Sweet Alyssum in Zone 4B — Great Plains

Sweet Alyssum is a winner in our Zone 4B gardens. It's not just pretty, it attracts beneficial insects that help control pests on your veggies. Plus, it thrives in the intense sunshine we get here on the Plains, adding a touch of delicate beauty to even the toughest spots.

Sure, we deal with extreme temperature swings and the occasional hail, but Sweet Alyssum's relatively short maturity time means you can usually get a good show of blooms within our 149-day growing season. Careful timing and a little planning will set you up for success.

Starting Sweet Alyssum indoors is an option, especially if you want a head start on the season. Begin in early to late March, about six weeks before you plan to transplant. This gives them a good jump before our variable spring weather hits.

Use seed trays with a good seed-starting mix. Keep them warm and provide plenty of light – a grow light works wonders. Bottom watering will prevent damping off and keep the seedlings happy.

Transplanting Sweet Alyssum can happen from late April through early June. This gives you a good window to work with, depending on how quickly spring warms up. Before planting in the ground, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space them 6-8 inches apart to give them room to spread. Be mindful of any late frosts or strong winds we sometimes get in late spring; protection might be needed.

Direct sowing Sweet Alyssum is definitely doable here on the Plains, and honestly, sometimes the easiest route. Aim to sow from late April through early August. This gives you plenty of time to get a good bloom before fall.

Make sure the soil is warmed up a bit and prepped well. Scatter the seeds and lightly cover them. Thin seedlings to 6-8 inches apart once they emerge.

Sweet Alyssum needs moderate watering, but it's not drought-tolerant, so you have to pay attention, especially with our variable rainfall. During the heat of summer, it might go dormant if it gets too dry, but it usually bounces back when temperatures cool.

In spring and fall, when temperatures are milder, water deeply about once a week, giving them around an inch of water. During the hottest part of the summer, you might need to water every other day if we aren't getting rain. 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 helps prevent disease in our low-to-moderate humidity. Signs of underwatering include wilting and dry, crispy leaves. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch can help retain moisture and regulate soil temperature.

Sweet Alyssum doesn't need a ton of pruning, but a little maintenance helps keep it looking its best. If the plants start to look leggy or sparse in midsummer, 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 garden scissors to trim off the spent flower heads. As the first frost approaches in early October, you can let them go to seed if you want to try and get some volunteers next year.

Sweet Alyssum is grown more for its beauty and benefits than for harvesting. Expect the first blooms about 45 days after planting, and from early June through early October, you'll have a continuous display of flowers. It is used as a living mulch and attracts beneficial insects like hoverflies and lacewings.

No need to harvest individual flowers; just enjoy the show! If you want to collect seeds, let some of the flowers dry on the plant, then gently rub them to release the tiny seeds. As the season winds down and frost threatens in early October, you can let the plants go to seed naturally to encourage volunteers next spring.

Even though Sweet Alyssum is relatively easy to grow, here are a few problems you might encounter here on the Plains:

Downy Mildew

• What it looks like: Yellow patches on the tops of leaves, with fuzzy gray-purple growth underneath. Leaves start to brown and die from the bottom up.
• What causes it: This is caused by an oomycete pathogen that spreads through wind-carried spores in cool, humid conditions.
• How to fix/prevent it: Remove any affected leaves right away. Improve air circulation around the plants by spacing them properly. Water at the base, never overhead. Copper-based fungicides can help prevent it.

May Die Back in Extreme Heat

• What it looks like: The plant wilts and may appear to stop growing during the hottest days.
• What causes it: The extreme heat we get on the Plains can stress Sweet Alyssum, causing it to go dormant or even die back.
• How to fix/prevent it: Provide some afternoon shade during the hottest part of the day. Water deeply and regularly to keep the soil consistently moist. Mulch can also help regulate soil temperature.

Flea Beetles

• What it looks like: Tiny round holes (like a 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, especially of young seedlings.
• How to fix/prevent it: Use row covers to protect seedlings when they're most vulnerable. You can also delay planting until the plants are larger and more resilient. Kaolin clay can be sprayed on the plants as a deterrent, and neem oil can help control infestations.

Great Plains Specific Challenges: Our hot summers and variable rainfall can be tough on Sweet Alyssum. Make sure to provide adequate water during dry spells and consider providing some afternoon shade during the hottest part of the summer to prevent heat stress.

Sweet Alyssum is a great companion plant for many garden vegetables. Planting it near broccoli helps attract beneficial insects that prey on broccoli pests. It also works well with potatoes, as its spreading habit can act as a living mulch, helping to retain moisture in the soil. Lettuce also benefits from Sweet Alyssum's ability to attract pollinators and beneficial insects. I would avoid placing it near plants that are very susceptible to root rot in overly moist soil, as alyssum likes to be kept relatively moist.