Nasturtium in Zone 7A — Desert Southwest

Nasturtiums are a fantastic addition to any Desert Southwest garden. Their peppery leaves and vibrant flowers add a unique flavor to salads and a splash of color to your plate. Plus, they're incredibly easy to grow, offering a rewarding experience for both novice and experienced gardeners in our region.

While our extreme heat and arid conditions can be challenging, nasturtiums are surprisingly resilient when planted at the right time. With our long, 230-day growing season, you can enjoy two abundant harvests of these beauties, spring and fall, with a little summer survival mixed in.

Starting nasturtiums indoors is possible, but honestly, direct sowing is generally the way to go in our climate. Nasturtiums don't love having their roots disturbed. However, if you're eager to get a head start, you can start seeds indoors from late February through mid March, about four weeks before the last expected frost.

Use seed trays with a well-draining potting mix, and keep them in a warm spot with plenty of light – a sunny windowsill or under grow lights works well. Bottom watering is ideal to prevent damping off; just set the tray in a shallow dish of water and let the soil soak it up. Given our region's very-early spring character, this can give you a jump on the season.

If you started your nasturtiums indoors, transplant them outdoors from early to late April, once the danger of frost has passed. Before transplanting, harden off the seedlings by gradually exposing them to outdoor conditions for about a week.

Choose a sunny spot with well-draining soil, and space the plants 10-12 inches apart. Keep an eye on the weather forecast. A late cold snap can still happen during this time in the Desert Southwest, so be prepared to cover your seedlings if necessary.

Direct sowing is the preferred method for growing nasturtiums in the Desert Southwest. Wait until early April through early September to sow seeds directly into the ground.

Prepare the soil by loosening it and removing any rocks or debris. Nasturtiums aren't picky about soil, but good drainage is essential, especially with our occasional monsoon moisture. Plant seeds about ½ inch deep and space them 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge. Soil temps need to be at least 65-70°F for best germination.

Nasturtiums thrive on neglect, which makes them perfect for desert gardening. They prefer poor, dry soil and can easily be overwatered, leading to more foliage and fewer flowers. Knowing how to water is key to summer survival.

During the spring and fall growing seasons, water deeply but infrequently, allowing the soil to dry out between waterings. A good rule of thumb is to water when the top 2 inches of soil feel dry to the touch (the "finger test"). During the extreme heat of summer, you might need to water more frequently, but still avoid overwatering. Aim for about ½ inch of water per week.

Water at the base of the plants to avoid wetting the foliage, as our arid climate doesn't easily promote fungal diseases. Signs of underwatering include wilting leaves and stunted growth. Overwatering can cause yellowing leaves and root rot. A light layer of mulch, like decomposed granite, can help retain moisture without suffocating the roots.

You can expect your first harvest of nasturtium leaves and flowers in late May through early November, about 55 days after planting. Both leaves and flowers are edible and have a peppery flavor.

Harvest flowers when they are fully open and brightly colored. Snip them off at the stem. For leaves, harvest them as needed, taking care not to remove too many from a single plant at once. The seed pods are also edible and can be pickled for a caper-like treat. Regular harvesting encourages continued production. As the first frost approaches in early November, harvest any remaining flowers and seed pods to enjoy before the cold weather sets in.

Here are the top 3 problems you might encounter with nasturtiums in the Desert Southwest:

Aphids (intentional trap crop)

• What it looks like: Clusters of small, pear-shaped insects on stems and leaves, often accompanied by sticky honeydew.
• What causes it: Aphids are attracted to stressed plants, and in our arid climate, water stress can be a factor.
• How to fix/prevent it: Nasturtiums are often used as trap crops to attract aphids away from other plants. If the infestation is heavy, spray with a strong jet of water or use insecticidal soap.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green or brown caterpillars present.
• What causes it: Cabbage white butterflies lay their eggs on the leaves, and the caterpillars hatch and feed on the plant.
• How to fix/prevent it: Handpick caterpillars off the plants or use Bacillus thuringiensis (Bt), a natural bacteria that kills caterpillars.

Black Fly

• What it looks like: Tiny black flies swarming around the plant, particularly in the soil.
• What causes it: Overwatering or poorly draining soil creates a favorable environment for black fly larvae to thrive.
• How to fix/prevent it: Allow the soil to dry out between waterings and ensure good drainage. Use yellow sticky traps to catch adult flies.

Desert Southwest Specific Challenges: Our extreme heat and low humidity can stress nasturtiums, making them more susceptible to pests and diseases. Provide afternoon shade during the hottest months and ensure adequate watering to keep them healthy. The monsoon rainfall can also lead to fungal issues if the plants are not well-drained.

Nasturtiums are great companions for many plants in the Desert Southwest garden. They attract beneficial insects and can even act as a trap crop for aphids, drawing them away from your more vulnerable plants.

Good companions include tomatoes, cucumbers, and squash, as nasturtiums help repel pests that commonly attack these vegetables. Broccoli and cabbage also benefit from nasturtium companions, as the strong scent can deter cabbage moths. Avoid planting nasturtiums near fennel, as they can inhibit each other's growth.