Sweet Alyssum in Zone 4B — Midwest

Sweet Alyssum is a must-have in any Midwest garden. Those delicate, honey-scented flowers attract beneficial insects, acting as a living mulch around your veggies, and adding a touch of charm to your borders. Plus, it thrives in our fertile soil and provides beauty from early summer all the way into fall.

Sure, Midwest weather can be unpredictable. We've got to watch for late frosts and summer heat spells, but with a little planning and attention to timing, you can easily enjoy Sweet Alyssum throughout our 138-day growing season. It's all about working with the rhythm of our region.

Starting Sweet Alyssum indoors isn't essential, but it's an option, especially if you're itching to get a jump start on the season. Begin your seeds indoors from early to late March, about six weeks before you plan to transplant them outside. This gives you a head start before our moderate-to-late spring hits.

Use seed trays or small pots filled with a good seed-starting mix. Keep the soil consistently moist by bottom watering, which helps prevent damping off. Place the trays in a warm location and provide plenty of light, either from a sunny window or a grow light.

Once the danger of frost has passed – usually late April through early June here in the Midwest – it's time to transplant your Sweet Alyssum seedlings outdoors. Before planting, be sure to harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Plant your seedlings 6-8 inches apart in well-drained soil. Keep an eye on the weather forecast around transplant time; those late spring cold snaps can still happen. Water them well after planting to help them settle in.

Direct sowing Sweet Alyssum is a simple and effective way to get them growing. You can sow seeds directly into your garden beds anytime from late April through late July. Just make sure the soil temperature has warmed up a bit, ideally around 60-70°F.

Prepare the soil by loosening it and removing any weeds or rocks. Sow the seeds thinly and cover them with a light layer of soil. Keep the soil consistently moist until the seedlings emerge. Thin the seedlings to 6-8 inches apart once they are large enough to handle.

Sweet Alyssum thrives with consistent moisture, but it doesn't like to be waterlogged. In the Midwest, our wet-summer rainfall usually helps with this, but you'll need to pay attention during dry spells. A good rule of thumb is to water deeply once or twice a week, providing about an inch of water each time.

Use the "finger test" to check the soil moisture before watering. Stick your finger about two inches into the soil; if it feels dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our moderate-to-humid climate.

Signs of underwatering include wilting leaves and dry, crispy edges. Overwatering can lead to yellowing leaves and root rot. A layer of mulch around your plants can help retain moisture and suppress weeds, which is especially helpful during our summer heat spells.

Sweet Alyssum is pretty low-maintenance when it comes to pruning. However, if your plants start to look leggy or stop blooming in the middle of summer, a quick trim can work wonders.

Simply shear back the plants by about half, removing any dead or faded flowers. This will encourage fresh growth and a new flush of blooms. As the first frost approaches in late September, you can let the plants go to seed or pull them up, depending on your preference.

Sweet Alyssum isn't really a "harvestable" plant in the traditional sense. You won't be picking fruits or vegetables from it. Instead, you'll be enjoying its continuous bloom from early June through early October.

Since it's used as living mulch and a beneficial insect attractant, you're essentially harvesting its benefits all season long. Just keep the plants healthy and blooming by providing adequate water and occasional trimming. As the end of the season nears, you can let some of the flowers go to seed to encourage natural reseeding for next year.

Here are some common issues you might encounter with Sweet Alyssum in the Midwest:

Downy Mildew

• What it looks like: Yellow patches on the upper surface of the leaves, with a fuzzy, gray-purple growth on the undersides. Leaves will brown and die from the bottom up.
• What causes it: This oomycete pathogen thrives in cool, humid conditions, which we often get during our variable spring and sometimes in late summer. Spores spread by wind.
• How to fix/prevent it: Remove affected leaves immediately. Improve air circulation around your plants by spacing them properly. Water at the base of the plants, avoiding overhead watering. Consider using a copper-based fungicide as a preventative measure.

Dieback in Extreme Heat

• What it looks like: The plants may wilt, turn brown, and appear to be dying during periods of intense heat.
• What causes it: While Sweet Alyssum can tolerate some heat, our summer heat spells can sometimes be too much for it.
• How to fix/prevent it: Provide afternoon shade during the hottest part of the day. Water deeply and consistently to keep the soil moist. Mulching can also help to keep the soil cooler. Don't worry too much; the plants often recover when temperatures cool down.

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 small jumping beetles feed on the leaves, especially of young seedlings.
• How to fix/prevent it: Protect seedlings with row covers during their vulnerable stage. You can also try spraying with neem oil or coating the plants with kaolin clay. Interplanting with basil or catnip can also help to deter flea beetles.

Midwest Specific Challenges: Our moderate-to-hot summers combined with moderate-to-humid conditions and wet-summer rainfall can create a breeding ground for fungal diseases like downy mildew. Be vigilant about monitoring your plants and taking preventative measures to ensure they stay healthy and productive.

Sweet Alyssum makes a great companion plant for several vegetables in the Midwest garden. It attracts beneficial insects like hoverflies and lacewings, which help control aphids and other pests.

Good companions include:

• Broccoli: The beneficial insects attracted by Sweet Alyssum help protect broccoli from pests.
• Potato: Sweet Alyssum can act as a living mulch around potato plants, suppressing weeds and conserving moisture.
• Lettuce: The ground cover provided by Sweet Alyssum helps keep the soil cool and moist for lettuce, especially during our summer heat spells.

Avoid planting Sweet Alyssum near plants that are highly susceptible to flea beetles.