Nasturtium seeds are surprisingly sensitive to transplanting, making direct sowing timing critical. Understanding when to plant nasturtium seeds can mean the difference between a lush, blooming garden and a disappointing patch of weak plants. This guide walks you through every factor that influences the perfect planting window, so you can get it right the first time.
Nasturtiums are among the easiest flowers to grow from seed, but they have a few quirks. They dislike root disturbance, which is why direct sowing is almost always recommended. The key is to match your planting date with your local climate and the specific variety you choose.
When To Plant Nasturtium Seeds
The exact timing depends on where you live and whether you are planting in spring or fall. In most regions, the ideal window is after the last frost date when the soil has warmed to at least 55°F (13°C). Planting too early in cold, wet soil can cause seeds to rot. Planting too late may shorten the blooming season.
Understanding Your Last Frost Date
Your last frost date is the single most important reference point for spring planting. You can find this date for your area through local extension services or online gardening tools. Nasturtiums are tender annuals that cannot tolerate frost. Even a light freeze will kill young seedlings.
- Wait until all danger of frost has passed.
- Check soil temperature with a simple thermometer.
- If soil feels cold to the touch, wait another week.
Soil Temperature Guidelines
Nasturtium seeds germinate best when soil temperatures are between 55°F and 70°F (13°C to 21°C). At the lower end, germination can take 10 to 14 days. At warmer temperatures, you may see sprouts in 7 to 10 days. Do not plant if soil is below 50°F (10°C).
How To Check Soil Temperature
Use a soil thermometer inserted 2 inches deep. Take readings in the morning for consistency. If you don’t have a thermometer, watch for weeds like chickweed or dandelions—they germinate at similar temperatures.
Regional Planting Calendars
Your location heavily influences when to plant nasturtium seeds. Here are general guidelines for different climates.
Cool Climates (USDA Zones 3-5)
In northern regions with short growing seasons, wait until late May or early June. You can start seeds indoors 4-6 weeks before the last frost, but use biodegradable pots to avoid root disturbance. Transplant carefully after hardening off.
- Last frost typically in late May.
- Direct sow in early June.
- Consider using cloches or row covers for extra warmth.
Temperate Climates (USDA Zones 6-8)
These regions offer a wider planting window. Aim for mid-April to early May, after the last frost. You can also plant a second batch in late summer for fall blooms.
- Last frost usually in mid-April.
- Direct sow from mid-April through May.
- Fall planting in August for autumn color.
Warm Climates (USDA Zones 9-11)
In hot areas, nasturtiums prefer cooler months. Plant in early spring (February to March) or in fall (September to October). Avoid summer planting when heat stress causes leggy growth and fewer flowers.
- Spring planting: February to March.
- Fall planting: September to October.
- Provide afternoon shade in hot summers.
Indoor Starting Vs Direct Sowing
While direct sowing is ideal, some gardeners start seeds indoors to get a head start. If you choose this method, follow these steps carefully.
When To Start Nasturtium Seeds Indoors
Start seeds 4 to 6 weeks before your last frost date. Use deep pots or biodegradable containers to minimize root disturbance. Fill pots with seed-starting mix, plant seeds 1/2 inch deep, and keep soil moist but not waterlogged.
- Fill pots with moist seed-starting mix.
- Plant 2 seeds per pot, 1/2 inch deep.
- Cover with plastic wrap to retain moisture.
- Place in a warm spot (65-70°F).
- Remove cover once seedlings emerge.
- Provide bright light to prevent legginess.
- Harden off for 7-10 days before transplanting.
When To Direct Sow Nasturtium Seeds
Direct sowing is simpler and avoids transplant shock. Wait until soil is warm and all frost risk has passed. Prepare the bed by loosening soil to 6 inches deep and removing weeds. Plant seeds 1/2 to 1 inch deep, spacing them 10-12 inches apart for bush varieties, or 18-24 inches for trailing types.
- Soak seeds overnight to speed germination.
- Plant in full sun to partial shade.
- Water gently after planting.
- Thin seedlings to strongest one per spot.
Fall Planting For Nasturtiums
In mild climates, fall planting extends your growing season. Plant seeds 6-8 weeks before the first expected frost. Nasturtiums thrive in cooler autumn temperatures and often bloom until the first hard freeze.
Benefits Of Fall Sowing
Fall-planted nasturtiums often have fewer pest problems. Aphids and caterpillars are less active in cooler weather. The flowers also last longer because heat stress is reduced.
