Sweet Alyssum in Zone 9B — Desert Southwest

Sweet Alyssum is a winner in our Desert Southwest gardens. It's not just pretty with its delicate, honey-scented flowers, but it also acts as a living mulch, suppressing weeds and attracting beneficial insects that help keep pests away from your veggies. Plus, it thrives in both our spring and fall growing seasons, giving you months of blooms.

Our extreme heat and alkaline soil can be tough on plants, but Sweet Alyssum is surprisingly resilient if you time things right. With our long 313-day growing season, you have plenty of opportunities to get it established during the cooler months and enjoy its beauty.

Starting Sweet Alyssum indoors is an option, especially if you want a head start on blooms. Begin in early to late December, about six weeks before you plan to transplant. This gives them a chance to get going before our very-early spring kicks in.

Use seed trays with a good seed-starting mix, and provide warmth and light – a simple grow light works wonders. Water gently from the bottom to avoid disturbing the tiny seeds and prevent damping off.

Transplant your Sweet Alyssum seedlings outdoors in late January through early March. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind, preventing transplant shock.

Space the plants 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather; we can still get some chilly nights during this time, so be prepared to cover them if frost threatens.

Direct sowing is an easy way to grow Sweet Alyssum in the Desert Southwest. You can sow seeds from late January through mid October. Just make sure the soil is workable and the temperatures aren't too extreme.

Prepare the soil by loosening it and removing any rocks or debris. Scatter the seeds lightly over the surface and gently press them into the soil. Keep the soil consistently moist until the seedlings emerge, spacing them 6-8 inches apart as they grow. One thing to note: seeds may struggle to germinate during our hottest months.

Sweet Alyssum needs moderate watering, which can be tricky to get right in our desert climate. During the cooler spring and fall months, water deeply once or twice a 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.

As the extreme heat of summer arrives, Sweet Alyssum may go dormant. Reduce watering frequency, but don't let the soil completely dry out. When the monsoon moisture rolls in, watch your plants carefully. Increase watering if the soil dries out quickly, but make sure the soil drains well to avoid root rot.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our arid climate. Mulching around the plants with organic matter like compost helps retain moisture and regulate soil temperature. Yellowing leaves can indicate overwatering, while wilting leaves suggest underwatering.

Sweet Alyssum needs minimal pruning, but a little attention keeps it looking its best. In midsummer, when the plants get leggy from the extreme heat, shear them back by about half. This encourages fresh growth and a new flush of flowers when temperatures cool down.

Simply use sharp scissors or pruning shears to trim the plants, removing any dead or faded blooms. As the first frost approaches in mid- December, you can give the plants one last trim to tidy them up before winter dormancy.

Sweet Alyssum is primarily grown for its beauty and its benefits as a living mulch and insect attractant, so there's no need to "harvest" in the traditional sense. Expect the first blooms about 45 days after planting, and then enjoy continuous flowers from early March through late December.

Simply enjoy the blooms and the beneficial insects they attract. If you want to encourage more blooms, deadhead spent flowers by pinching them off. As the first frost approaches, you can leave the plants in place to decompose and add organic matter to the soil.

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, starting from the bottom of the plant.
• What causes it: This is caused by an oomycete pathogen that thrives in cool, humid conditions. While our humidity is generally low, monsoon season can bring periods of higher humidity that favor its spread.
• How to fix/prevent it: Remove affected leaves immediately and improve air circulation around the plants. Water at the base, avoiding overhead watering. Consider using a copper-based fungicide as a preventative measure.

May Die Back in Extreme Heat

• What it looks like: The plant stops growing and flowering. Leaves may turn brown and crispy, and the plant may appear to be dying.
• What causes it: Our extreme summer heat can be too much for Sweet Alyssum. The plant goes dormant to conserve energy and survive the heat.
• How to fix/prevent it: Provide afternoon shade with shade cloth, especially during the hottest months. Reduce watering frequency but don't let the soil dry out completely. The plant will usually recover and start growing again when temperatures cool down in the fall.

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: These are small jumping beetles that feed on the leaves. They're most damaging to young seedlings.
• How to fix/prevent it: Protect seedlings with row covers. Delay planting until plants are larger and more resilient. You can also try coating the plants with kaolin clay or spraying them with neem oil.

Desert Southwest Specific Challenges: The combination of extreme heat, arid humidity, and occasional monsoon rainfall can create unique challenges for growing Sweet Alyssum. The extreme heat can cause the plants to go dormant, while the monsoon humidity can increase the risk of fungal diseases. Careful watering, proper mulching, and providing afternoon shade are essential for success.

Sweet Alyssum is a great companion plant for many vegetables in the Desert Southwest. Plant it near broccoli to attract beneficial insects like hoverflies and lacewings, which prey on aphids and other pests that can damage your broccoli crop.

It also works well with potatoes and lettuce. Sweet Alyssum attracts pollinators that can improve potato yields, and its low-growing habit provides shade and helps retain moisture for lettuce, which can be sensitive to our intense sun. Avoid planting it near anything that prefers very dry soil, as Sweet Alyssum needs moderate moisture.