Nasturtium in Zone 4A — Midwest

Nasturtiums are a fantastic addition to any Midwest garden. Their peppery flavor adds a zing to salads, and the bright flowers are a beautiful edible garnish. Plus, they're relatively easy to grow here, offering a lot of satisfaction for minimal effort.

Our Midwest weather can be unpredictable, with late frosts and the occasional summer heat spells, but nasturtiums are adaptable enough to thrive with proper timing. With our 128-day growing season, you have plenty of time to enjoy these beauties.

While nasturtiums prefer direct sowing, starting them indoors is an option if you want a head start. Begin in mid April through early May, about four weeks before you plan to transplant outdoors. Use seed trays filled with a well-draining potting mix, and keep them in a warm, sunny spot or under grow lights.

A good tip is to water from the bottom by placing the tray in a shallow dish of water, letting the soil absorb what it needs. This encourages strong root growth. Just remember, our springs can be moderate-to-late, so keep an eye on the weather before moving them outside.

Transplant your nasturtium seedlings outdoors in late May through mid June, after the risk of frost has passed. 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.

When transplanting, space them about 10-12 inches apart. Keep an eye on the forecast, as late frosts can still happen in early June. A sudden cold snap can set them back, so be ready to cover them if needed.

Direct sowing is the preferred method for nasturtiums, as they don't always love being transplanted. Wait until late May through mid July, once the soil has warmed up and the danger of frost is gone. Choose a sunny spot with well-drained soil.

Before sowing, loosen the soil and remove any weeds. Plant the seeds about half an inch deep and space them 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, usually within a week or two.

Nasturtiums are relatively drought-tolerant and thrive in slightly poor soil, which is good news for us Midwest gardeners who often deal with clay soil. In fact, too much water or fertilizer can encourage leafy growth at the expense of flowers, so less is more.

During our wet-summer months, you might not need to water them at all unless we're experiencing a heat spell. Stick your finger about two inches deep into the soil; if it feels dry, it's time to water. Aim for about an inch of water per week, either from rainfall or irrigation.

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, while yellowing leaves can indicate overwatering. A layer of mulch can help retain moisture and suppress weeds, but don't overdo it – nasturtiums prefer drier conditions.

You can expect your first harvest of nasturtium flowers and leaves from mid July through mid September, about 55 days after planting. The flowers are ready to pick when they're fully open and vibrantly colored. The leaves can be harvested at any time.

To harvest, simply snip the flowers or leaves with scissors or your fingers, being careful not to damage the rest of the plant. Regular harvesting encourages continued production, so don't be shy about using them in your cooking. As the first frost approaches in mid- September, harvest any remaining flowers and seed pods to enjoy their peppery flavor or pickle the pods.

Even though nasturtiums are easy to grow, here are a few problems to watch out for in the Midwest:

Aphids

• What it looks like: Small, soft-bodied insects clustered on stems and leaves, often accompanied by sticky honeydew.
• What causes it: Aphids thrive in warm, humid conditions, which we often get during our summer heat spells.
• How to fix/prevent it: Nasturtiums can actually act as a trap crop, drawing aphids away from other plants. If infestations become heavy, spray with a strong stream of water or insecticidal soap.

Cabbage Caterpillars

• What it looks like: Green caterpillars feeding on leaves, leaving behind holes and droppings.
• What causes it: These caterpillars are the larvae of cabbage white butterflies, which are common in the Midwest.
• How to fix/prevent it: Handpick caterpillars when you see them. You can also use row covers to prevent butterflies from laying eggs on your plants.

Black Fly

• What it looks like: Small, black flies swarming around plants, especially new growth.
• What causes it: Similar to aphids, black flies are attracted to stressed plants and thrive in warm, humid conditions.
• How to fix/prevent it: Ensure your plants are healthy by providing adequate drainage and avoiding overwatering. Insecticidal soap can also help control infestations.

Midwest Specific Challenges: Our moderate-to-hot summers, combined with moderate-to-humid humidity and wet-summer rainfall, can create ideal conditions for pests and diseases. Monitor your plants regularly and take action promptly to prevent problems from getting out of hand.

Nasturtiums are great companion plants for many vegetables in the Midwest garden. Plant them near tomatoes, cucumbers, and squash to help deter pests like squash bugs and aphids. They also do well near broccoli and cabbage, as they attract cabbage white butterflies away from these crops. Avoid planting them near fennel, as it can inhibit their growth.