Washington’s coastal climate and cooler springs make waiting until late May or early June the safest bet for direct-sowing nasturtium seeds. Knowing the best time to plant nasturtium in washington is key to getting those bright, edible flowers all summer long. If you sow too early, cold soil and spring rains can rot the seeds or kill tender seedlings.
Nasturtiums are surprisingly fussy about cold. They hate frost and struggle in soil that stays below 55°F. In Washington, from the Puget Sound lowlands to the eastern plains, the window for planting shifts by a few weeks. This guide gives you exact timing for every region, plus tips for starting indoors and caring for your plants.
Best Time To Plant Nasturtium In Washington
The exact date depends on your local microclimate. Western Washington, with its mild but wet springs, needs a later start than the hotter, drier east side. The safest rule is to wait until all danger of frost has passed and the soil has warmed to at least 60°F. For most of the state, that means late May through mid-June.
Western Washington (Coastal And Lowland Areas)
In Seattle, Tacoma, Olympia, and the coastal regions, spring is cool and damp. Soil warms slowly. Direct-sow seeds outdoors between May 25 and June 10. If you want earlier blooms, start seeds indoors 4-6 weeks before your last frost date (typically mid-April).
- Last frost date: Usually April 15-30
- Soil temperature target: 60°F consistently
- Best direct-sow window: Late May to early June
- Indoor start date: Mid-March to early April
Eastern Washington (Inland And Higher Elevations)
Spokane, Yakima, and the Columbia Basin have hotter summers but later frosts. Spring comes faster here, but cold snaps can happen into May. Direct-sow from May 15 to June 1. Soil warms quicker, so you can plant a bit earlier than the west side.
- Last frost date: Usually May 1-15
- Soil temperature target: 60°F
- Best direct-sow window: Mid-May to early June
- Indoor start date: Late March to mid-April
Mountain And High-Elevation Areas
If you live in the Cascades or near Mount Rainier, your growing season is short. Wait until June 1-15 for direct sowing. Even then, be ready to cover plants if a late frost threatens. Starting indoors is strongly recommended for these areas.
- Last frost date: May 15 to June 1
- Soil temperature target: 60°F
- Best direct-sow window: June 1-15
- Indoor start date: Early to mid-April
Why Timing Matters So Much
Nasturtiums are not frost-hardy. A single night below 32°F will kill seedlings. Cold, wet soil also encourages damping off, a fungal disease that rots stems at the soil line. Waiting for warm soil gives you stronger plants that bloom longer.
If you plant too late, you risk missing the peak summer bloom. Nasturtiums slow down in extreme heat (above 90°F). In Washington, that’s rarely a problem, but eastern areas can hit those temps in July. Planting in late May or early June gives plants time to establish before the heat arrives.
Soil Temperature Is The Real Key
Air temperature is misleading. Soil warms much slower. Use a soil thermometer to check. Insert it 2-3 inches deep in the morning. If it reads 60°F or higher for three consecutive days, it’s safe to sow. In Washington, this often happens 2-3 weeks after the last frost.
- Buy a soil thermometer (under $10 at garden centers)
- Check soil temperature daily in late May
- Wait for three days of 60°F or above
- Then sow seeds directly outdoors
How To Start Nasturtium Seeds Indoors
Starting indoors gives you a 4-6 week head start. This is especially useful in cooler parts of Washington. Use biodegradable pots because nasturtiums dislike root disturbance. Peat pots or paper cups work well.
Step-By-Step Indoor Sowing
- Fill pots with seed-starting mix
- Plant seeds 1/2 inch deep
- Water gently and cover with plastic wrap
- Place in a warm spot (65-70°F)
- Seeds germinate in 7-14 days
- Remove plastic once sprouts appear
- Provide bright light (a sunny window or grow light)
- Harden off seedlings for 7 days before transplanting
Hardening off is critical. Gradually expose seedlings to outdoor conditions over a week. Start with 1 hour in shade, then increase daily. This prevents shock and sunburn.
Transplanting Outdoors
Wait until soil is warm and nights stay above 50°F. Space plants 10-12 inches apart. Water well after transplanting. If a cold snap is forecast, cover with row cover or a cloche overnight.
Direct Sowing Nasturtiums In Washington Soil
Direct sowing is easier and often produces sturdier plants. Nasturtiums have taproots that don’t like being moved. If you have warm soil and patience, direct sow.
Preparing The Bed
Nasturtiums prefer poor to average soil. Too much nitrogen makes leaves lush but flowers few. Skip fertilizer. Just loosen the soil to 6 inches deep and remove weeds.
