Nasturtium in Zone 7A — Northern California

Nasturtiums are a fantastic addition to any Northern California garden. Their peppery leaves and vibrant edible flowers add a unique zest to salads and other dishes. Plus, they're incredibly easy to grow and thrive in our Mediterranean climate, providing beauty and flavor throughout our long growing season.

While we face challenges like drought and increasingly intense fire seasons here in NorCal, nasturtiums are surprisingly resilient. With a growing season that stretches roughly from mid-March to early November, you'll have plenty of time to enjoy these beauties.

Starting nasturtiums indoors isn't essential, given our long growing season, but it can give you a head start. If you're eager to see those first blooms extra early, sow seeds indoors from mid-February through mid-March, roughly four weeks before you plan to transplant.

Use seed trays with a well-draining seed starting mix. Keep them in a warm spot, ideally around 70°F, and provide ample light – a sunny windowsill or grow lights work well. Bottom watering is key to prevent damping off; set the tray in a shallow dish of water and let the soil absorb the moisture from the bottom. With our early spring warmth, indoor starts need to be monitored closely to prevent them from getting leggy.

Transplant your nasturtium seedlings outdoors from late March through late April, after the last expected frost. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun and wind, preventing transplant shock.

Space plants about 10-12 inches apart in a sunny spot with well-draining soil. Be mindful of potential late frosts that sometimes surprise us in early spring; have frost cloth ready to protect your young plants if needed.

Direct sowing is the preferred method for nasturtiums, as they don't always love having their roots disturbed. Sow seeds directly into the garden from late March through early September, ensuring the soil has warmed up a bit.

Choose a spot with full sun to partial shade and prepare the soil by loosening it and removing any weeds. Plant seeds about ½ inch deep and 10-12 inches apart. Keep the soil consistently moist until the seedlings emerge, usually within a week or two. Remember, nasturtiums thrive in slightly poor soil, so no need to amend with fertilizer.

Nasturtiums are wonderfully drought-tolerant, making them perfect for our water-wise gardens in Northern California. They actually prefer drier conditions, so less is definitely more when it comes to watering. Overwatering can lead to lush foliage but fewer flowers.

During our dry summers, water deeply but infrequently. A good rule of thumb is to check the soil about 2 inches deep – if it's dry, it's time to water. Aim for about 1 inch of water per week, especially during the hottest periods. Water at the base of the plants to avoid wetting the leaves, as our low humidity generally keeps fungal issues at bay.

Yellowing leaves can indicate overwatering, while wilting leaves suggest underwatering. Adjust your watering schedule accordingly. Adding a layer of mulch around your plants helps retain moisture in the soil and reduces the need for frequent watering – wood chips or straw work great.

You can expect your first nasturtium harvest from late May through early November, about 55 days after planting. The flowers are ready to harvest when they are fully open and vibrant in color. Both the leaves and flowers have a peppery taste, so harvest them as needed for your culinary creations.

To harvest, simply snip the flowers or leaves from the plant with scissors or your fingers. Regular harvesting encourages continued production of both flowers and leaves. Even the seed pods can be harvested and pickled, offering a caper-like flavor.

As we approach the first frost in early November, harvest any remaining flowers and seed pods. While nasturtiums are tender and won't survive a frost, you can collect the seeds to plant again next year, ensuring another season of beauty and flavor in your garden.

Here are a few common issues to watch out for with nasturtiums in Northern California:

Aphids

• What it looks like: Clusters of small, soft-bodied insects on stems and leaves, often accompanied by sticky honeydew and sooty mold.
• What causes it: Aphids are attracted to stressed plants, and their populations can explode quickly in warm, dry conditions typical of our summers.
• 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. Introduce beneficial insects like ladybugs or lacewings.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green droppings nearby. You might spot the caterpillars themselves, which are green and blend in well with the foliage.
• What causes it: Cabbage white butterflies lay their eggs on nasturtiums, and the caterpillars hatch and start feeding.
• How to fix/prevent it: Handpick caterpillars off the plants. Cover plants with row covers to prevent butterflies from laying eggs. Bacillus thuringiensis (Bt) is an effective organic control option.

Black Fly

• What it looks like: Similar to aphids, these small black flies cluster on stems and new growth, sucking sap and weakening the plant.
• What causes it: Black fly thrive in sheltered locations with poor air circulation, which can sometimes occur even with our breezes.
• How to fix/prevent it: Improve air circulation by thinning out crowded plants. Spray plants with insecticidal soap or neem oil. Encourage beneficial insects like hoverflies, which prey on black fly.

Northern California Specific Challenges: Our moderate-to-hot, dry summers can stress nasturtiums if they aren't watered properly. Monitoring soil moisture and providing adequate but not excessive water is key. The low humidity generally helps prevent fungal diseases, but be vigilant for pests that thrive in dry conditions.

Nasturtiums make excellent companions for several plants in your Northern California garden. They attract aphids, acting as a trap crop to protect tomatoes, cucumbers, and squash from these pests. They also deter cabbage white butterflies, benefiting broccoli and cabbage.

Avoid planting nasturtiums near fennel, as they can inhibit each other's growth. Otherwise, nasturtiums are relatively easygoing and get along well with most other garden vegetables and herbs.