Nasturtium in Zone 8B — Gulf Coast

Nasturtiums are a fantastic addition to any Gulf Coast garden. Their peppery leaves and vibrant flowers add a unique flavor to salads and a splash of color to your plate. Plus, they attract beneficial insects and can even act as a trap crop for pests, which is a real win given our high humidity and pest pressure.

We know our Gulf Coast climate can be challenging, with its long, hot, humid summers and the ever-present threat of afternoon storms. But with a little planning, you can easily grow nasturtiums during our long growing season (about 284 days!). The key is to time your planting right to avoid the worst of the summer heat and humidity.

Starting nasturtiums indoors is possible, but honestly, they do best when direct sown. They don’t love being transplanted, so I only recommend starting them indoors if you're trying to get a very early start.

If you do start indoors, begin in late January through mid February, about four weeks before the last average frost date. Use seed trays with good drainage and a well-draining seed starting mix. Keep the trays warm and provide plenty of light, either from a sunny window or a grow light. Remember to water from the bottom to prevent damping off, which can be a problem in our humid climate.

If you started your nasturtiums indoors, transplant them outdoors in late February through late March. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

When transplanting, space them about 10-12 inches apart. Keep an eye on the weather; we can still get some cool snaps during this time, so be prepared to cover them if temperatures dip unexpectedly.

Direct sowing is the way to go with nasturtiums! Wait until after the last average frost date and direct sow in late February through late September.

Choose a spot with full sun to part shade and prepare the soil by loosening it and removing any weeds. Nasturtiums aren’t picky about soil, in fact, they thrive in poor soil. Sow seeds about ½ inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, usually in about a week or two.

Nasturtiums are pretty drought-tolerant once established, which is a good thing since we often get periods of dry weather even with our high annual rainfall. The trick is to find the right balance, especially with our high humidity.

During the spring and fall, when temperatures are milder, water only when the top 2 inches of soil feel dry to the touch. Stick your finger in there – that's the best way to tell! Usually, about ½ inch of water per week is plenty, but let the rainfall be your guide. In the heat of summer, you might need to water more frequently, but be careful not to overwater.

Always water at the base of the plant to avoid wetting the leaves, which can encourage fungal diseases in our humid climate. Signs of underwatering include wilting leaves and dry soil. Overwatering can lead to yellowing leaves and root rot. A light layer of mulch around the base of the plants can help retain moisture and suppress weeds, but don’t overdo it, you want good airflow.

You can expect your first harvest of nasturtium flowers and leaves in late April through early December, about 55 days after planting.

Harvest the flowers when they are fully open for the best flavor and visual appeal. Snip them off with scissors or pinch them off with your fingers. The leaves can be harvested at any time. Just be sure to leave enough foliage for the plant to continue growing. The seed pods are also edible when green and can be pickled like capers.

To encourage continued production, harvest regularly. As the first frost approaches in early December, harvest any remaining flowers and leaves. You can even let some of the seed pods dry on the plant and save them for next year's planting.

Here are some common issues we see with nasturtiums in the Gulf Coast:

Aphids

• What it looks like: Small, pear-shaped insects clustered on stems and leaves, often accompanied by sticky honeydew and sooty mold.
• What causes it: Aphids are attracted to stressed plants, and our warm, humid conditions can sometimes weaken plants.
• How to fix/prevent it: Nasturtiums are often used as a trap crop for aphids, drawing them away from other plants. You can also spray them off with a strong blast of water from the hose. Insecticidal soap can also be effective.

Cabbage Caterpillars

• What it looks like: Green caterpillars that chew holes in leaves, leaving behind droppings.
• What causes it: Cabbage white butterflies lay their eggs on the underside of leaves, and the caterpillars hatch and start feeding.
• How to fix/prevent it: Handpick the caterpillars off the plants and dispose of them. You can also use Bacillus thuringiensis (Bt), a natural insecticide that is safe for humans and pets.

Black Fly

• What it looks like: Small, black flies that swarm around plants, especially new growth.
• What causes it: These flies thrive in moist conditions and feed on plant sap.
• How to fix/prevent it: Improve air circulation around the plants and avoid overwatering. Insecticidal soap can also be used to control infestations.

Gulf Coast Specific Challenges: Our hot, humid climate and wet-year-round rainfall create the perfect environment for fungal diseases and pests. Be sure to provide good air circulation around your nasturtiums and avoid overwatering to minimize these problems. Keep a close eye on your plants and address any issues promptly to prevent them from spreading.

Nasturtiums make great companions for several plants in the Gulf Coast garden. They attract beneficial insects that can help pollinate tomatoes, cucumbers, and squash, leading to better yields. They also deter pests like squash bugs and cabbage moths from broccoli and cabbage.

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