Nasturtium in Zone 10A — Desert Southwest

Nasturtiums are a fantastic addition to any Desert Southwest garden. Their peppery leaves and vibrant flowers add a unique zest to salads and other dishes. Plus, they’re incredibly versatile and rewarding to grow, even in our challenging climate.

While our extreme heat and alkaline soil present unique hurdles, Nasturtiums thrive with proper timing and care. With our long 339-day growing season, you have ample opportunity to enjoy these beauties.

Starting Nasturtiums indoors is possible, but not usually necessary in our climate. Since we can direct sow almost year-round, it's often easier to skip this step. However, if you want a head start, begin in late December through mid January, about four weeks before our typical last frost.

Use seed trays with well-draining potting mix. Keep them warm and provide plenty of light – a grow light is helpful. Water from the bottom to encourage strong root growth and prevent damping off. Remember, with our very-early spring character, you'll need to keep an eye on the weather and be ready to transplant as soon as conditions allow.

Transplant your Nasturtium seedlings outdoors in late January through late February. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week. This prevents shock.

Space them 10-12 inches apart in well-draining soil. Keep an eye on overnight temperatures, as a late cold snap can still occur. Protect your young plants with frost cloth if needed.

Direct sowing is the preferred method for Nasturtiums in our region, as they resent transplanting. Sow seeds directly into the ground from late January through mid October. This gives you two potential growing seasons!

Choose a sunny spot with well-draining soil. Nasturtiums aren't picky, but avoid overly rich soil, which can lead to more leaves than flowers. Plant seeds about ½ inch deep and space them 10-12 inches apart. Keep the soil consistently moist until germination, which usually takes about a week.

Watering is crucial, especially during our scorching summers. While Nasturtiums are drought-tolerant once established, consistent moisture is key during their early growth. After that, less is more.

During our spring and fall growing seasons, water deeply about once a week, providing about ½ inch of water. In the extreme summer heat, increase this to twice a week, but always check the soil first. Stick your finger about 2 inches deep – if it's dry, it's time to water. With arid humidity, watering at the base of the plant is best to avoid fungal issues.

Yellowing leaves can indicate overwatering, while wilting signals underwatering. Add a layer of organic mulch around your plants to help retain moisture and regulate soil temperature. This is especially important for summer survival.

You can expect your first harvest of Nasturtium flowers and leaves in late March through late December, about 55 days after planting. Both the flowers and leaves are edible, offering a peppery bite.

Harvest flowers when they are fully open for the best flavor and visual appeal. Use scissors or pinch them off gently to avoid damaging the plant. Regular harvesting encourages continued production. Even the seed pods can be harvested and pickled for a caper-like treat!

As our first frost approaches in late December, harvest any remaining flowers and leaves. The plants will likely die back, but you can collect the seeds to sow again next year.

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

Aphids

• What it looks like: Clusters of tiny green, black, or brown insects on stems and leaves, often causing distorted or yellowing foliage.
• What causes it: Aphids are attracted to stressed plants, and our extreme heat and water scarcity can weaken Nasturtiums, making them vulnerable. Also, they're just part of desert gardening.
• How to fix/prevent it: Nasturtiums are sometimes used as a trap crop, intentionally attracting aphids away from other plants. If infestations get out of control, spray with a strong blast of water or use insecticidal soap.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often accompanied by green droppings. You might also see small green caterpillars munching on the foliage.
• What causes it: These caterpillars are the larvae of cabbage white butterflies, which are common in our region.
• How to fix/prevent it: Handpick caterpillars off plants or use Bacillus thuringiensis (Bt), a biological insecticide.

Black Fly

• What it looks like: Similar to aphids, these small black flies suck sap from the plant, weakening it.
• What causes it: These pests thrive in warm conditions and can quickly multiply in our climate.
• How to fix/prevent it: Insecticidal soap or neem oil can help control black fly infestations.

Desert Southwest Specific Challenges: Our extreme heat can stress Nasturtiums, making them more susceptible to pests and diseases. Providing adequate shade during the hottest part of the day and ensuring consistent watering (without overwatering) are crucial for their survival. Also, our alkaline soil can sometimes affect nutrient uptake, so consider amending with compost to improve soil health.

Nasturtiums make excellent companions for several plants in the Desert Southwest garden. They attract pollinators and can even deter certain pests.

Good companions include tomatoes, cucumbers, and squash. Nasturtiums help repel aphids and other pests that can plague these crops. They also work well with broccoli and cabbage, attracting beneficial insects that prey on cabbage worms. Avoid planting them near fennel, as it can inhibit their growth.