Nasturtium in Zone 6A — Mountain West

Nasturtiums are a fantastic addition to any Mountain West garden. Their peppery leaves and bright, cheerful flowers add a unique zest to salads and visual appeal to your garden beds. Plus, they're incredibly satisfying to grow in our short season because they're quick to mature and offer continuous harvests.

While our high altitude and intense sun here in Zone 6A can present challenges, nasturtiums are surprisingly well-suited to our climate. With a 153-day growing season, you have plenty of time to enjoy these beauties if you time your planting right.

Starting nasturtiums indoors is possible, but direct sowing is generally preferred since they don't love being transplanted. If you want a head start, begin in early to late April, about four weeks before the last expected frost.

Use seed trays with good drainage and a well-draining seed starting mix. Keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights works great. Bottom watering will help prevent damping off; just set the tray in a shallow dish of water and let the soil absorb it. Remember that our spring weather can be unpredictable, so hardening off is especially important.

Transplant your nasturtium seedlings outdoors in early May through early June, after the danger of frost has passed. Before planting, harden them off 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. Be gentle when transplanting, as their roots are delicate. Keep an eye on the weather forecast; a late-season cold snap can still happen in the mountains.

Direct sowing is the easiest and most successful method for growing nasturtiums in our region. Wait until early May through late July, once the soil has warmed up and the risk of frost is minimal.

Prepare the soil by loosening it and removing any weeds. Nasturtiums aren't picky, so you don't need to amend the soil much. Sow the seeds 1/2 inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, which usually takes about a week.

Nasturtiums are wonderfully drought-tolerant, making them perfect for our dry Mountain West climate. Overwatering is a much bigger concern than underwatering with these plants.

During the cooler spring months, you likely won't need to water them at all unless we're experiencing an unusually dry spell. As temperatures rise in the summer, check the soil moisture with the "finger test." Stick your finger about 2 inches into the soil; if it feels dry, it's time to water. Aim for about 1 inch of water per week, delivered at the base of the plant to avoid wetting the foliage in our low-humidity environment.

Yellowing leaves can be a sign of overwatering, while wilting leaves indicate underwatering. A light layer of mulch can help retain moisture and regulate soil temperature, but don't overdo it – good drainage is key.

You can expect your first nasturtium harvest in early July through early October, about 55 days after planting. Both the flowers and leaves are edible, so harvest them as needed.

The flowers are at their peak when fully open and vibrantly colored. Simply snip them off at the stem. For the leaves, harvest the younger, more tender ones for the best flavor. If you're interested in pickling the seed pods, harvest them when they're still green and firm.

To encourage continuous production, regularly harvest the flowers and leaves. As the first frost approaches in early October, harvest any remaining flowers and seed pods. The leaves will likely start to decline with the colder temperatures.

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

Aphids (intentional trap crop)

• What it looks like: Clusters of tiny green, black, or brown insects on the stems and undersides of leaves. Leaves may be sticky or distorted.
• What causes it: Aphids are attracted to nasturtiums, often more so than your other garden plants. They thrive in warm, dry conditions.
• How to fix/prevent it: Nasturtiums can act as a trap crop, drawing aphids away from your more valuable plants. Regularly inspect your nasturtiums and blast aphids off with a strong stream of water. You can also introduce beneficial insects like ladybugs.

Cabbage Caterpillars

• What it looks like: Holes in the leaves, often with green or brown droppings nearby. You might spot small green caterpillars on the plant.
• 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 your nasturtiums with row covers to prevent butterflies from laying eggs. Bacillus thuringiensis (Bt) is an effective organic control.

Black Fly

• What it looks like: Similar to aphids, these small black flies cluster on new growth, sucking sap and weakening the plant.
• What causes it: Black flies, like aphids, prefer warm, dry conditions.
• How to fix/prevent it: Blast them off with water, use insecticidal soap, or introduce beneficial insects.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry rainfall can actually benefit nasturtiums. They thrive in drier conditions, so you're less likely to encounter fungal diseases. However, the intense sun can sometimes scorch the leaves, so providing some afternoon shade can be helpful, especially at higher elevations.

Nasturtiums are excellent companion plants in the Mountain West garden. They attract pollinators and beneficial insects, while also acting as a trap crop for aphids.

Good companions include:

• Tomatoes: Nasturtiums deter tomato hornworms and other pests.
• Cucumbers: They help repel cucumber beetles.
• Squash: They attract squash vine borers away from your squash plants.
• Broccoli and Cabbage: They can help deter cabbage moths and other brassica pests.

Avoid planting nasturtiums near fennel, as they can inhibit each other's growth. Otherwise, nasturtiums are generally well-behaved and get along with most other garden plants.