Nasturtium in Zone 9A — Desert Southwest

Nasturtiums are a fantastic addition to any Desert Southwest garden. The peppery flavor of the leaves and flowers adds a zing to salads, and the bright colors bring a cheerful vibrancy to your garden. Plus, these beauties are surprisingly easy to grow and can even help protect your other plants.

Sure, our extreme heat and alkaline soil present challenges, but with a little planning, you can enjoy a bountiful harvest of Nasturtiums throughout our long 298-day growing season. The key is timing your planting to avoid the worst of the summer heat.

Starting Nasturtium indoors is possible, but honestly, it's usually not necessary here in the Desert Southwest. Since we have two growing seasons and a long frost-free period, direct sowing is generally more successful. That said, if you're itching to get a head start, you can start seeds indoors from mid January through early February, about four weeks before the last expected frost.

Use seed trays with well-draining potting mix and keep them in a warm spot with plenty of light. Bottom watering helps prevent damping off – simply set the tray in a shallow dish of water and let the soil soak it up. Given our very-early spring character, keep an eye on the weather and be ready to harden off your seedlings gradually.

Transplanting Nasturtiums outdoors should happen from late February through late March. Before you move them outside, give your seedlings a week of gradual outdoor exposure – this is called hardening off. Place them in a sheltered spot for a few hours each day, slowly increasing the time they spend outside.

When transplanting, space them about 10-12 inches apart. Keep an eye on the weather forecast and be prepared to protect them from any late frosts.

Direct sowing is the preferred method for Nasturtiums, as they don't love having their roots disturbed. You can direct sow from late February through early October, taking advantage of both our spring and fall growing seasons. This long window gives you plenty of flexibility.

Prepare your soil by loosening it and adding some compost. Nasturtiums aren't picky, but well-draining soil is a must. Sow the seeds about half an inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, which usually takes about a week.

Watering is where Desert Southwest gardening gets real. Nasturtiums are drought-tolerant and actually prefer slightly dry conditions. Overwatering is a much bigger problem than underwatering in our arid climate.

During the spring and fall growing seasons, water deeply about once a week, or when the top two inches of soil feel dry to the touch – use the finger test! In our extreme summer heat, you might need to water a bit more frequently, but be cautious. Aim for about ½ inch of water per week, adjusting as needed based on rainfall and temperature.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases, even in our low humidity. 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 and regulate soil temperature, but don't overdo it.

You can expect your first Nasturtium harvest from mid April through early December. Both the flowers and leaves are edible and ready to harvest when the flowers are fully open and the leaves are a vibrant green. Even the seed pods can be harvested and pickled for a caper-like treat.

To harvest, simply snip off the flowers or leaves with scissors or your fingers. Avoid pulling or tugging, which can damage the plant. Regular harvesting encourages more blooms and keeps the plant producing. As the first frost approaches in early December, harvest any remaining flowers and leaves to enjoy before the cold weather arrives.

Here are some common problems you might encounter with Nasturtiums in the Desert Southwest:

Aphids *What it looks like:* Clusters of small, pear-shaped insects on stems and leaves. Leaves may be sticky or distorted. *What causes it:* Aphids are attracted to stressed plants. In our dry climate, water stress can be a major factor. *How to fix/prevent it:* Nasturtiums are often used as a trap crop for aphids – they attract aphids away from other plants. If the infestation is heavy, blast them off with a strong stream of water.

Cabbage Caterpillars *What it looks like:* Holes in leaves, often with green droppings nearby. You might spot the caterpillars themselves – they're green and blend in well with the foliage. *What causes it:* Cabbage white butterflies lay their eggs on Nasturtiums, and the caterpillars hatch and start munching. *How to fix/prevent it:* Handpick the caterpillars off the plants. You can also use row covers to prevent the butterflies from laying eggs.

Black Fly *What it looks like:* Small, dark flies swarming around the plant, especially new growth. Leaves may be stunted or yellowed. *What causes it:* Black flies are attracted to moist soil and decaying organic matter. Overwatering or poor drainage can contribute to the problem. *How to fix/prevent it:* Improve drainage and avoid overwatering. You can also use yellow sticky traps to catch the flies.

Desert Southwest Specific Challenges: Our extreme heat can stress Nasturtiums, making them more susceptible to pests and diseases. Provide afternoon shade during the hottest months and ensure adequate, but not excessive, watering. Keep an eye out for sunscald on the leaves, especially if the plants are exposed to intense sunlight.

Nasturtiums are great companions for several plants in the Desert Southwest garden. They attract beneficial insects and can even repel some pests.

Good companions include tomatoes, cucumbers, and squash. Nasturtiums deter pests that bother these crops. They also help broccoli and cabbage by drawing cabbage white butterflies away from your precious brassicas.

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