Sweet Alyssum in Zone 4A — Midwest

Sweet Alyssum is a fantastic addition to any Midwest garden. The delicate, honey-scented flowers not only add beauty, but they also attract beneficial insects that help keep your vegetable garden healthy. Plus, it's a surprisingly hardy little plant that can handle our variable Midwest weather.

While we do have to contend with cold winters and the occasional summer heat spell here in Zone 4A, Sweet Alyssum's relatively short growing season and tolerance for cooler temperatures make it a very manageable and rewarding plant to grow. With our 128-day growing season, you'll have plenty of time to enjoy its blooms.

Starting Sweet Alyssum indoors is an option, especially if you're eager to get a head start on the season. You can start seeds indoors from mid-March through early April, about 6 weeks before you plan to transplant them outside. This can be useful if you're aiming for earlier blooms, but direct sowing works just fine too.

Use seed trays or small pots filled with a good seed-starting mix. Keep them warm and provide plenty of light – a grow light works wonders, especially with our sometimes-cloudy spring weather. Don't forget to water from the bottom to avoid damping off. Considering our moderate-to-late spring, starting indoors can give you a jump.

Transplanting Sweet Alyssum seedlings outdoors can be done from early May through mid-June, once the danger of frost has passed. Be sure to harden off your seedlings for about a week before transplanting them. Give them gradually increasing exposure to the outdoors, so they can acclimate to the sun and wind.

Space the plants about 6-8 inches apart to allow for their spreading growth habit. Keep an eye on the weather forecast, as we can still get some unpredictable cold snaps in early May. A little protection with row covers can be helpful if a late frost is predicted.

Direct sowing Sweet Alyssum is a simple and effective method here in the Midwest. You can sow seeds directly into the garden from early May through late July. This gives you a wide window of opportunity to get them established.

Prepare the soil by loosening it and removing any weeds. Sweet Alyssum prefers well-drained soil, but it's adaptable. Scatter the seeds lightly over the soil surface and gently press them in. Keep the soil consistently moist until the seedlings emerge. Just keep in mind that the soil temperature needs to be warm enough for germination, so waiting until after the last expected frost is best. Plant them about 6-8 inches apart.

Sweet Alyssum needs moderate watering to thrive in our Midwest climate. While we get decent rainfall during the summer, it's important to pay attention to the specific needs of your plants. You don't want them drying out, especially during our occasional summer heat spells.

A good rule of thumb is to check the soil moisture about 2 inches down using the "finger test." If the soil feels dry, it's time to water. Aim for about 1 inch of water per week, either from rainfall or irrigation. During hotter periods, you may need to water more frequently.

Water at the base of the plants rather than overhead. This helps prevent fungal diseases, which can be a concern in our moderate-to-humid climate. Overwatering can lead to root rot, so watch for yellowing leaves or a generally unhealthy appearance. Underwatering will cause the plants to wilt and eventually turn brown. A layer of mulch around the base of the plants can help retain moisture and regulate soil temperature, which is especially helpful during those hot summer stretches.

Sweet Alyssum requires minimal pruning, but a little maintenance can keep it looking its best throughout the season. When the plants start to look leggy, usually in midsummer after the initial flush of blooms, shear them back by about half. Don't worry, they'll bounce back quickly with fresh growth and more flowers.

Just use a pair of scissors or garden shears to trim them back. Be sure to leave some green growth on the plants, as cutting them back too hard can weaken them. As the first frost approaches around mid-September, you can let the plants go to seed if you want them to self-sow for the following year. Otherwise, you can remove the plants and compost them.

Sweet Alyssum isn't typically harvested for its flowers, as it's primarily grown as an ornamental plant and beneficial insect attractant. However, you can expect the first blooms to appear about 45 days after planting, which means you should start seeing flowers from mid-June through late September if you plant at the right time. The flowers will continue to bloom throughout the growing season.

The flowers are small and fragrant, and they attract pollinators like bees and butterflies. You don't need to do anything special to encourage continued production. Just keep the plants watered and fertilized as needed, and shear them back if they start to get leggy. As the first frost approaches in mid-September, the plants will naturally slow down their growth and eventually die back.

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

Downy Mildew

• What it looks like: You'll see yellow patches on the tops of the 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 spreads in cool, humid conditions via wind-carried spores. It's more common during our wetter springs and early summers.
• How to fix/prevent it: Remove any affected leaves immediately to prevent the spread. Improve air circulation around the plants by spacing them properly. Water at the base of the plants, never overhead. You can also use copper-based fungicides as a preventative measure.

May Die Back in Extreme Heat

• What it looks like: The plant will stop growing and may even start to wilt or turn brown during periods of intense heat.
• What causes it: Sweet Alyssum prefers cooler temperatures and can struggle during our summer heat spells.
• How to fix/prevent it: Provide some afternoon shade during the hottest part of the day. Water deeply and regularly to keep the soil moist. Mulching can also help to keep the soil cooler. Don't worry, it will usually bounce back when the 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.
• What causes it: These are flea beetles, small jumping beetles that feed on the leaves of various plants. They're most damaging to young seedlings.
• How to fix/prevent it: Use row covers to protect seedlings during their vulnerable stage. You can also delay planting until the plants are larger and more resilient. Coating the plants with kaolin clay can deter the beetles. Neem oil spray is another option.

Midwest Specific Challenges: Our moderate-to-hot summers, combined with moderate-to-humid humidity and wet summers, can create ideal conditions for fungal diseases like downy mildew. Be sure to provide good air circulation and avoid overhead watering to minimize these issues. The summer heat spells can also stress the plants, so provide shade and water as needed.

Sweet Alyssum makes a great companion plant in the Midwest garden. It attracts beneficial insects like hoverflies and parasitic wasps, which can help control pests on other plants.

Good companions include:

• Broccoli: The beneficial insects attracted by Sweet Alyssum can help control pests that attack broccoli.
• Potato: Sweet Alyssum can act as a living mulch, helping to retain moisture and suppress weeds around potato plants.
• Lettuce: The ground cover habit of Sweet Alyssum can help to keep the soil cool and moist, which lettuce appreciates, especially during warmer weather.

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