Nasturtium in Zone 9B — Desert Southwest

Nasturtiums are a fantastic addition to any Desert Southwest garden. Their peppery leaves and vibrant flowers add a unique zest to salads, plus they attract beneficial insects to your veggie patch. You'll get a lot of satisfaction from their beauty and usefulness in our climate.

While our extreme heat and alkaline soil present challenges, nasturtiums are surprisingly resilient when planted at the right time. With our long 313-day growing season, you'll have plenty of opportunities to enjoy these beauties in spring, fall, and even winter.

Starting nasturtiums indoors is possible, but direct sowing is generally preferred since they don't love being transplanted. However, if you're aiming for a super early start, you can sow seeds indoors from early to late January, about four weeks before our transplant window opens.

Use seed trays with a good seed-starting mix, keep them warm, and provide plenty of light, either from a grow light or a sunny window. Bottom watering is a great way to keep the soil consistently moist without overwatering. Remember our spring character: very-early warmth can trick you, so keep an eye on the weather if you start early.

Transplant your nasturtium seedlings outdoors from mid February through mid March, after the last expected frost. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week. This will help them adjust to our intense sunlight and temperature swings.

Space the plants 10-12 inches apart in well-draining soil. Be mindful of late cold snaps that can still occur during this time. You might need to cover your young plants if a freeze is predicted.

Direct sowing is the easiest and most successful method for growing nasturtiums in the Desert Southwest. You can sow seeds directly into the garden from mid February through early October, giving you a long window of opportunity.

Choose a spot with full sun to partial shade and prepare the soil by loosening it and adding some compost. Nasturtiums aren't picky about soil, but good drainage is essential. Sow seeds 10-12 inches apart and about half an inch deep. Keep the soil consistently moist until the seeds germinate, which usually takes about a week.

Nasturtiums are drought-tolerant and thrive in drier conditions, which makes them perfect for desert gardening. The key is to avoid overwatering, especially during our monsoon season. Too much water can lead to more foliage than flowers.

During the cooler months of spring and fall, water deeply but infrequently – about once a week, or when the top two inches of soil feel dry to the touch. Use the finger test to make sure you're not overdoing it. In the extreme summer heat, you might need to water twice a week, but always check the soil moisture first. Aim for about 1 inch of water per week.

Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our arid climate. Signs of underwatering include wilting leaves, while overwatering can cause yellowing leaves and root rot. A light layer of mulch, like decomposed granite, can help retain moisture in the soil and regulate soil temperature.

You can start harvesting nasturtiums from early April through mid December, roughly 55 days after planting. Both the flowers and leaves are edible, so keep an eye out for fully opened blooms and healthy-looking leaves.

Harvest flowers in the morning when they are at their peak. Snip the stems just above a leaf node to encourage more blooms. For leaves, harvest as needed, taking only a few from each plant to allow it to continue growing. The seed pods can also be harvested and pickled for a caper-like treat.

Nasturtiums are continuous bloomers, so regular harvesting will encourage more flowers. As our first frost approaches in mid- December, harvest any remaining flowers and seed pods. The plants will likely die back with the cold, but you can save seeds for planting next season.

Here are a few 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. Stunted growth and distorted leaves.
• What causes it: Aphids are attracted to stressed plants. In the Desert Southwest, this can be due to extreme heat and inconsistent watering.
• How to fix/prevent it: Nasturtiums are commonly used as a trap crop for aphids. The aphids will attack the nasturtiums instead of your other plants. You can spray the nasturtiums with a strong blast of water from the hose to dislodge the aphids.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green droppings nearby. You might spot small green caterpillars on the plant.
• What causes it: These caterpillars are the larvae of cabbage white butterflies, which are common in the Desert Southwest. They love to munch on leafy greens.
• How to fix/prevent it: Handpick the caterpillars off the plants. You can also use insecticidal soap or Bacillus thuringiensis (Bt) spray, following label instructions carefully.

Black Fly

• What it looks like: Tiny black flies swarming around the plants, especially in the soil. Leaves may turn yellow and wilt.
• What causes it: Black flies thrive in moist conditions. Overwatering or poor drainage can create a breeding ground for them.
• How to fix/prevent it: Improve drainage by amending the soil with compost or perlite. Allow the soil to dry out between waterings. You can also use yellow sticky traps to catch the adult flies.

Desert Southwest Specific Challenges: The extreme heat and intense sunlight can stress nasturtiums, making them more susceptible to pests and diseases. Providing afternoon shade and ensuring consistent watering (without overwatering) are crucial for their survival. Our monsoon season can also lead to fungal issues, so good air circulation is essential.

Nasturtiums are excellent companion plants in the Desert Southwest garden. They attract beneficial insects and can even deter some pests.

Plant nasturtiums near tomatoes, cucumbers, and squash. They act as a trap crop for aphids, drawing them away from your prized veggies. They also help repel squash bugs and cucumber beetles. Nasturtiums also work well with broccoli and cabbage, helping to deter cabbage moths and other pests that target brassicas.

Avoid planting nasturtiums near plants that are particularly susceptible to aphids, as they might attract even more of these pests to your garden overall.