Nasturtium in Zone 7A — Mountain West

Nasturtiums are a fantastic addition to any high-altitude garden. Their peppery flavor adds a zing to salads and sandwiches, plus the vibrant flowers brighten up any space. They're incredibly versatile, providing both beauty and a culinary kick that thrives in our intense sun.

Growing anything in the Mountain West has its challenges, from our alkaline soil to the intense UV and short growing season. But with a little planning, you can easily enjoy nasturtiums throughout our 173-day season. Timing is key, and this guide will help you make the most of it.

Starting nasturtiums indoors is possible, but not usually necessary. Because they don't love being transplanted, direct sowing is generally the way to go. However, if you're eager to get a head start due to our short season, you can start seeds indoors from late March through mid April, about four weeks before the last expected frost.

Use seed trays with good drainage, and keep them in a warm spot with plenty of light – a south-facing window works well. Bottom watering is ideal to prevent damping off, especially with our cool spring temperatures. Remember, our late spring means you need to be patient!

If you started your nasturtiums indoors, transplant them outdoors from late April through late May, after 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 the intense sun and cooler nights we often experience.

Plant them 10-12 inches apart in well-draining soil. Even late into spring, keep an eye on the weather forecast – a sudden cold snap can still happen.

Direct sowing is the preferred method for nasturtiums in the Mountain West. Wait until late April through early August, once the soil has warmed up a bit and the risk of frost is minimal. Nasturtiums germinate best in soil temperatures around 65-70°F.

Prepare your soil by loosening it and adding some compost, although nasturtiums aren't too fussy about soil quality. Plant seeds about ½ inch deep and 10-12 inches apart. Keep the soil consistently moist until they germinate, which usually takes about a week or two.

Nasturtiums are drought-tolerant and actually prefer drier conditions, which is great for our dry Mountain West climate. Overwatering leads to more foliage and fewer flowers, so less is definitely more. During the peak of our moderate-at-altitude summer heat, you'll still need to water, but be mindful.

A good rule of thumb is to check the soil moisture about 2 inches deep using the "finger test." If it's dry, it's time to water. Aim for about ½ inch of water per week, depending on rainfall. Water at the base of the plants to avoid wetting the leaves, which can encourage fungal issues in other plants, even though our low humidity makes that less of a concern.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch, like straw or wood chips, can help retain moisture in the soil and regulate soil temperature, but don't overdo it since we want the soil to stay relatively dry.

You can expect your first harvest of nasturtium flowers and leaves from late June through early October, 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. Both have a peppery flavor that's delicious in salads.

To harvest, simply snip the flowers or leaves with scissors or your fingers, being careful not to damage the rest of the plant. Regular harvesting encourages more blooms and keeps the plants producing. As the first frost approaches in early October, harvest any remaining flowers and leaves. You can even pickle the green seed pods as a caper substitute.

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, often accompanied by sticky honeydew.
• What causes it: Aphids are attracted to stressed plants. Our alkaline soil and intense UV can sometimes stress plants, making them more susceptible.
• How to fix/prevent it: Nasturtiums are often used as a trap crop to attract aphids away from other plants. Regularly inspect your plants and wash off aphids with a strong stream of water. Introduce beneficial insects like ladybugs.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green caterpillars present.
• What causes it: Cabbage white butterflies lay their eggs on nasturtiums, and the caterpillars hatch and feed on the leaves.
• How to fix/prevent it: Handpick caterpillars off the plants. Cover plants with row covers to prevent butterflies from laying eggs. Use Bacillus thuringiensis (Bt) as a biological control.

Black Fly

• What it looks like: Similar to aphids, small black flies cluster on new growth.
• What causes it: Like aphids, they are attracted to stressed plants, especially in dry conditions.
• How to fix/prevent it: Improve air circulation around the plants. A strong spray of water can dislodge them. Use insecticidal soap as a last resort.

Mountain West Specific Challenges: The combination of our moderate-at-altitude heat, low humidity, and dry rainfall can sometimes stress nasturtiums, making them more susceptible to pests. Maintaining consistent (but not excessive) watering and ensuring good air circulation will help keep your plants healthy and productive.

Nasturtiums are excellent companion plants for several vegetables in the Mountain West garden:

• Tomatoes: Nasturtiums deter pests like whiteflies and aphids that can damage tomato plants.
• Cucumbers: They attract beneficial insects that pollinate cucumber flowers.
• Squash: Nasturtiums help repel squash bugs and vine borers.
• Broccoli and Cabbage: They deter cabbage moths, whose larvae can decimate these crops.

Avoid planting nasturtiums near fennel, as it can inhibit their growth.