Nasturtium in Zone 6B — Mountain West

Nasturtiums are a delight in our Mountain gardens! Their peppery flavor adds a zing to salads, the bright flowers are beautiful and edible, and they're surprisingly easy to grow. Plus, they attract beneficial insects while acting as a trap crop for pests that might otherwise bother your prized veggies.

Our high altitude, intense sun, and short growing season can be challenging, but nasturtiums are quick to mature, making them a great choice. With a 163-day growing season, you can get several harvests from nasturtiums. You just need to time things right.

Starting nasturtiums indoors is possible, but generally not preferred since they resent transplanting. However, if you're eager to get a head start, especially with our late springs, you can start seeds indoors late March through mid April, about four weeks before the last expected frost.

Use seed trays with a good seed-starting mix. Keep them warm and provide plenty of light – a sunny windowsill or grow lights work well. Bottom watering is a great way to keep the soil moist without overwatering and risking damping-off.

If you started your nasturtiums indoors, transplant them outdoors early to 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.

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, as late frosts can still happen in the mountains.

Direct sowing is the preferred method for nasturtiums, as they don't love being transplanted. Wait until early May through late July, after the last frost, to sow seeds directly into the garden.

Choose a sunny spot with well-drained soil. Nasturtiums aren't picky, and they'll even thrive in poor soil. Make sure the soil temperature is consistently above 55°F (13°C) for best germination. Plant seeds about ½ inch deep and space them 10-12 inches apart. Keep the soil moist until the seedlings emerge.

Nasturtiums are remarkably drought-tolerant and thrive with minimal watering, which is perfect for our dry Mountain climate. In fact, overwatering can lead to lush foliage at the expense of flowers, so less is definitely more.

During the cooler spring months, water only when the soil feels dry about two inches down – use the "finger test." Once the moderate-at-altitude summer heat kicks in, increase watering to about 1 inch per week if there's no rainfall. Water at the base of the plant to avoid wetting the leaves, which helps prevent fungal issues in our low-humidity environment.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch can help retain moisture in the soil and reduce the need for frequent watering, but don't overdo it.

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

Pick the flowers when they are fully open for the best flavor and visual appeal. For the leaves, harvest young, tender ones for a milder taste. If you want to try making caper-like pickles, harvest the seed pods when they are still green and plump. Regular harvesting encourages continued production throughout the season.

As the first frost approaches in early October, harvest any remaining flowers and leaves. The seed pods can still be harvested even after a light frost.

Here are some common problems you might encounter with nasturtiums in our Mountain gardens:

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, and our intense UV and alkaline soil can sometimes weaken plants.
• How to fix/prevent it: Nasturtiums are often used as a trap crop to draw aphids away from other plants. Check them frequently and spray with a strong stream of water to dislodge aphids. Insecticidal soap can also be used.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green droppings nearby. You might spot small, green caterpillars munching on the foliage.
• What causes it: Cabbage white butterflies lay their eggs on the leaves, and the caterpillars hatch and start feeding.
• How to fix/prevent it: Handpick caterpillars off the plants. Cover plants 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 can be found clustering on new growth, sucking sap and weakening the plant.
• What causes it: Like aphids, they are attracted to stressed plants.
• How to fix/prevent it: A strong blast of water from the hose can dislodge them. Insecticidal soap or neem oil can also be effective, but test on a small area first to ensure it doesn't damage the plant.

Mountain West Specific Challenges: Our moderate-at-altitude heat and low humidity generally benefit nasturtiums, as they prefer drier conditions. However, our alkaline soil can sometimes cause nutrient deficiencies, making plants more susceptible to pests. Amend your soil with compost to improve its fertility and pH balance.

Nasturtiums are excellent companion plants for several vegetables in our Mountain gardens. They attract beneficial insects and can deter pests.

Good companions:

• Tomato: Nasturtiums repel tomato hornworms and whiteflies, helping to protect your tomato crop.
• Cucumber: They deter cucumber beetles, which can transmit diseases.
• Squash: Nasturtiums help to repel squash bugs and vine borers.
• Broccoli and Cabbage: They can act as a trap crop for aphids and cabbage white butterflies, protecting your brassicas.

There aren't really any bad companions for Nasturtium.