Nasturtium in Zone 6B — Great Plains

Nasturtiums are a fantastic addition to any Great Plains garden. Their peppery leaves and vibrant flowers add a unique zest to salads, plus they attract pollinators to your tomatoes and squash. The fact that they thrive in our intense sunshine and tolerate our variable rainfall makes them a low-maintenance, high-reward choice.

Our region can throw some extreme weather your way, from spring temperature swings to summer hail. But with a 198-day growing season, you'll have plenty of time to enjoy these beauties if you time your planting right.

Starting nasturtiums indoors is possible, but honestly, it's usually not necessary here in the Plains. These plants really resent being transplanted. However, if you're eager to get a head start, especially in the northern Plains where the season is shorter, you can start seeds indoors from mid-March through early April, about four weeks before you plan to transplant.

Use seed trays filled with a well-draining potting mix and provide consistent warmth and light, either from a sunny window or grow lights. Bottom watering will help prevent damping off. Keep in mind that our variable spring weather might still delay your transplanting plans, so be flexible.

Transplanting nasturtiums should happen from mid-April through mid-May, once the risk of frost has passed. Before moving them outdoors, harden them off by gradually exposing them to the elements for about a week. This helps them adjust to our Plains wind and temperature fluctuations.

When transplanting, space them about 10-12 inches apart. Be gentle, as their roots are sensitive. Keep an eye on the forecast for any late-season cold snaps and be prepared to cover them if needed.

Direct sowing is the way to go with nasturtiums in our region. Wait until the soil has warmed up, typically from mid-April through mid-August. Sow seeds directly into well-drained soil, about half an inch deep and 10-12 inches apart.

Nasturtiums aren’t picky about soil, and in fact, they prefer soil that isn't too rich. Keep the soil consistently moist until the seedlings emerge, usually within a week or two. Direct sowing avoids disturbing their roots and gives them the best start in our prairie soil.

Nasturtiums are surprisingly drought-tolerant, which makes them perfect for our variable Plains climate. Overwatering is a far bigger concern than underwatering with these plants. Let the soil guide you.

During the spring, when rainfall is more frequent, you might not need to water them at all, unless we're in a dry spell. As the summer heat intensifies, check the soil moisture by sticking your finger about two inches deep. If it feels dry, give them a good soak, aiming for about an inch of water per week, delivered at the base of the plant to avoid wetting the foliage.

In the fall, as temperatures cool down, reduce watering again. Yellowing leaves can indicate overwatering, while wilting leaves suggest they need a drink. Mulching around the base of the plants with straw or wood chips can help retain moisture and regulate soil temperature.

You can expect your first harvest of nasturtium flowers and leaves from mid-June through late October, about 55 days after sowing. The flowers are ready to pick when they are fully open and vibrant in color. The leaves can be harvested at any time, but younger leaves tend to be more tender and flavorful.

When harvesting, use scissors or your fingers to gently snip off the flowers and leaves, being careful not to damage the plant. Regular harvesting encourages continued production. Even as our first frost approaches in late October, you can often extend the harvest by covering the plants on cold nights.

Here are a few common problems to watch out for 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 under leaves. Leaves may be sticky or distorted.
• What causes it: Aphids are attracted to stressed plants, but nasturtiums are often used as a trap crop to draw them away from other veggies.
• How to fix/prevent it: A strong blast of water from the hose can dislodge aphids. Encourage beneficial insects like ladybugs. Consider nasturtiums a sacrifice for your other plants.

Cabbage Caterpillars

• What it looks like: Green caterpillars chewing holes in leaves, leaving behind dark droppings.
• What causes it: Cabbage white butterflies lay their eggs on the underside of leaves, and the caterpillars hatch and start feeding.
• How to fix/prevent it: Handpick caterpillars off the plants. Cover plants with netting to prevent butterflies from laying eggs. Bacillus thuringiensis (Bt) is an effective organic control.

Black Fly

• What it looks like: Small, dark flies swarming around the plants, especially in damp conditions. Leaves may turn yellow or wilt.
• What causes it: Overwatering and poor air circulation create favorable conditions for black flies.
• How to fix/prevent it: Improve drainage and air circulation. Allow the soil to dry out between waterings. Use yellow sticky traps to catch adult flies.

Great Plains Specific Challenges: Our hot summers and variable rainfall can stress nasturtiums, making them more susceptible to pests. Consistent monitoring and proactive measures are key to keeping your plants healthy and productive.

Nasturtiums are great companions for many plants in the Great Plains garden. Plant them near tomatoes to attract aphids away from your prized tomatoes. They also benefit cucumbers and squash by deterring squash bugs and vine borers. Broccoli and cabbage also appreciate nasturtiums, as they can help repel cabbage moths. Avoid planting them near herbs like rosemary and sage, as they can compete for resources and attract unwanted pests to those herbs.