Colorado’s unpredictable late snowstorms make planting rhubarb a gamble until May. Finding the best time to plant rhubarb in Colorado means balancing soil temperature with the risk of a sudden freeze. Rhubarb is a tough perennial, but it needs a solid start to thrive in our high-altitude climate.
You want to plant rhubarb when the soil is workable but not waterlogged. In most parts of Colorado, that window opens between mid-April and early June. The exact timing depends on your elevation and local microclimate.
Best Time To Plant Rhubarb In Colorado
The ideal planting window for rhubarb in Colorado is from late April through mid-May. This gives the roots time to establish before summer heat arrives. Soil temperature should be at least 40°F at a depth of 4 inches.
If you plant too early, a late frost can damage new growth. If you plant too late, the plant won’t have enough time to build strong roots before winter. Aim for a consistent forecast with no hard freeze in the next two weeks.
Soil Temperature Requirements
Rhubarb roots need cool soil to wake up properly. Use a soil thermometer to check the temperature. If the soil is below 40°F, wait a few more days.
- Ideal soil temperature: 40-50°F
- Minimum safe temperature: 35°F
- Maximum before stress: 60°F
Colorado soil warms slowly in spring, especially at higher elevations. In Denver, the soil often reaches 40°F by late April. In the mountains, you may need to wait until late May or early June.
Frost Date Considerations
Colorado’s last spring frost varies widely by location. Check your local frost date before planting. Rhubarb can survive light frosts, but hard freezes below 28°F can kill tender new leaves.
- Find your USDA hardiness zone
- Check historical last frost dates for your area
- Wait until after the average last frost date
- Monitor the 10-day forecast for any cold snaps
In Denver, the average last frost is around May 5. In Colorado Springs, it’s closer to May 15. In higher elevations like Leadville, frost can occur into June.
Choosing The Right Rhubarb Variety For Colorado
Not all rhubarb varieties handle Colorado’s climate well. You need a variety that tolerates cold winters and hot summers. Some varieties are more disease-resistant than others.
Top Varieties For Colorado Gardens
- Victoria: Classic variety, reliable, good for beginners
- Canada Red: Sweet stalks, less tart, good for eating raw
- Riverside Giant: Large stalks, very cold-hardy
- Valentine: Early producer, bright red stalks
- Timperley Early: Very early harvest, compact size
Avoid varieties that need long, cool growing seasons. Colorado’s summer heat can stress some rhubarb types. Stick with varieties bred for colder climates.
Where To Buy Rhubarb Crowns
You can buy rhubarb crowns from local nurseries or online suppliers. Local nurseries often carry varieties that do well in your area. Online suppliers offer more choices but ship at specific times.
- Local garden centers: Best for immediate planting
- Online seed catalogs: More variety, plan ahead
- Farmers markets: Sometimes sell divisions from local growers
Order crowns early in spring. Popular varieties sell out fast. If you order online, make sure the supplier ships at the right time for your area.
Preparing Your Soil For Rhubarb
Rhubarb grows best in well-drained soil rich in organic matter. Colorado soil is often heavy clay or sandy. You need to amend it before planting.
Soil Testing And Amendments
Test your soil pH before planting. Rhubarb prefers a pH between 6.0 and 6.8. Colorado soil is often alkaline, so you may need to lower the pH.
- Get a soil test kit from a garden center
- Send a sample to your local extension office
- Add sulfur to lower pH if needed
- Mix in 2-3 inches of compost
- Add well-rotted manure for nutrients
Work the amendments into the top 12 inches of soil. Rhubarb roots can grow deep, so loose soil helps them spread. Remove any rocks or debris that could block root growth.
Choosing The Right Location
Rhubarb needs full sun for at least 6 hours a day. In Colorado’s intense sun, some afternoon shade can help in hot areas. Choose a spot with good air circulation to prevent fungal diseases.
- Full sun: 6-8 hours daily
- Partial shade: Acceptable in hot areas
- Protect from strong winds
- Avoid low spots where frost settles
Plant rhubarb away from trees and large shrubs. They compete for water and nutrients. A dedicated bed or corner of the garden works best.
Step-By-Step Planting Guide
Planting rhubarb correctly gives it the best start. Follow these steps for success in Colorado’s unique climate.
When To Plant Rhubarb Crowns
Plant crowns as soon as the soil is workable in spring. Bare-root crowns should go in the ground within a few days of arrival. Potted plants can wait a bit longer.
- Dig a hole 12 inches deep and 18 inches wide
- Mix compost into the removed soil
- Place the crown with buds facing up
- Cover with 2 inches of soil
- Water thoroughly after planting
Space crowns 3-4 feet apart. Rhubarb plants can grow large over time. Crowded plants produce smaller stalks.
Watering After Planting
Water newly planted rhubarb deeply once a week. Colorado’s dry air and wind can dry out soil quickly. Check soil moisture by sticking your finger 2 inches into the ground.
- First month: Keep soil consistently moist
- After establishment: Water deeply once a week
- During heat waves: Water twice a week
- Reduce watering in fall
Overwatering can cause root rot. Make sure the soil drains well. If water pools on the surface, improve drainage before planting.
Caring For Rhubarb Throughout The Season
Rhubarb needs regular care to produce well for years. Colorado’s climate requires some specific attention.
Fertilizing Rhubarb
Fertilize rhubarb in early spring before growth starts. Use a balanced fertilizer like 10-10-10. Avoid high-nitrogen fertilizers that produce lots of leaves but weak stalks.
