Nasturtium in Zone 3A — Mountain West

Nasturtiums are a fantastic addition to any Mountain West garden. Their peppery leaves and vibrant flowers add a unique zest to salads, and they're incredibly versatile in the kitchen. Plus, the cheerful blooms are a welcome sight during our short but intense summer, bringing a burst of color and flavor to your high-altitude garden.

Our short 96-day growing season and alkaline soil can be a challenge, but nasturtiums are surprisingly adaptable. With a little planning and attention to timing, you can easily enjoy a bountiful harvest of these edible beauties before the first frost arrives in early September.

Starting nasturtiums indoors isn't essential, but it can give you a bit of a head start in our short season. If you choose to go this route, begin in early to late May, about four weeks before you plan to transplant. Use seed trays with well-draining soil, and keep them in a warm, sunny spot.

Bottom watering is ideal to prevent damping off. Remember, our springs are late, so don't jump the gun! You want to avoid any risk of frost after transplanting.

Transplant your nasturtium seedlings outdoors in early to late 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 nights we experience here.

Space the plants 10-12 inches apart to allow for good air circulation. Keep an eye on the weather forecast around transplant time; a late cold snap can still happen, even in June.

Direct sowing is the preferred method for nasturtiums, as they don't always love being transplanted. Wait until early to late June, when the soil has warmed up and all risk of frost is gone. 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 they actually thrive in slightly poor soil, so don't over-amend it. Sow seeds 10-12 inches apart, about half an inch deep, and keep the soil consistently moist until they germinate.

Nasturtiums are surprisingly drought-tolerant, which is a huge advantage in our dry Mountain West climate. Once established, they prefer infrequent, deep watering. In general, aim for about 1 inch of water per week, depending on rainfall.

Use the "finger test" to determine if they need watering: stick your finger about 2 inches into the soil. If it feels dry, it's time to water. Water at the base of the plants to avoid wetting the foliage, which can lead to fungal issues in our low-humidity environment.

Overwatering can cause lush foliage but fewer flowers, so err on the side of dryness. Signs of underwatering include wilting leaves, while yellowing leaves can indicate overwatering. A light layer of mulch, like shredded bark, can help retain moisture in our dry climate and regulate soil temperature.

You can expect your first harvest of nasturtium flowers and leaves from early August 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 encourage continued production. Harvest regularly to promote more flowering. As the first frost approaches in early September, harvest any remaining flowers and seed pods. You can pickle the seed pods for a caper-like treat!

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

Aphids

• What it looks like: Clusters of small, pear-shaped insects on stems and leaves, often accompanied by sticky honeydew.
• What causes it: Aphids are attracted to stressed plants, and our alkaline soil can sometimes contribute to nutrient imbalances.
• How to fix/prevent it: Nasturtiums are often used as a trap crop for aphids, drawing them away from other plants. You can also blast them off with a strong stream of water from the hose or introduce beneficial insects like ladybugs.

Cabbage Caterpillars

• What it looks like: Green caterpillars munching on leaves, leaving behind ragged holes.
• What causes it: Cabbage white butterflies lay their eggs on the plants, and the caterpillars hatch and feed.
• How to fix/prevent it: Handpick the caterpillars off the plants or use a Bacillus thuringiensis (Bt) spray, which is a natural insecticide.

Black Fly

• What it looks like: Tiny black flies swarming around the plants, especially in the soil.
• What causes it: Overwatering and poor drainage can create a breeding ground for black flies.
• How to fix/prevent it: Allow the soil to dry out between waterings and improve drainage. You can also use yellow sticky traps to catch the adult flies.

Mountain West Specific Challenges: Our intense sun can sometimes scorch the leaves, so providing some afternoon shade can be helpful. The low humidity generally keeps fungal diseases at bay, but be mindful of watering practices to avoid creating overly moist conditions.

Nasturtiums make great companions for a variety of plants in the Mountain West garden. They're particularly beneficial for:

• Tomatoes: Nasturtiums can help repel pests like whiteflies and aphids that often bother tomatoes.
• Cucumbers and Squash: Their sprawling growth habit can help suppress weeds and provide ground cover, conserving moisture in our dry climate.
• Broccoli and Cabbage: Nasturtiums deter cabbage moths, protecting these brassicas from caterpillar damage.

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