- Choose a sunny spot (6+ hours of direct sun)
- Well-draining soil is essential
- Add compost only if soil is very sandy or heavy clay
- Rake smooth before sowing
Sowing Technique
- Soak seeds in water overnight to soften the hard coat
- Plant 2 seeds per hole, 1/2 inch deep
- Space holes 10-12 inches apart
- Cover with soil and water gently
- Thin to the strongest seedling after emergence
Soaking seeds is optional but helps germination in cool soil. If you skip it, expect germination in 10-14 days instead of 7-10.
Caring For Nasturtiums Through Washington’s Summer
Once established, nasturtiums are low-maintenance. They thrive on neglect. Overwatering and overfeeding are the most common mistakes.
Watering
Water only when the top inch of soil feels dry. In Washington’s western regions, natural rainfall may be enough. In eastern areas, water deeply once a week during dry spells. Avoid overhead watering to prevent leaf diseases.
Deadheading And Pruning
Remove spent flowers to encourage more blooms. If plants get leggy, cut them back by one-third. They will bush out and flower again. In late summer, let some flowers go to seed for next year’s crop.
Pest And Disease Management
Aphids love nasturtiums. They are actually a good trap crop—aphids prefer nasturtiums over your vegetables. Hose them off with water or spray with insecticidal soap. Slugs can be a problem in wet areas. Use beer traps or diatomaceous earth.
Regional Adjustments For Washington
Washington’s diverse climate means one size doesn’t fit all. Here are specific tips for each region.
Puget Sound Lowlands
Mild winters and cool summers. Soil stays damp. Plant in raised beds or containers for better drainage. Use black plastic mulch to warm soil faster in spring. Expect blooms from July through October.
Columbia River Gorge
Windy and dry. Protect seedlings with windbreaks or plant near a wall. Water more frequently. The best time to plant is late May.
San Juan Islands
Cooler than the mainland. Wait until June 1-10. Use south-facing slopes for extra warmth. Container gardening works well here.
Okanogan And Methow Valleys
Hot summers and cold winters. Plant in early June. Provide afternoon shade if temperatures exceed 90°F. Water deeply but infrequently.
Common Mistakes To Avoid
Even experienced gardeners make these errors. Avoid them for a better bloom.
- Planting too early in cold, wet soil
- Using rich soil or fertilizer (too much nitrogen)
- Overwatering, especially in clay soil
- Planting in shade (fewer flowers)
- Not hardening off indoor-started plants
- Ignoring soil temperature
Harvesting And Using Nasturtiums
Both flowers and leaves are edible. They have a peppery, radish-like flavor. Harvest in the morning when flowers are fully open. Use them in salads, as garnishes, or infuse vinegar.
To save seeds for next year, let some flowers form seed pods. When they turn brown and dry, collect them. Store in a paper envelope in a cool, dry place. They remain viable for 3-5 years.
Frequently Asked Questions
Can I plant nasturtiums in July in Washington?
Yes, but blooms will be shorter. In western Washington, July planting gives flowers from August to first frost. In eastern areas, July is too hot for good germination.
Should I soak nasturtium seeds before planting?
Soaking overnight in warm water speeds germination, especially in cool soil. It’s optional but helpful in Washington’s spring.
Do nasturtiums come back every year in Washington?
No, they are annuals. However, they self-seed readily. If you let some flowers go to seed, new plants may appear next spring without replanting.
What is the latest time to plant nasturtiums in Washington?
For a decent bloom, plant no later than mid-July in western Washington and late June in eastern areas. Later than that, frost will cut the season short.
Can I grow nasturtiums in containers in Washington?
Absolutely. Containers warm up faster than ground soil, so you can plant a week earlier. Use well-draining potting mix and water more frequently.
Final Tips For Success
Nasturtiums are forgiving plants. Even if you miss the ideal window, they will still bloom. The key is warm soil and no frost. In Washington, patience pays off. Wait for that late May or early June warmth, and you’ll be rewarded with months of color.
If you have a short growing season, start seeds indoors. If you have heavy clay soil, use containers or raised beds. And if you forget to plant until July, try anyway—you might get a late-summer surprise.
Remember, the best time to plant nasturtium in washington is when the soil is warm and the risk of frost is gone. That’s usually late May to early June for most of the state. Check your local frost dates and soil temperature, and you’ll have a thriving patch of nasturtiums all summer long.
Happy gardening—and don’t forget to taste those peppery flowers!