Best Time To Plant Nasturtium In Colorado

Colorado’s high altitude means nasturtium should be planted after the last snowmelt in late spring. Finding the Best Time To Plant Nasturtium In Colorado is key to getting those vibrant blooms before the first fall frost. This guide walks you through the exact timing, soil prep, and care steps for a successful nasturtium patch in the Centennial State.

Nasturtiums are one of the easiest flowers to grow from seed. They thrive in Colorado’s sunny days and cool nights. But get the timing wrong, and a late freeze or early snow can wipe them out.

Let’s break down the calendar, the microclimates, and the tricks that work for Colorado gardens. You’ll have a clear plan by the end of this article.

Understanding Colorado’s Growing Zones

Colorado spans USDA hardiness zones 3 through 7. Your exact “best time to plant nasturtium in colorado” depends on your elevation and local weather patterns.

Denver and the Front Range sit in zones 5b to 6a. The mountains, like Leadville or Breckenridge, are zones 3 or 4. The Western Slope, around Grand Junction, can be zone 7a.

Nasturtiums are tender annuals. They cannot handle frost. A single night below 32°F will kill them. So you must wait until the soil is warm and all frost danger has passed.

Last Frost Dates By Region

Here are average last frost dates for major Colorado areas:

Denver Metro: May 5 to May 15
Colorado Springs: May 10 to May 20
Boulder: May 5 to May 15
Fort Collins: May 10 to May 20
Grand Junction: April 20 to May 5
Durango: May 15 to May 25
High Mountains (above 8,000 ft): June 1 to June 15

These dates are averages. Colorado weather is unpredictable. A snowstorm in mid-May is common. Always check the 10-day forecast before planting.

The ideal window is two weeks after your last average frost date. By then, the soil has warmed to at least 55°F. Nasturtium seeds germinate best in soil temperatures between 55°F and 65°F.

For most Front Range gardeners, that means planting between May 15 and June 1. For mountain gardeners, wait until mid-June. For the Western Slope, you can plant as early as late April.

If you plant too early, seeds may rot in cold, wet soil. If you plant too late, the plants might not bloom before the first fall frost, which hits in September or early October in higher elevations.

Soil Temperature Check

Don’t rely on the calendar alone. Use a soil thermometer. Insert it 2 inches deep in the morning. If it reads 55°F or higher for three consecutive days, it’s safe to plant.

You can also use a simple trick: sit on the ground in shorts. If it feels warm to your skin, it’s warm enough for nasturtiums.

Preparing Your Colorado Garden For Nasturtiums

Colorado soil is often clay-heavy and alkaline. Nasturtiums prefer lean, well-drained soil. Too much fertility leads to lots of leaves and few flowers.

Here is how to prep your planting area:

Choose a sunny spot. Nasturtiums need at least 6 hours of direct sun daily. In Colorado’s intense sun, some afternoon shade is fine, especially at lower elevations.
Amend the soil lightly. Mix in an inch of compost if your soil is very compacted. Do not add fertilizer. Nasturtiums bloom best in poor soil.
Ensure drainage. If water pools after rain, build a raised bed or mound the soil. Wet roots cause rot.
Remove rocks and debris. Colorado soil is full of stones. Clear the area so seeds can sprout easily.

Seed Starting Indoors

You can start nasturtium seeds indoors 2 to 4 weeks before your last frost date. This gives you a head start, especially in short-season mountain gardens.

Use biodegradable pots. Nasturtiums have fragile taproots and dislike transplanting. Plant 2 seeds per pot, 1 inch deep. Keep the soil moist and warm (65°F to 70°F).

Harden off seedlings by placing them outside for a few hours each day for a week before transplanting. Move them to the garden after the last frost.

Direct Sowing Nasturtium Seeds

Direct sowing is the easiest method. Nasturtiums germinate quickly in warm soil. Here is the step-by-step process:

Soak seeds overnight. Nasturtium seeds have a hard coat. Soaking for 12 to 24 hours softens the shell and speeds germination.
Plant seeds 1 inch deep. Space them 10 to 12 inches apart for bush varieties, or 18 inches apart for trailing types.
Water gently. Use a spray nozzle to avoid washing seeds away. Keep the soil moist but not soggy.
Watch for sprouts. Seeds usually emerge in 7 to 14 days. If the soil is cooler, it may take up to 3 weeks.
Thin seedlings. Once they have two sets of true leaves, thin to the strongest plant per spot.

Succession Planting For Continuous Blooms

To extend your nasturtium season, plant a second batch 3 weeks after the first. This works well in areas with a long growing season, like the Front Range or Western Slope.

In mountain gardens, skip succession planting. Your growing window is too short. Stick with one main planting in early June.

