Nasturtium in Zone 4B — Great Plains

Nasturtiums are a fantastic addition to any Great Plains garden. The peppery flavor of the leaves and flowers adds a unique zest to salads and other dishes. Plus, their vibrant colors bring a cheerful touch to the garden, attracting pollinators and even acting as a trap crop for pests.

Our extreme weather and short 149-day growing season here can seem daunting, but nasturtiums are surprisingly resilient. With a little attention to timing, you can enjoy a bountiful harvest from early July through early October, even with our variable Plains climate.

Starting nasturtium seeds indoors is an option, but direct sowing is generally preferred since they don't love being transplanted. If you're itching to get a head start, sow seeds indoors from early to late April, about four weeks before you plan to transplant.

Use seed trays filled with well-draining potting mix and keep them in a warm, sunny location. Bottom watering helps prevent damping off, which can be a problem with our variable spring temperatures.

If you started your nasturtiums indoors, transplant them outdoors from mid May through early June, after the risk of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Space the plants 10-12 inches apart in a sunny spot. Keep an eye on the forecast – a late cold snap or hailstorm can set back your young plants, so be ready to cover them if needed.

Direct sowing is the easiest and most successful method for growing nasturtiums in the Great Plains. Wait until mid May, after the last expected frost, to sow your seeds directly into the garden. You can continue sowing seeds through late July for a continuous harvest.

Choose a location with full sun to part shade and prepare the soil by loosening it and removing any weeds. Sow seeds about ½ inch deep and 10-12 inches apart. Nasturtiums thrive in slightly poor soil, so don't worry about adding too much fertilizer.

Nasturtiums are wonderfully drought-tolerant, making them perfect for our variable rainfall patterns on the Plains. Overwatering is a more common problem than underwatering. They actually thrive in slightly poor, dry soil. Too much water can lead to more foliage and fewer flowers.

During the heat of summer, from late June through August, check the soil moisture regularly. Stick your finger about 2 inches deep into the soil. If it feels dry, it's time to water. Usually, about 1 inch of water per week is sufficient, either from rainfall or irrigation. Water at the base of the plants rather than overhead to minimize fungal issues, especially during periods of higher humidity.

Yellowing leaves can indicate overwatering, while wilting can signal underwatering. A layer of mulch, like straw or wood chips, can help retain soil moisture and regulate soil temperature during our extreme temperature swings.

You can expect your first nasturtium harvest from early July through early October, about 55 days after sowing. Both the flowers and leaves are edible. Harvest the flowers when they are fully open for the best flavor and visual appeal. The seed pods can also be harvested and pickled for a caper-like treat.

To harvest, gently snip the flowers or leaves with scissors or pinch them off with your fingers. Avoid pulling or tugging, which can damage the plant. Regular harvesting encourages more flower production, so keep picking them to enjoy a continuous supply.

As the first frost approaches in early October, harvest any remaining flowers and seed pods. The leaves will likely become less flavorful after a frost, but you can still use them in compost.

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

Aphids (intentional trap crop)

• What it looks like: Clusters of tiny green, black, or brown insects on stems and leaves, often causing distorted growth.
• What causes it: Aphids are attracted to stressed plants, and our variable weather can sometimes create stress.
• How to fix/prevent it: Nasturtiums can actually be used as a trap crop to draw aphids away from other plants. If infestations are heavy, spray with insecticidal soap or blast them off with a strong stream of water.

Cabbage Caterpillars

• What it looks like: Green caterpillars munching on leaves, leaving holes and ragged edges.
• What causes it: Cabbage white butterflies lay their eggs on the leaves, and the caterpillars hatch and feed.
• How to fix/prevent it: Handpick caterpillars off the plants. You can also use row covers to prevent butterflies from laying eggs.

Black Fly

• What it looks like: Small, dark flies clustered around new growth, causing stunted or distorted leaves.
• What causes it: Overwatering or poorly draining soil can attract black flies.
• How to fix/prevent it: Improve soil drainage and avoid overwatering. Allow the soil to dry out slightly between waterings.

Great Plains Specific Challenges: The hot summers and variable rainfall of the Great Plains can stress nasturtiums, making them more susceptible to pests and diseases if not properly managed. Consistent monitoring and appropriate watering practices are key.

Nasturtiums are great companions for many plants in the Great Plains garden. They attract beneficial insects and can even deter some pests.

Good companions include tomatoes, cucumbers, and squash. Nasturtiums can help repel squash bugs and cucumber beetles, protecting these vulnerable crops. They also benefit broccoli and cabbage by attracting cabbage white butterflies away from these brassicas.

Avoid planting nasturtiums near fennel, as they can inhibit each other's growth. Otherwise, nasturtiums are generally easygoing companions that add beauty and functionality to your garden.