Best Time To Plant Geranium In Colorado

Colorado’s dramatic temperature swings between day and night affect when geraniums can go outside, so knowing the Best Time To Plant Geranium In Colorado is crucial for success. Many gardeners rush to set out plants after the last frost, only to lose them to a late spring snow or a cold snap. This guide walks you through exactly when and how to plant geraniums for vibrant blooms all summer.

The ideal window for planting geraniums outdoors in Colorado is from mid-May to early June. This timing avoids the most common frost dates and gives the soil time to warm up. In higher elevations, you may need to wait until late June.

Geraniums are tender perennials that cannot handle freezing temperatures. Even a light frost can kill them. So patience is key.

Here is a quick breakdown by region:

Denver and Front Range: Mid to late May
Colorado Springs: Late May to early June
Mountain towns (like Breckenridge, Aspen): Late June to early July
Western Slope (Grand Junction): Early to mid-May

Always check your local frost forecast before planting. A sudden cold front can happen even in June.

Understanding Colorado’s Unique Climate

Colorado’s weather is famous for its unpredictability. You can have a 70°F day followed by a 30°F night. This is tough on geraniums.

Geraniums prefer consistent temperatures above 50°F at night. When nights dip below 40°F, the plants get stressed. Leaves may turn yellow or drop off.

Another factor is the intense sun at high altitude. Colorado gets more UV radiation than lower elevations. Young geraniums can get sunburned if planted too early without hardening off.

Wind is also a problem. Colorado’s dry winds can dry out soil quickly and damage tender leaves. Plant in a sheltered spot or use windbreaks.

Hardening Off Your Geraniums

You cannot just take a geranium from a greenhouse and stick it in the ground. That is a recipe for shock. Hardening off is the process of gradually acclimating plants to outdoor conditions.

Start hardening off about two weeks before your planned planting date. Here is a simple schedule:

Day 1-3: Place geraniums outside in a shady, sheltered spot for 1-2 hours. Bring them back inside at night.
Day 4-6: Increase outdoor time to 3-4 hours. Add some morning sun.
Day 7-9: Leave them out for 5-6 hours, including afternoon sun. Protect from wind.
Day 10-12: Leave them out all day, but bring them in at night if temps drop below 50°F.
Day 13-14: Leave them out overnight if temperatures stay above 50°F. They are now ready to plant.

This process reduces transplant shock and helps geraniums adapt to Colorado’s harsh conditions. Do not skip it.

Choosing The Right Geranium Variety

Not all geraniums are equal in Colorado. Some handle heat and drought better than others. Here are the best types for our state:

Zonal geraniums: Most common. They tolerate heat and some drought. Great for containers and beds.
Ivy geraniums: Trailing types perfect for hanging baskets. They need more water and shade from afternoon sun.
Scented geraniums: More drought-tolerant. They have fragrant leaves and smaller flowers. Good for dry areas.
Regal or Martha Washington geraniums: Prefer cooler temperatures. They bloom best in spring and early summer. Not ideal for hot Colorado summers.

For most Colorado gardens, zonal geraniums are the safest bet. They are tough and reliable.

Preparing The Soil

Geraniums need well-draining soil. Colorado’s native soil is often heavy clay or sandy. Both need amendment.

Test your soil drainage before planting. Dig a hole 12 inches deep and fill it with water. If it takes more than 4 hours to drain, your soil is too heavy.

To improve drainage, mix in:

Compost or aged manure
Perlite or coarse sand
Peat moss or coconut coir

For containers, use a high-quality potting mix. Do not use garden soil in pots. It compacts and holds too much water.

Geraniums prefer a soil pH between 6.0 and 7.0. Colorado soil is often alkaline. You can lower pH with sulfur or peat moss if needed.

