Nasturtium in Zone 7B — Northern California

Nasturtiums are a fantastic addition to any Northern California garden. They offer peppery leaves and vibrant, edible flowers that add a unique flavor to salads and other dishes. Plus, they're incredibly easy to grow in our Mediterranean climate, providing beauty and deliciousness with minimal effort.

While we face challenges like drought and occasional water restrictions, nasturtiums are surprisingly drought-tolerant, making them a perfect fit for water-wise gardening. With our long 245-day growing season, you'll have plenty of time to enjoy these beauties from spring well into fall.

Starting nasturtium seeds indoors is an option, but not usually necessary in our mild Northern California climate. Since we have a long growing season, direct sowing is the preferred method. However, if you want a head start, especially in cooler microclimates, you can start seeds indoors from mid February through early March.

Use seed trays with a good seed-starting mix and keep them in a warm, bright location. Bottom watering is a great way to keep the soil consistently moist without overwatering. Once the seedlings emerge, make sure they get plenty of light to prevent them from becoming leggy before transplanting.

If you started your nasturtiums indoors, transplant them outdoors from late March through mid April, after the last expected frost. Before transplanting, harden off the seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind.

Choose a sunny spot with well-drained soil and space the plants 10-12 inches apart. Keep an eye on the weather forecast. We can still get some unexpected cool snaps and late rains in early spring, so be prepared to cover the seedlings if necessary.

Direct sowing nasturtium seeds is the easiest and most successful method for Northern California gardeners. You can sow seeds directly into the garden from late March through early September. Nasturtiums don't love having their roots disturbed, so direct sowing avoids transplant shock.

Prepare the soil by loosening it and removing any weeds. Nasturtiums actually thrive in slightly poor soil, so there's no need to add extra fertilizer. Sow the seeds about half an inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, which usually takes about a week or two.

Nasturtiums are wonderfully drought-tolerant, making them ideal for our dry Northern California summers. Overwatering is a far bigger concern than underwatering. In fact, they bloom better with less water.

During the spring, when we still get occasional rainfall, you probably won't need to water nasturtiums at all unless we're experiencing a particularly dry spell. Once summer arrives and the temperatures climb, check the soil moisture regularly. Stick your finger about two inches deep into the soil. If it feels dry, it's time to water. Aim for about 1 inch of water per week during the hottest parts of summer. Water at the base of the plants to avoid wetting the foliage, which can lead to fungal problems in some microclimates.

Signs of underwatering include wilting leaves and stunted growth. Overwatering can cause yellowing leaves and root rot. A light layer of mulch, like wood chips or straw, can help retain moisture in the soil and reduce the need for frequent watering, which is a great technique, especially during fire season.

You can expect your first nasturtium harvest about 55 days after planting, typically from mid May through mid November in our long Northern California growing season. Both the flowers and leaves are edible, so harvest them as needed.

Pick the flowers when they are fully open and brightly colored. The leaves can be harvested at any time. For continued production, deadhead the spent flowers regularly. This encourages the plant to produce more blooms. Don't forget about the seed pods! Harvest them when they are still green and plump for a caper-like treat. As the first frost approaches in mid- November, harvest any remaining flowers and seed pods to enjoy before the cold weather arrives.

Even though nasturtiums are easy to grow, they can sometimes encounter a few problems in Northern California gardens:

Aphids:

• What it looks like: Clusters of small, pear-shaped insects (often green, black, or yellow) on stems and leaves. Leaves may be sticky or distorted.
• What causes it: Aphids are attracted to stressed plants. In our dry climate, plants can become stressed from lack of water or inconsistent watering.
• How to fix/prevent it: Nasturtiums are often used as a trap crop for aphids, meaning they attract aphids away from other plants. You can simply tolerate the aphids on the nasturtiums. If the infestation is heavy, spray the plants with a strong stream of water or use insecticidal soap.

Cabbage Caterpillars:

• What it looks like: Holes in leaves, often with green droppings nearby. You might see small green caterpillars munching on the leaves.
• What causes it: Cabbage white butterflies lay their eggs on the leaves, and the caterpillars hatch and start feeding. They can be especially prevalent during our long growing season.
• How to fix/prevent it: Handpick the caterpillars off the plants and drop them into a bucket of soapy water. You can also cover the plants with row covers to prevent the butterflies from laying eggs.

Black Fly:

• What it looks like: Similar to aphids, black flies are small, black insects that cluster on new growth. They suck sap from the plant, causing stunted growth and distorted leaves.
• What causes it: Black flies thrive in warm, dry conditions. Our Mediterranean climate provides ideal conditions for them, especially during the summer.
• How to fix/prevent it: Spray the plants with a strong stream of water to dislodge the black flies. Insecticidal soap or neem oil can also be effective.

Northern California Specific Challenges: Our moderate-to-hot summers, low humidity, and dry-summer rainfall patterns mean that nasturtiums are generally well-suited to our climate. However, be mindful of water stress, which can attract pests. Consistent watering practices and proper soil drainage are key to keeping your nasturtiums healthy and thriving.

Nasturtiums make excellent companion plants for many vegetables in Northern California gardens. They act as a trap crop for aphids, drawing them away from valuable crops like tomatoes, cucumbers, and squash. Plant them nearby to protect these vegetables from aphid infestations.

They also benefit broccoli and cabbage by deterring cabbage white butterflies and other pests. Avoid planting nasturtiums near fennel, as they can inhibit its growth. Also, be mindful of planting them near root vegetables, as their sprawling growth habit can sometimes compete for space and resources.