and afternoon shade.

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.
• What causes it: Small jumping beetles that feed on leaves, especially of young seedlings.
• How to fix/prevent it: Use row covers to protect seedlings. Delay planting until plants are larger and more resilient. Apply kaolin clay coating or neem oil spray. Interplant with basil or catnip.

Desert Southwest Specific Challenges: The extreme heat and arid humidity of the Desert Southwest can stress Sweet Alyssum, making it more susceptible to problems. Monsoon rainfall, while welcome, can also create humid conditions that favor fungal diseases like downy mildew. Providing adequate water, afternoon shade, and good air circulation are key to keeping your Sweet Alyssum healthy and thriving.

Sweet Alyssum makes a great companion plant for several vegetables in the Desert Southwest garden. It attracts beneficial insects that can help control pests.

Good companions include:

• Broccoli: Sweet Alyssum attracts hoverflies and other beneficial insects that prey on aphids, a common pest of broccoli.
• Potato: The flowering alyssum can attract beneficial insects that help control potato beetles.
• Lettuce: Sweet Alyssum acts as a living mulch, helping to keep the soil cool and moist, which is beneficial for lettuce in our hot climate.

Currently, there are no widely known bad companions for Sweet Alyssum.