Nasturtium in Zone 4A — Mountain West

Nasturtiums are a fantastic addition to any high-altitude garden. Their peppery leaves and vibrant flowers add a unique flavor to salads and bring a splash of color to your space. Plus, they're incredibly easy to grow, offering a rewarding experience for even the most novice Mountain West gardener.

Our short growing season and intense sunlight can be a challenge, but nasturtiums are surprisingly resilient. With a little planning and attention to timing, you can enjoy a bountiful harvest from these beauties within our 118-day window.

Starting nasturtiums indoors is possible, but honestly, it's often unnecessary in our climate. They resent transplanting, and direct sowing usually yields better results. However, if you're eager to get a head start, you can start seeds indoors from late April through mid May, about four weeks before our last expected frost.

Use seed trays with a well-draining potting mix, provide warmth, and ensure they receive plenty of light. Bottom watering helps prevent damping off, a common issue with seedlings. Just remember that spring can be slow to arrive in the Mountains, so be patient and avoid transplanting too early.

Transplanting nasturtiums requires a gentle touch. Aim to transplant them outdoors from late May through late June, once the danger of frost has passed. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week.

Choose a spot with full sun to partial shade and space the plants 10-12 inches apart. Keep an eye on the weather forecast, as late frosts can still occur. Be prepared to cover your young plants if temperatures dip unexpectedly.

Direct sowing is the preferred method for growing nasturtiums in the Mountain West. Wait until the soil has warmed up and all danger of frost has passed, typically from late May through early July.

Prepare the soil by loosening it and removing any weeds. Nasturtiums aren't picky about soil, so don't worry about adding too much fertilizer. Sow seeds 1/2 inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge.

Nasturtiums are drought-tolerant plants that thrive on neglect, making them perfect for our dry Mountain climate. Overwatering is a common mistake that can lead to more foliage and fewer flowers. Remember, less is more when it comes to watering these beauties.

During the peak of summer (moderate-at-altitude heat around 85°F), water deeply about once a week, providing roughly 1 inch of water. Use the finger test to check the soil moisture – if the top 2 inches are dry, it's time to water. Water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases, although our low humidity usually keeps that in check.

In spring and fall, when temperatures are cooler, you can reduce watering to once every 10-14 days. Signs of underwatering include wilting leaves, while yellowing leaves can indicate overwatering. A light layer of mulch can help retain moisture in the soil, but avoid heavy mulching, as it can trap too much moisture.

You can expect your first nasturtium harvest from late July through mid September, about 55 days after planting. Both the flowers and leaves are edible, so harvest them regularly to encourage continued production.

Pick the flowers when they are fully open for the best flavor and visual appeal. Harvest leaves as needed, snipping them off at the base of the stem. The seed pods can also be harvested and pickled for a caper-like treat. As our first frost approaches in mid- September, harvest any remaining flowers and seed pods to preserve them for later use.

Nasturtiums are generally easy to grow, but they can be susceptible to a few common problems in the Mountain West.

• Aphids (intentional trap crop)
• What it looks like: Clusters of tiny green, black, or white insects on stems and undersides of leaves; sticky honeydew; distorted growth.
• What causes it: Attracted to stressed plants; populations explode in warm, dry conditions which are common in our region.
• How to fix/prevent it: Nasturtiums act as a trap crop, drawing aphids away from other plants. Monitor regularly and spray with a strong jet of water or insecticidal soap if infestations become severe.
• Cabbage Caterpillars
• What it looks like: Green caterpillars chewing holes in leaves, leaving behind droppings.
• What causes it: Cabbage white butterflies lay eggs on plants in the cabbage family.
• How to fix/prevent it: Handpick caterpillars or use Bacillus thuringiensis (Bt), a biological insecticide. Row covers can prevent butterflies from laying eggs.
• Black Fly
• What it looks like: Small black flies that feed on sap, causing distorted growth and yellowing leaves.
• What causes it: Overwatering and poor soil drainage.
• How to fix/prevent it: Improve drainage, allow soil to dry out between waterings, and use yellow sticky traps to catch adults.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally benefit nasturtiums, reducing the risk of fungal diseases. However, the intense UV radiation can sometimes scorch leaves, so providing some afternoon shade can be helpful.

Nasturtiums are excellent companion plants for many vegetables in the Mountain West garden. They attract beneficial insects and can even repel certain pests.

Good companions include tomatoes, cucumbers, and squash. Nasturtiums deter squash bugs and whiteflies, while also attracting pollinators to help set fruit. They also benefit broccoli and cabbage by attracting aphids away from these crops, acting as a trap crop. Avoid planting nasturtiums near fennel, as it can inhibit their growth.