Nasturtium in Zone 8B — Southeast

Nasturtiums are worth their weight in gold here in the Southeast. They're not only beautiful, but the peppery flavor of the leaves and flowers adds a delicious kick to salads. Plus, they practically thrive in our long summer, offering a vibrant splash of color when other flowers are fading in the heat.

We definitely have our share of gardening challenges with the humidity and clay soil, but nasturtiums are surprisingly resilient. With our extended 255-day growing season, you'll have plenty of time to enjoy these beauties, even if you get a late start.

Starting nasturtiums indoors is doable, but honestly, these plants prefer to be direct-sown. However, if you're itching to get a head start, you can sow seeds indoors from early February through early March, about four weeks before our typical transplant window.

Use seed trays with a good seed-starting mix, and keep them warm and well-lit – a sunny windowsill or grow lights work great. Water from the bottom to encourage strong root growth and prevent damping-off, which can be a problem with our moderate spring humidity. Just set the tray in a shallow dish of water until the top of the soil is moist.

Transplanting nasturtiums outdoors should be done from mid March through mid April, after the last threat of frost has passed. Before you move them outside permanently, harden them off by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sunlight and temperature swings.

Plant them 10-12 inches apart in well-draining soil. Keep an eye on the weather forecast around transplant time. A late cold snap can set them back, so be prepared to cover them if necessary.

Direct sowing is the way to go with nasturtiums here in the Southeast. They don't love having their roots disturbed, and direct sowing avoids that issue altogether. You can sow seeds from mid March all the way through mid September.

Just make sure the soil is warm, ideally around 60-70°F. Plant the seeds about half an inch deep and 10-12 inches apart. Nasturtiums aren't picky about soil, so don't worry too much about amending our clay soil. In fact, they often do better in slightly poor soil!

Nasturtiums are remarkably drought-tolerant and actually prefer slightly dry conditions, which is good news for us Southeast gardeners dealing with hot, humid summers. Overwatering is a bigger problem than underwatering with these plants.

During the spring and fall, when temperatures are milder and we get more consistent rainfall, you may not need to water them at all unless we're experiencing a dry spell. In the heat of summer, check the soil moisture regularly using the "finger test." Stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Aim for about an inch of water per week, either from rainfall or irrigation.

Water at the base of the plants rather than overhead to minimize humidity around the leaves, which can help prevent fungal diseases. Yellowing leaves can indicate overwatering, while wilting leaves suggest they need a drink. Adding a layer of pine straw mulch around the base of the plants can help retain moisture and suppress weeds, but be careful not to over-mulch, as this can contribute to excessive moisture.

Here in the Southeast, you can expect your first nasturtium harvest from mid May through mid November, about 55 days after sowing. The flowers are ready to pick when they're fully open and vibrantly colored. The leaves can be harvested at any time.

To harvest, simply snip the flowers or leaves with scissors or your fingers, being careful not to damage the rest of the plant. Regular harvesting encourages more flower production, so don't be shy! Even as our first frost approaches in mid- November, you can often extend the harvest by covering the plants on chilly nights.

Nasturtiums are generally easy to grow, but here are a few common problems we see in the Southeast:

Aphids

• What it looks like: Clusters of small, soft-bodied insects on stems and leaves, often accompanied by sticky honeydew.
• What causes it: Aphids thrive in warm, humid conditions, and our Southeast summers provide the perfect environment for them.
• How to fix/prevent it: Nasturtiums are often used as a trap crop for aphids, drawing them away from other plants. Blast them off with a strong stream of water from the hose. Insecticidal soap can also be effective.

Cabbage Caterpillars

• What it looks like: Holes in the leaves, often with green droppings nearby. You might spot the caterpillars themselves, which are usually green and blend in with the foliage.
• What causes it: These caterpillars are the larvae of cabbage white butterflies, which are common in the Southeast.
• How to fix/prevent it: Handpick the caterpillars off the plants. Bacillus thuringiensis (Bt) is a biological insecticide that's effective against caterpillars.

Black Fly

• What it looks like: Tiny black flies swarming around the plants, especially in new growth.
• What causes it: High humidity and poor air circulation can contribute to black fly infestations.
• How to fix/prevent it: Improve air circulation by spacing plants properly. Insecticidal soap can help control infestations.

Southeast Specific Challenges: Our hot, humid climate means that fungal diseases can be a problem for nasturtiums. Ensure good air circulation, avoid overhead watering, and consider using a copper fungicide if necessary. Japanese beetles can also be a nuisance, munching on the leaves and flowers. Handpicking them or using traps can help keep them under control.

Nasturtiums are great companions for many plants in the Southeast garden. They attract beneficial insects and can even deter some pests.

Good companions include tomatoes, cucumbers, and squash. Nasturtiums help repel aphids and squash bugs, protecting these crops. They also do well planted near broccoli and cabbage, helping to deter cabbage moths. Avoid planting them near fennel, as it can inhibit their growth.