Nasturtium in Zone 6A — Pacific Northwest

Nasturtiums are a delight in the Pacific Northwest garden. Their peppery leaves and bright flowers add a zesty kick to salads, and the entire plant is edible. Plus, they're incredibly easy to grow here, rewarding even the most novice gardener with a splash of color and flavor throughout our mild summers and into the extended fall.

While we might struggle with heat-loving plants, Nasturtiums thrive in our cooler conditions. Our 148-day growing season gives you plenty of time to enjoy them. Don't worry about our wet springs or the occasional late blight warnings; with proper timing, Nasturtiums are a breeze.

Starting Nasturtiums indoors is possible, but generally not necessary here in the PNW. Because they resent transplanting, direct sowing is the preferred method. Still, if you're eager to get a head start or want to ensure blooms as early as possible, starting seeds indoors from mid-April through early May is an option.

Use seed trays with well-draining soil, and keep them in a warm spot with plenty of light. Bottom watering is a great way to keep the soil consistently moist without disturbing the delicate seedlings. Be prepared for a slow start, as overcast spring days can delay germination.

If you've started your Nasturtiums indoors, aim to transplant them outdoors from mid-May through mid-June. Before planting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the sun, wind, and temperature fluctuations.

Space your Nasturtiums 10-12 inches apart in a sunny or partially shaded spot. Keep an eye on the weather forecast, as late frosts can still occur during this time. Protect your young plants with row covers if a frost is predicted.

Direct sowing is the easiest and most successful way to grow Nasturtiums in the Pacific Northwest. Wait until after the last expected frost, usually around mid-May, before sowing your seeds. You can continue sowing seeds through late July for a continuous harvest.

Prepare the soil by loosening it and removing any weeds. Nasturtiums aren't picky about soil, and actually prefer poor soil that isn't too rich. Sow seeds 1/2 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 remarkably drought-tolerant and thrive in the dry summer months of the Pacific Northwest. Overwatering is a far bigger concern than underwatering. In fact, too much water or fertilizer can lead to lush foliage at the expense of those beautiful, edible flowers.

During our wet springs, you likely won't need to water at all. Once the dry summer months arrive, check the soil moisture regularly. Stick your finger about 2 inches deep into the soil; if it feels dry, it's time to water. Usually, about an inch of water per week is sufficient. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases in our occasionally humid conditions.

Wilting leaves are a sign of underwatering, while yellowing leaves can indicate overwatering. Mulching around the base of the plants with straw or wood chips can help retain soil moisture and suppress weeds, further reducing the need for frequent watering.

You can expect your first Nasturtium harvest from mid-July through early October, about 55 days after planting. Both the flowers and leaves are edible and have a peppery flavor. Harvest the flowers when they are fully open for the best taste and appearance.

To harvest, simply snip the stems of the flowers or leaves with scissors or your fingers. Regular harvesting encourages continued production throughout the season. The seed pods are also edible when green and can be pickled as a caper substitute.

As the first frost approaches in early October, harvest any remaining flowers and seed pods. Even after a light frost, the leaves may still be usable, though their flavor might be slightly affected.

Here are a few common problems you might encounter with Nasturtiums in the Pacific Northwest:

Aphids

• What it looks like: Clusters of tiny green, black, or brown insects on stems and undersides of leaves. Leaves may be sticky or distorted.
• What causes it: Aphids are attracted to new growth and can multiply quickly in warm weather. Our mild summers provide ample opportunity for them to thrive.
• How to fix/prevent it: Nasturtiums are often used as a trap crop to lure aphids away from other plants. You can also blast aphids off with a strong stream of water from the hose. Encourage beneficial insects like ladybugs and lacewings, which prey on aphids.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green droppings nearby. You might also spot the caterpillars themselves, which are green and blend in with the foliage.
• What causes it: Cabbage white butterflies lay their eggs on Nasturtium leaves, and the resulting caterpillars feed on the plant. The PNW's long growing season allows for multiple generations of these pests.
• How to fix/prevent it: Handpick caterpillars off the plants and drop them into a bucket of soapy water. Cover your plants with netting to prevent butterflies from laying eggs.

Black Fly

• What it looks like: Similar to aphids, black flies are small, black insects that cluster on stems and leaves, sucking plant juices. Leaves may become distorted or yellowed.
• What causes it: Black flies are attracted to stressed plants and can become a problem during periods of drought or poor soil conditions.
• How to fix/prevent it: Ensure your plants have adequate moisture and nutrients. A strong blast of water from the hose can dislodge black flies. Insecticidal soap can also be used, but be careful not to harm beneficial insects.

Pacific Northwest Specific Challenges: Our mild heat and dry summer rainfall can actually benefit Nasturtiums, reducing the risk of fungal diseases that thrive in humid conditions. However, the cool soil in spring can slow germination, so be patient when direct sowing.

Nasturtiums are excellent companion plants for several vegetables in the Pacific Northwest garden. They attract aphids, drawing them away from your more valuable crops like tomatoes, cucumbers, and squash. They also deter cabbage moths, protecting broccoli and cabbage.

Avoid planting Nasturtiums near fennel, as they can compete for resources. Otherwise, Nasturtiums are generally beneficial companions that add beauty and pest control to your garden.