- Plant in late summer for fall blooms.
- Use mulch to retain soil moisture.
- Protect from early frost with row covers.
Factors That Affect Planting Time
Several variables can shift your ideal planting date. Pay attention to these factors to fine-tune your schedule.
Seed Variety
Different nasturtium varieties have slightly different needs. Dwarf varieties like ‘Alaska’ or ‘Tom Thumb’ mature faster and can be planted later. Trailing varieties like ‘Empress of India’ or ‘Jewel Mix’ need a longer growing season.
- Dwarf types: 50-60 days to bloom.
- Trailing types: 60-70 days to bloom.
- Check seed packet for specific days to maturity.
Weather Patterns
Unseasonable cold snaps or heat waves can disrupt your plans. Monitor the 10-day forecast before planting. If a cold spell is predicted, delay sowing. If a heat wave is coming, provide shade or wait for cooler weather.
Soil Quality
Nasturtiums actually prefer poor to average soil. Rich soil encourages lush leaves but fewer flowers. Well-draining soil is essential to prevent root rot. If your soil is heavy clay, amend with sand or compost to improve drainage.
Step-By-Step Guide To Planting Nasturtium Seeds
Follow this simple process for successful germination and growth.
Step 1: Prepare The Site
Choose a location with full sun (6+ hours daily) or partial shade in hot climates. Remove weeds and rocks. Loosen soil to 6 inches deep. Nasturtiums are not heavy feeders, so skip fertilizer unless soil is very poor.
Step 2: Soak Seeds (Optional)
Soaking seeds overnight in warm water can soften the hard seed coat and speed germination. This is especially helpful if soil is on the cooler side. Drain before planting.
Step 3: Plant Seeds
Make a small hole 1/2 to 1 inch deep. Drop in one or two seeds. Cover with soil and pat gently. Space according to variety. Water lightly to settle the soil.
Step 4: Water And Wait
Keep soil consistently moist but not soggy. Seeds should germinate in 7-14 days. Once seedlings have two sets of true leaves, thin to the strongest plant per spot.
Step 5: Care After Germination
Water deeply once a week, more often in hot weather. Deadhead spent flowers to encourage more blooms. Watch for aphids and treat with a strong spray of water if needed.
Common Mistakes And How To Avoid Them
Even experienced gardeners make errors with nasturtiums. Here are the most common pitfalls.
Planting Too Early
Cold, wet soil causes seeds to rot. Always wait until soil is at least 55°F. If you are unsure, do a soil temperature test.
Overwatering
Nasturtiums are drought-tolerant once established. Overwatering leads to yellow leaves and root rot. Water only when the top inch of soil feels dry.
Too Much Fertilizer
Rich soil produces many leaves but few flowers. Avoid high-nitrogen fertilizers. If your soil is fertile, plant nasturtiums in a less rich area.
Ignoring Spacing
Crowded plants compete for light and nutrients. Follow spacing guidelines on the seed packet. Proper spacing also improves air circulation, reducing disease risk.
Frequently Asked Questions
Can I plant nasturtium seeds in pots? Yes, choose containers at least 6 inches deep with drainage holes. Use well-draining potting mix. Plant 2-3 seeds per pot and thin later.
What month is best for planting nasturtium seeds? In most regions, April or May after the last frost. In warm climates, February-March or September-October works best.
How deep should I plant nasturtium seeds? Plant seeds 1/2 to 1 inch deep. Deeper planting may prevent germination, while shallower planting risks drying out.
Do nasturtium seeds need light to germinate? No, they germinate in darkness. Cover seeds with soil. Once sprouts appear, provide bright light.
Can I plant nasturtium seeds in summer? In cooler regions, summer planting is possible but may result in fewer blooms due to heat. In hot climates, avoid summer planting.
Final Tips For Success
Nasturtiums are forgiving plants once you get the timing right. They reward you with vibrant flowers and edible leaves and seeds. Remember to check your local frost dates, monitor soil temperature, and choose the right variety for your space.
If you miss the spring window, don’t worry—fall planting in mild climates can be just as rewarding. Nasturtiums are also excellent companion plants, repelling pests from vegetables like cucumbers and tomatoes.
With the information in this guide, you now know exactly when to plant nasturtium seeds for a spectacular display. Grab your seeds, check the weather, and get ready to enjoy one of the easiest and most beautiful annuals you can grow.