Nasturtium in Zone 5A — Mountain West

Nasturtiums are a fantastic choice for the Mountain West gardener. Their peppery flavor adds a zing to salads, and the vibrant flowers brighten any garden. Plus, in our high-altitude environment with intense sunlight, the cool nights actually enhance their flavor, making them even more delicious.

Our short growing season and unpredictable weather can be daunting, but nasturtiums are quick to mature, fitting nicely into our approximately 138-day window. By timing your planting correctly, you can enjoy a bountiful harvest of flowers, leaves, and even seeds, despite the challenges.

While nasturtiums thrive when direct sown, starting them indoors gives you a head start, especially if you're eager for an early harvest. Start your seeds indoors from mid-April through early May, about four weeks before you plan to transplant them outside. Use seed trays filled with well-draining potting mix, and keep them in a warm, sunny spot.

Bottom watering is a great way to keep the soil consistently moist without overwatering. Given our late springs here in the mountains, this indoor start can give you a jump on the season.

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 intense sun and cooler temperatures of our Mountain climate.

Space the plants about 10-12 inches apart to allow for their trailing growth habit. Even after the typical last frost, keep an eye on the forecast for unexpected cold snaps, which can still occur at our altitude.

Direct sowing is the preferred method for nasturtiums, as they don't always love being transplanted. Sow your seeds directly into the garden from mid-May through mid-July, after the last frost. Choose a spot with full sun to partial shade.

Prepare the soil by loosening it and removing any rocks or debris. Nasturtiums aren't picky about soil, and actually prefer slightly poor soil. Sow seeds 1/2 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 drought-tolerant and thrive in drier conditions, making them perfect for our arid Mountain West climate. Overwatering can lead to more foliage than flowers, which isn't what we want. During the peak of summer, when temperatures are consistently in the 80s, water deeply about once a week.

Use the "finger test" – stick your finger about two inches into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week. Water at the base of the plants to avoid wetting the leaves, which can lead to fungal issues in more humid climates.

During cooler spring and fall months, you may only need to water every two weeks, or even less if we get some rain. Signs of underwatering include wilting leaves and stunted growth. Overwatering can cause yellowing leaves and root rot. A light layer of mulch can help retain moisture in our dry climate and regulate soil temperature.

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

To harvest, simply snip the flowers or leaves off the plant with scissors or your fingers. Regular harvesting encourages continued production. As the first frost approaches in late September, harvest any remaining flowers and seed pods. The seed pods can be pickled and used as a caper substitute, extending your harvest even further.

Here are some common problems you might encounter with nasturtiums in the Mountain West:

Aphids

• What it looks like: Clusters of small, soft-bodied insects on stems and leaves, causing distorted growth.
• What causes it: Aphids are attracted to stressed plants. Our intense sun and alkaline soils can sometimes weaken plants, making them susceptible.
• How to fix/prevent it: Nasturtiums are often used as a trap crop for aphids, drawing them away from other plants. If infestations are heavy, spray with a strong jet of water or insecticidal soap.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green or brown caterpillars present.
• What causes it: These caterpillars are the larvae of cabbage white butterflies. They thrive in our moderate summer temperatures.
• 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: Tiny black flies swarming around the plants, especially in moist areas.
• What causes it: Black flies are attracted to damp soil and decaying organic matter. Overwatering or poor drainage can create favorable conditions for them.
• How to fix/prevent it: Improve drainage and avoid overwatering. Allow the soil surface to dry out between waterings.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity can sometimes stress nasturtiums, making them more susceptible to pests. The alkaline soil can also affect nutrient uptake. Regular monitoring and appropriate watering practices are key to keeping your nasturtiums healthy and productive.

Nasturtiums make excellent companions for various vegetables in the Mountain West garden. They are particularly beneficial when planted near:

• Tomatoes: Nasturtiums deter tomato hornworms and other pests that can damage tomato plants.
• Cucumbers: They attract beneficial insects that prey on cucumber beetles and other cucumber pests.
• Squash: Nasturtiums help repel squash bugs and squash vine borers.
• Broccoli and Cabbage: They can deter cabbage moths and other pests that attack brassicas.

Avoid planting nasturtiums near fennel, as they can inhibit each other's growth.