Nasturtium in Zone 4B — Midwest

Nasturtiums are a fantastic addition to any Midwest garden. The peppery flavor of the leaves and flowers adds a unique zing to salads, and they're beautiful spilling out of containers or rambling through your vegetable patch. Plus, they're incredibly easy to grow, bringing a lot of satisfaction for minimal effort.

Even with our variable spring weather and occasional summer heat spells, nasturtiums thrive here. You have a solid window to get them going after the threat of frost has passed. With our 138-day growing season, you'll have plenty of time to enjoy their vibrant colors and delicious flavors.

Starting nasturtiums indoors isn't essential, as they prefer direct sowing, but it can give you a head start if you're eager to see those first blooms. Begin in mid-April through early May, roughly four weeks before you plan to transplant outdoors. This aligns well with our moderate-to-late spring.

Use seed trays with a good seed-starting mix. Keep the soil consistently moist by bottom watering to avoid damping-off. Provide warmth and plenty of light, either from a sunny window or a grow light.

Transplant your nasturtium seedlings outdoors from mid-May through mid-June, once the danger of frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the Midwest weather.

Choose a spot with full sun to partial shade, and space the plants about 10-12 inches apart. Keep an eye on the weather forecast for any late frosts, and be prepared to cover your seedlings if necessary.

Direct sowing is the preferred method for nasturtiums, as they don't always love being transplanted. Wait until the soil has warmed up and all danger of frost is gone, typically mid-May through mid-July. This gives the soil a chance to warm up after our unpredictable spring.

Choose a sunny spot with well-drained soil. While nasturtiums aren't picky, loosening the soil and adding a bit of compost will give them a good start. Sow seeds about ½ inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge.

Nasturtiums are relatively drought-tolerant, so overwatering is a bigger concern than underwatering in our Midwest climate. They actually thrive in slightly poor, dry soil. Remember, too much water can lead to more leaves and fewer flowers.

During our typically wet summers, you might not need to water nasturtiums often at all. Check the soil moisture by sticking your finger about 2 inches deep. If it feels dry, give them a good soaking, aiming for about 1 inch of water per week, especially during summer heat spells. Water at the base of the plant to avoid fungal diseases, which can be a problem with our moderate-to-humid conditions.

Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. A light layer of mulch can help retain moisture and suppress weeds, but don't overdo it.

You can expect your first nasturtium harvest from mid-July through late September, about 55 days after sowing. Both the flowers and leaves are edible, offering a peppery flavor that adds a unique twist to salads and other dishes. The seed pods can also be pickled and used like capers.

Harvest flowers when they are fully open and leaves as needed. To encourage continued production, regularly harvest both the flowers and leaves. As our first frost approaches in late September, harvest any remaining flowers and leaves, and consider pickling the seed pods for a longer-lasting treat.

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

Aphids

• What it looks like: Clusters of small, soft-bodied insects on stems and undersides of leaves. Leaves may be sticky or distorted.
• What causes it: Aphids are attracted to stressed plants. Our variable spring weather can sometimes weaken plants, making them more susceptible.
• How to fix/prevent it: Nasturtiums can actually act as a trap crop, drawing aphids away from other plants. If the infestation is heavy, spray with a strong stream of water or use insecticidal soap.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green droppings nearby. You might see small green caterpillars munching on the leaves.
• What causes it: Cabbage white butterflies lay their eggs on nasturtium leaves, and the caterpillars hatch and feed.
• How to fix/prevent it: Handpick caterpillars off the plants. Cover plants with netting to prevent butterflies from laying eggs.

Black Fly

• What it looks like: Similar to aphids, but black in color and often found in large numbers on new growth.
• What causes it: Black fly infestations are often associated with warm, humid conditions.
• How to fix/prevent it: Spray plants with a strong stream of water to dislodge the black fly. Insecticidal soap can also be effective.

Midwest Specific Challenges: The moderate-to-hot heat and moderate-to-humid humidity of our summers can create ideal conditions for pests and diseases. Consistent monitoring and prompt action are key to keeping your nasturtiums healthy. Our wet summers can also lead to overwatering issues if you're not careful.

Nasturtiums make great companions for several vegetables in the Midwest garden. Plant them near tomatoes, cucumbers, and squash to help repel pests like squash bugs and aphids. They also benefit broccoli and cabbage by attracting cabbage white butterflies away from these brassicas. Avoid planting them near fennel, as it can inhibit their growth.