Nasturtium in Zone 8A — Desert Southwest

Nasturtiums are a fantastic addition to any Desert Southwest garden. The peppery flavor of the leaves and flowers adds a unique zest to salads, and the bright colors bring a cheerful vibrancy to your garden. Plus, they're incredibly easy to grow, offering a high reward for minimal effort in our climate.

While our extreme heat and alkaline soil present unique challenges, nasturtiums are surprisingly resilient. With smart timing and minimal care, you can enjoy these beauties throughout our long, 265-day growing season.

Starting nasturtiums indoors is possible, but generally not necessary in our climate. If you want a head start, begin in early to late February, about four weeks before our average last frost. This might make sense if you have a very specific variety you want to ensure you get to grow.

Use seed trays with a good seed-starting mix and provide warmth and light. Bottom watering is key to prevent damping off; set the tray in a shallow dish of water until the top of the soil is moist. Remember, we often have a very-early spring, so keep an eye on the weather.

Transplant your nasturtium seedlings outdoors in mid-March through early April. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock from our intense sun.

Space them 10-12 inches apart in well-draining soil. Keep an eye on nighttime temperatures, as a late cold snap can still occur during this time of year.

Direct sowing is the preferred method for nasturtiums, as they don't love having their roots disturbed. Sow seeds mid-March through mid-September, giving you two distinct growing seasons.

Prepare the soil by loosening it and ensuring good drainage. Nasturtiums aren't picky about soil fertility. Plant seeds 1/2 inch deep and space them 10-12 inches apart. Keep the soil consistently moist until germination, which usually takes about a week.

Nasturtiums thrive on neglect, which makes them perfect for our arid Desert Southwest climate. Overwatering is a surefire way to get lots of leaves but few flowers. Once established, they are quite drought-tolerant.

During the hotter months, check the soil moisture by sticking your finger about 2 inches deep. If it's dry, give them a good soak, aiming for about 1 inch of water per week. In the cooler spring and fall, you can reduce watering frequency. Water at the base of the plant to avoid wetting the foliage, given our arid conditions, foliar disease is less of a concern.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch, like decomposed granite or shredded bark, can help retain moisture in the soil during our extreme heat.

You can expect your first nasturtium harvest in early May through late November. That's a long harvest window! Both the flowers and leaves are edible, so harvest them as needed.

Harvest flowers when they are fully open for the best flavor. Snip them off with scissors or your fingers, being careful not to damage the plant. To encourage continued production, regularly harvest both flowers and leaves.

As the first frost approaches in late November, harvest any remaining flowers and seed pods. The seed pods can be pickled and used like capers, extending your harvest even further!

Here are three common problems you might encounter with nasturtiums in the Desert Southwest:

Aphids (intentional trap crop) *What it looks like:* Clusters of tiny green, black, or brown insects on stems and leaves. Distorted or yellowing leaves. *What causes it:* Aphids are attracted to stressed plants, and while nasturtiums attract them, they serve as a trap crop to keep them off other plants. *How to fix/prevent it:* Nasturtiums are often planted as a trap crop, meaning they attract aphids away from your more valuable plants. You can blast aphids off with a strong stream of water from the hose.

Cabbage Caterpillars *What it looks like:* Holes in leaves, often with green droppings nearby. You might spot the caterpillars themselves, which are usually green. *What causes it:* Cabbage white butterflies lay their eggs on plants in the brassica family, and the caterpillars hatch and start munching. *How to fix/prevent it:* Handpick caterpillars off the plants. Use 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, you'll see clusters of small black flies on new growth, causing distorted leaves. *What causes it:* Like aphids, black flies are attracted to stressed plants and can quickly multiply in favorable conditions. *How to fix/prevent it:* Blast them off with a strong stream of water. Encourage beneficial insects like ladybugs and lacewings, which prey on black flies.

Desert Southwest Specific Challenges: Our extreme heat can stress nasturtiums, making them more susceptible to pests. Ensure adequate watering (but not overwatering!) and provide afternoon shade during the hottest part of the summer. The monsoon moisture can occasionally lead to fungal issues, but this is less common in our arid climate. Alkaline soil is generally not a problem for nasturtiums, as they tolerate a wide range of soil conditions.

Nasturtiums are great companion plants for several reasons, especially in our Desert Southwest gardens. Plant them near tomatoes, cucumbers, and squash to deter pests like squash bugs and aphids. They also do well near broccoli and cabbage, as they attract cabbage white butterflies away from these crops. Avoid planting them near herbs like rosemary and sage, as they can inhibit their growth. The strong scent of those herbs can also mask the nasturtiums, making them less effective as a trap crop.