Nasturtium in Zone 8A — Northern California

Nasturtiums are a fantastic addition to any Northern California garden. Their peppery leaves and vibrant flowers brighten salads, and the entire plant is edible! Plus, they thrive in our Mediterranean climate, adding beauty and flavor to your garden from spring through fall.

While we NorCal gardeners face challenges like drought and water restrictions, nasturtiums are surprisingly low-maintenance. With our long 255-day growing season, you'll have plenty of time to enjoy these beauties. The key is understanding the timing, and we'll cover that.

Starting nasturtiums indoors is possible, but honestly, it's often not necessary in our mild Northern California climate. If you're eager to get a super early start, you can begin indoors from early February through early March, about four weeks before you plan to transplant.

Use seed trays with good drainage and a well-draining potting mix. Keep them in a warm spot with plenty of light; a sunny windowsill or grow lights work well. Bottom watering helps prevent damping-off. With our early springs here, you might find direct sowing is just as effective.

If you started your nasturtiums indoors, aim to transplant them outdoors from mid March through mid April. Before transplanting, harden them off by gradually exposing them to outdoor conditions for about a week.

Space the seedlings 10-12 inches apart. Keep an eye on the weather forecast – a late cold snap can happen, even here. If frost is predicted, cover your young plants.

Direct sowing is the preferred method for nasturtiums, and it's easy in Northern California! You can sow seeds directly into the garden from mid March through mid September.

Choose a sunny to partly shaded spot with well-drained soil. Nasturtiums aren't picky and actually prefer poorer soil. Make sure the soil has warmed up a bit. Sow seeds 1/2 inch deep and 10-12 inches apart. Keep the soil consistently moist until germination, which usually takes about a week or two.

Nasturtiums are quite drought-tolerant, making them ideal for our dry Northern California summers. The trick is to avoid overwatering, which can lead to more foliage than flowers.

During the cooler spring and fall months, water only when the top two inches of soil feel dry to the touch – use the finger test! In the heat of summer, you might need to water once or twice a week, giving them about ½ inch of water each time. Water at the base of the plant to avoid wetting the foliage.

Yellowing leaves can indicate overwatering, while wilting leaves signal underwatering. A light layer of mulch can help retain soil moisture, especially during our hotter months, but avoid heavy mulching which can keep the soil too wet.

Your first nasturtium harvest will likely be from mid May through mid November, about 55 days after planting. The flowers are ready to pick when fully open, offering the most intense flavor. The leaves can be harvested at any time.

Gently snip off the flowers or leaves with scissors or your fingers, being careful not to damage the plant. Regular harvesting encourages more blooms. As our first frosts approach in mid- November, harvest any remaining flowers and leaves. You can even pickle the green seed pods for a caper-like treat.

Here are three common problems you might encounter with nasturtiums in Northern California:

Aphids

• What it looks like: Clusters of small, pear-shaped insects on stems and undersides of leaves; sticky residue (honeydew).
• What causes it: Aphids are attracted to lush growth, which can be triggered by too much fertilizer or water. Our moderate-to-hot summer days can also stress plants, making them more susceptible.
• How to fix/prevent it: Nasturtiums are often used as a trap crop to lure aphids away from other plants. Blast them off with a strong stream of water from the hose. Introduce beneficial insects like ladybugs.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green or brown droppings nearby. You might spot the caterpillars themselves, which are usually green and blend in well.
• What causes it: Cabbage white butterflies lay their eggs on nasturtiums, and the caterpillars hatch and start munching. The caterpillars thrive in our long growing season.
• How to fix/prevent it: Handpick caterpillars off the plants. Cover plants with row covers to prevent butterflies from laying eggs.

Black Fly

• What it looks like: Similar to aphids, these small black flies suck sap from leaves, causing them to wilt and distort.
• What causes it: Like aphids, they are attracted to stressed plants and can multiply quickly in warm weather.
• How to fix/prevent it: Blast them off with water. Insecticidal soap can also be effective. Ensure good air circulation around plants.

Northern California Specific Challenges: Our dry summers can stress nasturtiums, making them more vulnerable to pests. Consistent monitoring and prompt action are key. Avoid overwatering, even during hot spells.

Nasturtiums are excellent companion plants in Northern California gardens. They attract beneficial insects and can deter pests.

Tomatoes, cucumbers, and squash benefit from nasturtiums because the flowers attract pollinators and the plant can act as a trap crop for aphids. Broccoli and cabbage also benefit, as nasturtiums can deter cabbage white butterflies. Avoid planting nasturtiums near fennel, as they can inhibit each other's growth.