Caring For Nasturtiums In Colorado’s Climate

Nasturtiums are low-maintenance, but Colorado’s dry air and intense sun require some attention.

Watering

Water deeply once a week, or more often if the soil dries out quickly. Colorado’s low humidity means evaporation is high. Check the soil 2 inches down. If it feels dry, water.

Water at the base of the plant. Wet leaves can lead to powdery mildew, a common issue in Colorado’s dry climate when nights are cool.

Fertilizing

Do not fertilize. Nasturtiums bloom best when stressed. Extra nitrogen produces lush leaves but few flowers. If your soil is very poor, a single application of compost tea at planting time is enough.

Pest Management

Nasturtiums attract aphids. This can be a good thing—they act as a trap crop, drawing aphids away from your vegetables. If aphids become too many, spray them off with a strong stream of water.

Slugs and snails are rare in Colorado’s dry climate. But in irrigated gardens, watch for them in shady, damp spots. Hand-pick them at night.

Deadheading

Remove spent flowers to encourage more blooms. Nasturtiums are self-cleaning to some degree, but deadheading keeps the plant tidy and productive.

You can also harvest the flowers and leaves for salads. They have a peppery, radish-like flavor. The seeds can be pickled as a caper substitute.

Common Mistakes When Planting Nasturtiums In Colorado

Even experienced gardeners make these errors. Avoid them for a better harvest of blooms.

Planting too early. A late spring snow can kill seedlings. Wait until the soil is warm.
Over-fertilizing. Rich soil equals big leaves, few flowers. Nasturtiums thrive on neglect.
Planting in full shade. They need sun to bloom. Too much shade produces leggy plants.
Ignoring drainage. Colorado clay holds water. Raised beds or mounds prevent root rot.
Not soaking seeds. Hard seed coats delay germination. Soaking gives you faster results.

Nasturtium Varieties For Colorado Gardens

Choose varieties that handle Colorado’s conditions well. Here are top picks:

Jewel Mix: Compact, bushy plants with bright flowers. Good for borders and containers.
Alaska Mix: Variegated leaves with cream and green patterns. Tolerates partial shade.
Empress of India: Deep crimson flowers and blue-green leaves. Compact and heat-tolerant.
Moonlight: Trailing variety with pale yellow flowers. Great for hanging baskets.
Cherry Rose: Double flowers in pink and rose. Attracts pollinators.

All these varieties grow well in Colorado’s climate. Choose based on your space and color preference.

Extending The Blooming Season

Colorado’s first fall frost can come as early as mid-September in the mountains, or late October on the Front Range. Here is how to get the most from your nasturtiums:

Mulch the soil. A 2-inch layer of straw or shredded leaves keeps roots cool and moist.
Provide afternoon shade. In hot areas, shade cloth or planting near taller plants reduces heat stress.
Water consistently. Drought stress stops blooming. Keep soil evenly moist.
Cover plants during early frost. Use a frost cloth or old sheet if a light frost is forecast. Remove it in the morning.

Nasturtiums will keep blooming until a hard freeze kills them. In mild years, you may enjoy flowers into November on the Front Range.

Frequently Asked Questions

When Should I Plant Nasturtium Seeds In Colorado?

Plant after the last frost, when soil reaches 55°F. For most of Colorado, that is mid-May to early June. In high mountains, wait until mid-June.

Can I Plant Nasturtiums In July In Colorado?

Yes, but only if you have at least 60 days before the first fall frost. On the Front Range, July planting works. In the mountains, it is too late.

Do Nasturtiums Need Full Sun In Colorado?

They need at least 6 hours of direct sun. In hot areas like Grand Junction, some afternoon shade helps prevent leaf scorch.

How Deep Should I Plant Nasturtium Seeds?

Plant seeds 1 inch deep. Soak them overnight first for faster germination. Space seeds 10 to 12 inches apart.

Why Are My Nasturtiums Not Blooming In Colorado?

Too much fertilizer, too much shade, or too little water are common causes. Also, check if you planted too late. Nasturtiums need warm soil to bloom.

Final Tips For Colorado Nasturtium Success

Nasturtiums are forgiving plants. Even if you miss the ideal window, they often surprise you. Here are a few last pointers:

Plant in a spot you see daily. The bright flowers and edible leaves are a treat.
Use them as a companion plant near vegetables. They repel some pests and attract beneficial insects.
Let some flowers go to seed. Nasturtiums self-sow easily. Next year, you may get volunteers.
Harvest leaves and flowers regularly. This keeps the plant producing more.

Colorado’s short growing season does not have to limit your garden. With the right timing and a little care, nasturtiums will reward you with months of color. Start planning your planting date now, and enjoy the show.

Remember, the key is patience. Wait for warm soil. Avoid the temptation to plant early. Your nasturtiums will thank you with vigorous growth and abundant blooms.