Nasturtium in Zone 6B — Pacific Northwest

Nasturtiums are a fantastic addition to any Pacific Northwest garden. Their peppery leaves and bright, edible flowers add a unique zing to salads and a splash of color to your garden beds. Plus, they're incredibly easy to grow here, thriving in our mild summers and even tolerating our cool nights.

While our springs can be slow to warm up and our summers aren't scorching, nasturtiums are adaptable enough to flourish with a little attention to timing. Our 162-day growing season provides ample opportunity to enjoy these beauties from summer through fall.

Starting nasturtiums indoors is possible, but not usually necessary in our climate. Given our mild summers, direct sowing is generally more successful since nasturtiums don't love being transplanted. However, if you're eager to get a head start, you can start seeds indoors from early to late April, about four weeks before our typical last frost date.

Use seed trays with well-draining potting mix and provide warmth and bright light, ideally a grow light, as our overcast spring days can be dim. Bottom watering will help prevent damping off, which can be a problem with cool spring temperatures.

If you started your nasturtiums indoors, transplant them outdoors from early May through early June, after the danger of frost has passed. Before transplanting, harden off your seedlings by gradually exposing them to outdoor conditions for about a week. This helps them adjust to the cooler temperatures and stronger sunlight.

Space your nasturtiums 10-12 inches apart. Keep an eye on the weather forecast; a late cold snap can still occur, so be prepared to cover your seedlings if needed.

Direct sowing is the easiest and most successful way to grow nasturtiums in the Pacific Northwest. Sow seeds directly into the garden from early May through early August. Nasturtiums resent transplanting, so this method minimizes stress on the plants.

Choose a sunny spot with well-drained soil. While nasturtiums aren't picky, avoid overly rich soil as it encourages leaf growth over flowering. Simply press the seeds about ½ inch deep and 10-12 inches apart, then water gently. Keep the soil consistently moist until seedlings emerge, which usually takes about a week or two.

Nasturtiums are drought-tolerant and thrive on neglect, making them perfect for our dry summer months in the Pacific Northwest. Overwatering is a far greater concern than underwatering with these plants. During our wet springs, you likely won't need to water them at all.

Once the dry summer months arrive, check the soil moisture by sticking your finger about 2 inches deep. If the soil feels dry, give them a good watering, aiming for about 1 inch of water per week, especially during hotter spells, which are still rarely above 90°F here. Water at the base of the plants to avoid wetting the foliage, which can encourage fungal diseases, although our dry summers usually keep that in check.

Yellowing leaves can indicate overwatering, while wilting leaves signal underwatering. A light layer of mulch, such as straw or wood chips, can help retain moisture in the soil during the driest periods, but avoid heavy mulching, which can lead to overly moist conditions.

You can expect your first harvest of nasturtium flowers and leaves from early July through early October, roughly 55 days after sowing. The flowers are ready to harvest when they're fully open and brightly colored. The leaves can be harvested at any time.

To harvest, simply snip off the flowers or leaves with scissors or your fingers, being careful not to damage the plant. Regular harvesting encourages continued production. As the first frost approaches in early October, harvest any remaining flowers and seed pods. The seed pods can be pickled for a caper-like treat.

Here are three common problems you might encounter with nasturtiums in the Pacific Northwest:

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 can thrive in warm, dry conditions. They don't love the PNW, but can be an issue.
• How to fix/prevent it: Nasturtiums often act as a trap crop for aphids, drawing them away from other plants. You can also blast aphids off with a strong stream of water or introduce beneficial insects like ladybugs.

Cabbage Caterpillars

• What it looks like: Holes in leaves, often with green droppings nearby. You might also spot the caterpillars themselves, which are usually green and blend in 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 or cover your nasturtiums with netting to prevent butterflies from laying eggs.

Black Fly

• What it looks like: Similar to aphids, but black in color. They cluster on new growth and suck plant sap.
• What causes it: Similar to aphids, they prefer stressed plants and can quickly multiply.
• How to fix/prevent it: Treat the same way as aphids – strong water spray, introduce beneficial insects, or use insecticidal soap as a last resort.

Pacific Northwest Specific Challenges: Our mild heat and dry-summer humidity generally benefit nasturtiums, as they don't like excessive heat or moisture. However, cool soil in spring can slow germination, so be patient when direct sowing. Late blight is not a direct issue for nasturtiums, but it's a good reminder to maintain good air circulation to prevent fungal diseases in other plants. Slugs are always a concern in our region, so use slug bait or other control methods if they become a problem.

Nasturtiums make excellent companion plants for many vegetables in the Pacific Northwest. They attract beneficial insects and can deter pests.

Good companions include tomatoes, cucumbers, and squash, as nasturtiums help repel aphids and other pests that can damage these crops. They also work well with broccoli and cabbage, deterring cabbage white butterflies. Avoid planting nasturtiums near fennel, as they can inhibit each other's growth.