Nasturtium in Zone 5B — Mountain West

Nasturtiums are a fantastic addition to any Mountain West garden. Their peppery leaves and bright flowers add a unique flavor to salads, and they're incredibly versatile in the kitchen. Plus, they’re beautiful and attract pollinators, bringing a splash of color to your garden during our brief but intense summer.

Our high altitude and short growing season (about 149 days) present some challenges, but with a little planning, you can easily grow these beauties. The key is timing your planting to take advantage of our long sunny days and relatively cool nights.

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

Use seed trays with well-draining potting mix, and keep them warm and consistently moist by bottom watering. Provide plenty of light – a sunny windowsill or grow lights work well. Be gentle when transplanting to avoid disturbing the roots.

If you started your nasturtiums indoors, transplant them outdoors from mid May through early June, after the danger of frost has passed. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Choose a sunny spot with well-drained soil, and space the plants 10-12 inches apart. Keep an eye on the weather – a late spring hailstorm or a sudden temperature swing can be tough on young transplants, so be prepared to cover them if necessary.

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

Prepare the soil by loosening it and removing any weeds. Sow seeds 1/2 inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, usually within a week or two.

Nasturtiums are surprisingly drought-tolerant, which makes them perfect for our dry Mountain West climate. Overwatering is a more common problem than underwatering, so err on the side of dryness.

During the peak of summer, when temperatures are around 85°F, water deeply about once a week, providing about 1 inch of water. Use the finger test – if the top 2 inches of soil are dry, it's time to water. In spring and fall, you may only need to water every couple of weeks, depending on rainfall. Water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in some situations, although our low humidity generally keeps this in check.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch, such as straw or wood chips, can help retain moisture and suppress weeds, but don't overdo it, as nasturtiums prefer drier conditions.

You can expect your first harvest of nasturtium flowers and leaves from early July through early October, about 55 days after planting. The flowers are ready to harvest when they are fully open and brightly colored.

Gently snip the flowers or leaves from the plant, being careful not to damage the stems. Regular harvesting encourages more blooms and keeps the plant producing throughout the season. As the first frost approaches in early October, harvest any remaining flowers and seed pods, which can be pickled and used like capers.

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

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 intense sun and alkaline soil can sometimes stress plants, making them more susceptible. How to fix/prevent it: Nasturtiums are often used as a trap crop for aphids, drawing them away from other plants. If infestations are heavy, spray with a strong blast of water from the hose or use insecticidal soap.

What it looks like: Chewed leaves with irregular holes, often with green caterpillars present. What causes it: These caterpillars are the larvae of cabbage white butterflies. They can be particularly problematic in our region due to the extended daylight hours during the growing season. 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 treatment.

What it looks like: Similar to aphids, these small black flies cluster on new growth, sucking sap and weakening the plant. What causes it: Like aphids, black flies thrive on stressed plants. Our dry conditions can sometimes make plants vulnerable. How to fix/prevent it: Spray with a strong jet of water to dislodge the flies. Insecticidal soap or neem oil can also be effective.

Mountain West Specific Challenges: Our moderate-at-altitude heat, low humidity, and dry climate generally benefit nasturtiums, as they prefer drier conditions. However, the intense UV radiation can sometimes stress the plants, so providing some afternoon shade can be helpful.

Nasturtiums are great companions for many plants in the Mountain West garden. They are particularly beneficial near tomatoes, cucumbers, and squash because they attract beneficial insects and can act as a trap crop for aphids, protecting your prized vegetables. Broccoli and cabbage also benefit from having nasturtiums nearby, as they can deter cabbage moths. Avoid planting nasturtiums near fennel, as they can inhibit each other's growth.