Sweet Alyssum in Zone 3B — Great Plains

Sweet Alyssum is a fantastic addition to any Great Plains garden. It's not just pretty; it attracts beneficial insects, acts as a living mulch, and its light, sweet fragrance is just lovely on those mild summer nights we get here. Plus, it's relatively easy to grow, providing a big payoff for our short growing season.

Our weather can be unpredictable, with extreme temperature swings and the ever-present risk of hail. But don't let that deter you. With a little planning, you can enjoy Sweet Alyssum from mid-June through late September, making the most of our 118-day growing season.

Starting Sweet Alyssum indoors can give you a jump start, especially if you're further north in Zone 3B where the season is shorter. Starting indoors makes sense if you want blooms as early as possible. Start seeds mid-March through early April, about six weeks before you plan to transplant.

Use seed trays or small pots with a good seed-starting mix. Keep the soil consistently moist by bottom watering – set the tray in a shallow dish of water and let the soil absorb it from the bottom. Place the trays in a warm spot and provide supplemental light. Keep in mind that spring here can be variable, so be prepared to adjust your schedule if we get an unexpected cold snap.

Transplant your Sweet Alyssum seedlings outdoors in early May through mid-June, once the danger of hard frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the stronger sun and wind we often experience here on the Plains.

Plant them 6-8 inches apart in well-drained soil. Keep an eye on the weather forecast. Even in May and June, we can get surprise temperature dips. Be ready to cover your transplants if a late frost threatens.

Direct sowing Sweet Alyssum is a simple option, especially if you're not looking for the earliest possible blooms. Sow seeds early May through mid-July, after the soil has warmed up a bit.

Prepare the soil by loosening it and removing any weeds. Gently press the tiny seeds into the soil; they need light to germinate. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to 6-8 inches apart once they are large enough to handle. Direct sowing is convenient, but remember that seedlings will be more vulnerable to flea beetles early on.

Sweet Alyssum needs moderate watering, which means keeping the soil consistently moist, but not soggy. During our hot Plains summers, you'll likely need to water more frequently, especially during prolonged dry spells. Aim for about an inch of water per week, either from rainfall or irrigation.

Use the "finger test" to check the soil moisture. Stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Water at the base of the plants rather than overhead to reduce the risk of fungal diseases in our low-to-moderate humidity.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and root rot. A layer of mulch around your plants can help retain moisture in the soil and suppress weeds – straw or shredded bark works well here.

Sweet Alyssum doesn't require a lot of pruning, but a little maintenance can keep it looking its best. When the plants start to look leggy or stop blooming as profusely, usually in midsummer, shear them back by about half. This encourages fresh growth and more flowers.

Use sharp scissors or pruning shears to make clean cuts. Remove any dead or yellowing leaves as you go. As the first frost approaches in mid-September, you can let the plants go to seed if you want them to self-sow for the following year. Otherwise, remove the plants after they have finished blooming.

Sweet Alyssum is primarily grown for its beauty and beneficial qualities, so you won't be "harvesting" it in the traditional sense. Expect the first blooms to appear about 45 days after planting, which usually means mid-June if you start early. The plants will continue to flower throughout the summer and into late September.

Enjoy the continuous display of delicate flowers and the pleasant fragrance. Because it's a living mulch, it suppresses weeds and holds moisture. As the first frost approaches in mid-September, allow the last blooms to fade and go to seed if you want them to self-sow, or simply remove the plants to prepare your garden for winter.

Here are a few common problems you might encounter with Sweet Alyssum in the Great Plains:

Downy Mildew

• What it looks like: You'll see yellow patches on the tops of leaves, with a fuzzy, gray-purple growth on the undersides. The leaves will eventually 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. The spores are spread by wind, which we have plenty of here on the Plains.
• How to fix/prevent it: Remove any affected leaves immediately. Improve air circulation around your plants by spacing them properly. Water at the base of the plants to avoid getting the foliage wet. Consider using a copper-based fungicide as a preventative measure.

May Die Back in Extreme Heat

• What it looks like: The plant may start to wilt, brown, and appear to be dying, especially during the hottest part of the summer.
• What causes it: Sweet Alyssum prefers cooler temperatures and can struggle in the extreme heat that's common during Plains summers.
• How to fix/prevent it: Provide some afternoon shade if possible. Ensure the plants are well-watered, especially during heat waves. Mulching can help keep the soil cooler. Don't worry too much; Sweet Alyssum often bounces back when temperatures cool down.

Flea Beetles

• What it looks like: You'll notice tiny, round holes (a "shot-hole" pattern) in the leaves. You might also see small, dark beetles that jump when disturbed. The damage is usually worst on young seedlings.
• What causes it: Flea beetles are small jumping beetles that feed on the leaves of various plants. They're most damaging to small, 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. You can also try coating the plants with kaolin clay or spraying them with neem oil. Interplanting with basil or catnip can help deter flea beetles.

Great Plains Specific Challenges: The hot, dry summers of the Great Plains can be tough on Sweet Alyssum. While it prefers moderate moisture, our variable rainfall means you'll need to pay close attention to watering. The combination of heat and wind can also dry out the soil quickly, so mulching is essential.

Sweet Alyssum makes a great companion plant in the Great Plains garden. Plant it near broccoli to attract beneficial insects like hoverflies, which prey on aphids that can damage your broccoli crop.

It also works well with potatoes. The alyssum acts as a living mulch, suppressing weeds and retaining moisture in the soil, which helps potatoes thrive. Lettuce also benefits from Sweet Alyssum planted nearby. The alyssum attracts pollinators, which can improve lettuce seed production if you're letting some of your lettuce go to seed. As for bad companions, there aren't any that are particularly problematic, but avoid planting Sweet Alyssum near anything that prefers very dry conditions, as it needs consistent moisture.