Nasturtium in Zone 9A — Southern California

Nasturtiums are a fantastic addition to any Southern California garden. Their peppery flavor brightens salads, the vibrant flowers add a splash of color to your garden beds, and they're incredibly easy to grow. Plus, they act as a natural trap crop for aphids, drawing them away from your prized veggies.

While we face challenges like drought and occasional heat waves, our long growing season of 322 days gives us plenty of opportunities to enjoy a year-round harvest of these beauties. With a little attention to watering, you'll find Nasturtiums thrive in our climate.

Starting Nasturtiums indoors is possible, but honestly, they do best when direct-sown. However, if you're eager to get a super-early start, you can start seeds indoors from early to late January, about four weeks before you'd like to transplant them outside.

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. Remember to bottom-water your seedlings to encourage strong root growth and prevent damping off. Given our very-early spring character here in SoCal, this indoor start might give you a jump on the season.

Transplant your Nasturtium seedlings outdoors from early February through early March, once the danger of frost has passed. Before planting, harden them off by gradually exposing them to outdoor conditions for about a week.

Choose a sunny spot with well-draining soil, spacing the plants 10-12 inches apart. Keep an eye on the weather forecast; although we rarely get hard freezes, a sudden cold snap could still damage young transplants.

Direct sowing is the way to go with Nasturtiums! You can sow seeds directly into your garden from early February through mid October, taking advantage of our long growing season.

Prepare the soil by loosening it and removing any weeds. Nasturtiums actually prefer poor soil, so don't worry about amending it too much. Sow seeds about ½ inch deep, spacing them 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, which should take about a week or two, depending on soil temperature.

Nasturtiums are drought-tolerant plants that prefer dry conditions, which makes them perfect for water-wise Southern California gardens. Overwatering is a common mistake that leads to lush foliage but fewer flowers.

During our winter-wet season, from late fall through early spring, you likely won't need to water them at all unless we're experiencing a particularly dry spell. In the summer heat inland, when temperatures soar, water deeply about once a week, providing around ½ inch of water. Use the finger test – if the top two inches of soil are dry, it's time to water. Always water at the base of the plant to avoid wetting the foliage, which can encourage fungal diseases in our low-to-moderate humidity.

Yellowing leaves can be a sign of overwatering, while wilting leaves indicate underwatering. Add a layer of mulch around your plants to help retain moisture in the soil and suppress weeds, especially during fire season when water restrictions may be in place.

You can expect your first harvest of Nasturtium flowers and leaves starting in early April and continuing through mid December, thanks to our mild winters. Nasturtiums are ready to harvest about 55 days after sowing.

Harvest the flowers when they are fully open for the best flavor and visual appeal. Simply snip them off the plant with scissors or your fingers. For the leaves, harvest them as needed, choosing younger, more tender leaves. Regular harvesting encourages continued production of both flowers and leaves.

As our first frost approaches around mid- December, you can still harvest any remaining flowers and leaves. You can even let some of the seed pods mature and pickle them for a caper-like treat!

Here are some common problems you might encounter with Nasturtiums in Southern California:

Aphids

• What it looks like: Clusters of small, soft-bodied insects on stems and leaves, often accompanied by sticky honeydew.
• What causes it: Aphids are attracted to stressed plants, and their populations can explode quickly in warm weather. They're common in SoCal due to our mild climate.
• How to fix/prevent it: Nasturtiums are often used intentionally as a trap crop. This means aphids are drawn to them, leaving your other plants alone! If the infestation gets too heavy, blast them off with a strong stream of water from your hose.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green or brown droppings nearby. You might see small green caterpillars munching on the foliage.
• What causes it: These caterpillars are the larvae of cabbage white butterflies, which are common in Southern California gardens.
• How to fix/prevent it: Handpick the caterpillars off the plants and drop them into a bucket of soapy water. You can also cover your plants with row covers to prevent the butterflies from laying their eggs.

Black Fly

• What it looks like: Similar to aphids, these tiny black flies cluster on new growth, sucking sap and weakening the plant.
• What causes it: Black fly thrive in warm, sheltered conditions, and their populations can build up rapidly.
• How to fix/prevent it: Encourage beneficial insects like ladybugs and lacewings, which prey on black fly. A strong blast of water can also dislodge them. Insecticidal soap can be used as a last resort.

Southern California Specific Challenges: Our hot, dry summers can stress Nasturtiums, making them more susceptible to pests. Regular watering (but not overwatering!) and providing some afternoon shade, especially inland, can help keep them healthy. The low-to-moderate humidity generally prevents fungal diseases, but good air circulation is still important.

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

Good companions include tomatoes, cucumbers, and squash. Nasturtiums deter pests that bother these crops. They also do well planted near broccoli and cabbage, acting as a trap crop for cabbage white butterflies, drawing them away from your brassicas.

Avoid planting Nasturtiums near fennel, as they can inhibit each other's growth. Otherwise, Nasturtiums are generally well-behaved and get along with most plants in the garden.