Planting Step By Step

Once the soil is ready and the weather is warm, follow these steps:

Choose a sunny spot: Geraniums need at least 6 hours of direct sun daily. Morning sun with afternoon shade works well in hot areas.
Space plants properly: Zonal geraniums need 12-18 inches apart. Ivy geraniums can be closer, about 10-12 inches.
Dig holes: Make holes twice as wide as the root ball but no deeper. The top of the root ball should be level with the soil surface.
Remove from pot: Gently loosen the roots if they are circling. Do not break the root ball apart.
Place in hole: Set the plant in and backfill with soil. Press down gently to remove air pockets.
Water thoroughly: Give each plant a good soak right after planting. This settles the soil.
Mulch: Apply a 2-inch layer of organic mulch around the base. This keeps soil cool and moist.

Water deeply once a week, more often in hot weather. Geraniums prefer to dry out between waterings. Overwatering causes root rot.

Fertilizing For Best Blooms

Geraniums are heavy feeders. They need regular fertilizer to keep blooming from June through October.

Use a balanced, water-soluble fertilizer like 10-10-10 or 20-20-20. Apply every two weeks during the growing season.

Alternatively, use a slow-release granular fertilizer at planting time. This feeds plants for several months.

Stop fertilizing in late August. This allows plants to slow down before the first frost.

Too much nitrogen causes lush leaves but few flowers. Stick to a balanced formula.

Common Problems And Solutions

Geraniums are generally easy, but Colorado conditions cause some issues. Here are the most common:

Yellow leaves: Usually from overwatering or poor drainage. Let soil dry out between waterings.
Leggy growth: Not enough sun. Move plants to a brighter spot.
No flowers: Too much nitrogen or not enough light. Switch to a bloom-boosting fertilizer.
Powdery mildew: Common in humid conditions. Space plants for airflow and avoid overhead watering.
Pests: Aphids and whiteflies can be a problem. Spray with insecticidal soap or neem oil.

Deadhead spent flowers regularly. This encourages more blooms and keeps plants tidy.

Extending The Season

Colorado’s growing season is short, especially in the mountains. You can extend it with a few tricks:

Use row covers or cloches: These protect plants from light frosts in spring and fall.
Plant in containers: You can move pots indoors when frost threatens.
Choose early-blooming varieties: Some geraniums flower faster than others.
Start indoors: Sow seeds 8-10 weeks before the last frost for earlier blooms.

With protection, you can often enjoy geraniums until late October in lower elevations.

Overwintering Geraniums

Many Colorado gardeners save their geraniums from year to year. It is easy and saves money.

Before the first hard frost, dig up your geraniums or bring pots inside. Cut back the stems to about 6 inches. Remove all leaves.

Store them in a cool, dark place like a basement or garage. Ideal temperature is 45-50°F. Do not let them freeze.

Check monthly for mold or shriveling. Lightly mist the roots if they look dry.

In late winter, pot them up and place in a sunny window. Water sparingly until new growth appears. Harden off and plant outdoors after the last frost.

This method works well for zonal and scented geraniums. Ivy geraniums are harder to overwinter.

Frequently Asked Questions

Can I plant geraniums in Colorado in April?

Only if you are prepared to protect them from frost. April is risky in most parts of Colorado. Wait until May for safer results.

What is the last frost date for Denver?

Typically around May 5-10. But frost can occur later. Always check the extended forecast before planting.

Do geraniums need full sun in Colorado?

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

How often should I water geraniums in Colorado?

Once a week deeply is usually enough. In hot, dry weather, you may need to water twice a week. Check soil moisture before watering.

Can I grow geraniums from seed in Colorado?

Yes, but start seeds indoors 8-10 weeks before the last frost. Geraniums are slow to germinate and grow. Transplants are easier for most gardeners.

Final Tips For Success

Planting geraniums in Colorado is not hard if you follow the timing. Wait until the soil is warm and nights are above 50°F. Harden off your plants. Give them good soil and regular care.

Remember that Colorado’s weather can change fast. Keep an eye on the forecast and be ready to cover plants if a cold snap hits. A little preparation goes a long way.

With the right timing and care, your geraniums will bloom from June until the first fall frost. They add bright color to patios, gardens, and window boxes. Enjoy the process and the beautiful results.

If you have more questions about growing geraniums in Colorado, ask your local extension office or garden center. They know the specific conditions in your area.

Happy planting, and may your geraniums thrive in the Colorado sunshine.