Nasturtium in Zone 3B — Mountain West

Nasturtiums are a fantastic addition to any Mountain West garden. Their peppery leaves and bright, edible flowers add a unique zest to salads and other dishes. Plus, they're surprisingly easy to grow, even with our intense sun and cool nights, bringing a splash of color and flavor to your high-altitude garden.

Our short growing season and alkaline soil can present challenges, but nasturtiums are resilient. With a little planning and attention to watering, you can enjoy a bountiful harvest within our 108-day window.

Starting nasturtiums indoors is an option, but not usually necessary in our climate. It's best if you're after an extra-early start or want to guarantee blooms before our first frost. If you choose to start indoors, begin in late April through mid May, about four weeks before you plan to transplant.

Use seed trays with a well-draining potting mix. Keep the soil consistently moist by bottom watering to avoid damping off, and provide plenty of light. Remember our spring weather can be unpredictable, so keep an eye on the forecast.

Transplant your nasturtium seedlings outdoors in early to late June, once the danger of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to our intense UV light and temperature swings.

Space the plants about 10-12 inches apart in a sunny or partially shaded spot. Even in June, be prepared for unexpected cold snaps; have some row covers ready just in case.

Direct sowing is the preferred method for nasturtiums, as they resent having their roots disturbed. Wait until early June through early July, after the last frost, to sow your seeds directly into the garden.

Prepare the soil by loosening it and removing any large rocks or debris. Nasturtiums aren’t picky about soil fertility, so don’t worry about adding too much amendment. Sow seeds about ½ inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge.

Nasturtiums thrive on neglect, which makes them perfect for our dry Mountain West climate. Overwatering is a common mistake that leads to more leaves than flowers. Remember, less is more with these plants.

During the peak of summer, when temperatures reach around 85°F, water deeply about once a week, or when the top two inches of soil feel dry to the touch. Use the finger test to check the soil moisture. Aim for about an inch of water per week. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal issues, even in our low humidity.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can cause yellowing leaves and root rot. A light layer of mulch, like straw or shredded bark, can help retain moisture and regulate soil temperature, but don't overdo it.

You can expect your first harvest of nasturtium flowers and leaves in late July through early September, about 55 days after planting. 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 from the plant with scissors or your fingers. Be gentle to avoid damaging the plant and encouraging continued production. Regularly harvesting flowers will encourage the plant to produce more blooms.

As our first frost approaches in early September, harvest any remaining flowers and seed pods. The seed pods can be pickled and used as a caper substitute.

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

Aphids (intentional trap crop)

• What it looks like: Clusters of tiny green, black, or brown insects on stems and leaves. Leaves may be sticky or distorted.
• What causes it: Aphids are attracted to nasturtiums, often more than other plants. They're common in gardens, and our alkaline soils don't deter them.
• How to fix/prevent it: Nasturtiums can act as a trap crop, drawing aphids away from your other vegetables. If infestations become too heavy, blast them off with a strong stream of water from your hose.

Cabbage Caterpillars

• What it looks like: Green caterpillars munching on leaves, leaving holes. You might also see small white butterflies fluttering around.
• What causes it: Cabbage white butterflies lay their eggs on nasturtiums. The caterpillars hatch and feed on the foliage.
• How to fix/prevent it: Handpick the caterpillars off the plants. Cover your nasturtiums with a fine mesh netting to prevent butterflies from laying eggs.

Black Fly

• What it looks like: Small, black, fly-like insects clustering around new growth. Leaves may yellow or wilt.
• What causes it: These pests suck sap from the plant, weakening it. They thrive in warm, dry conditions, which we often have in the Mountain West.
• How to fix/prevent it: Spray the plants with insecticidal soap. Ensure good air circulation around the plants to deter black flies.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally benefit nasturtiums, reducing the risk of fungal diseases. However, our intense UV light can sometimes scorch the leaves, so providing some afternoon shade can be helpful. The dry conditions mean you need to be diligent about watering, but be careful not to overwater.

Nasturtiums are great companions for several plants in the Mountain West garden:

• Tomatoes: Nasturtiums repel tomato hornworms and other pests that attack tomatoes, helping you get a better harvest.
• Cucumbers and Squash: They deter squash bugs and cucumber beetles, keeping these crops healthy and productive.
• Broccoli and Cabbage: Nasturtiums attract cabbage white butterflies away from your brassicas, reducing caterpillar damage.

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