- Apply 1/2 cup of balanced fertilizer per plant
- Spread it around the base, not touching the crown
- Water in well after applying
- Repeat after harvest in early summer
Organic options include compost tea or fish emulsion. Apply these every 4-6 weeks during the growing season. Too much fertilizer can burn the roots.
Mulching For Colorado Winters
Colorado winters can be harsh on rhubarb crowns. Mulch protects the roots from freezing and thawing cycles. Apply mulch after the ground freezes in late fall.
- Use straw, leaves, or wood chips
- Apply 4-6 inches deep
- Remove mulch in early spring
- Leave a thin layer for moisture retention
Mulch also helps keep soil cool in summer. Rhubarb prefers cool roots. A 2-inch layer of organic mulch works well.
Harvesting Rhubarb In Colorado
Don’t harvest rhubarb in its first year. The plant needs time to establish. In the second year, you can take a few stalks. By the third year, you can harvest freely.
When To Harvest
Harvest rhubarb from late spring through early summer. Stalks are ready when they are 12-18 inches long. Stop harvesting by mid-July to let the plant store energy for winter.
- Grasp the stalk near the base
- Pull gently while twisting
- Leave at least half the stalks on the plant
- Remove flower stalks immediately
Flower stalks take energy away from stalk production. Cut them off as soon as you see them. The plant will focus on growing edible stalks.
Storing Fresh Rhubarb
Fresh rhubarb keeps for about a week in the refrigerator. Wrap stalks in a damp paper towel and place in a plastic bag. You can also freeze rhubarb for later use.
- Refrigerator: 5-7 days
- Freezer: Up to 12 months
- Cut into 1-inch pieces before freezing
- Blanch for 1 minute to preserve color
Frozen rhubarb works well in pies and sauces. It will be softer when thawed, so use it for cooking rather than eating raw.
Common Rhubarb Problems In Colorado
Colorado’s climate can cause specific issues with rhubarb. Knowing what to look for helps you fix problems early.
Pests And Diseases
Rhubarb is generally pest-resistant, but a few issues can occur. Aphids and slugs are the most common pests. Fungal diseases can appear in wet conditions.
- Aphids: Spray with water or insecticidal soap
- Slugs: Use beer traps or diatomaceous earth
- Root rot: Improve drainage, avoid overwatering
- Leaf spot: Remove affected leaves, improve air flow
Most problems are easy to manage if caught early. Check your plants weekly during the growing season. Remove any damaged leaves promptly.
Bolting And Flowering
Rhubarb sometimes bolts, meaning it sends up flower stalks. This happens due to stress from heat, drought, or poor soil. Remove flower stalks immediately to redirect energy to the roots.
- Cut flower stalks at the base
- Water deeply during dry spells
- Mulch to keep soil cool
- Fertilize in spring to reduce stress
Bolting doesn’t harm the plant long-term. It just reduces the harvest for that season. Next year should be better if you address the cause.
Dividing And Transplanting Rhubarb
Rhubarb plants need division every 5-7 years. This keeps them productive and healthy. The best time to divide is in early spring or fall.
When To Divide Rhubarb
Divide rhubarb when the center of the crown looks woody or unproductive. This usually happens after 5 years. Early spring, just as growth begins, is ideal.
- Dig up the entire crown
- Cut into sections with a sharp knife
- Each section should have at least one bud
- Replant immediately at the same depth
Dividing in fall works too, but the plant has less time to recover before winter. Spring division gives the best results in Colorado.
Transplanting Tips
If you need to move a rhubarb plant, do it in early spring. Dig a wide hole to get all the roots. Water well after transplanting and keep the soil moist for a few weeks.
- Prepare the new hole before digging up the plant
- Water the plant well the day before
- Dig a 12-inch radius around the crown
- Lift the plant carefully with a shovel
- Place in the new hole at the same depth
- Backfill and water thoroughly
Transplanted rhubarb may take a year to recover. Don’t harvest any stalks in the first season after moving. Let the plant focus on root growth.
Growing Rhubarb In Containers
If you have limited space, you can grow rhubarb in containers. Choose a large pot at least 18 inches wide and deep. Use a high-quality potting mix with compost.
Container Care
Container-grown rhubarb needs more frequent watering than in-ground plants. Colorado’s dry air can dry out pots quickly. Check soil moisture daily during hot weather.
- Water when the top inch of soil is dry
- Fertilize every 4 weeks during growing season
- Move pots to a sheltered spot in winter
- Wrap pots with insulation for cold protection
Rhubarb in containers may need division more often, every 3-4 years. The roots can become root-bound in a pot. Repot into a larger container when needed.
Frequently Asked Questions
Can I plant rhubarb in the fall in Colorado?
Fall planting is risky in Colorado because the plant won’t have time to establish before winter. Spring planting is much more reliable. If you must plant in fall, do it at least 6 weeks before the first hard frost.
How deep should I plant rhubarb crowns?
Plant crowns with the buds just 2 inches below the soil surface. Planting too deep can cause the crown to rot. Planting too shallow can expose roots to frost.
Does rhubarb need full sun in Colorado?
Yes, rhubarb needs at least 6 hours of direct sun daily. In very hot areas, some afternoon shade can help prevent stress. Full sun produces the strongest stalks.
How long does rhubarb take to grow from crowns?
Rhubarb from crowns will produce small stalks in the first year, but you should not harvest them. In the second year, you can take a few stalks. Full production starts in the third year.
What is the best fertilizer for rhubarb in Colorado?
A balanced fertilizer like 10-10-10 works well. Apply in early spring and again after harvest. Organic options include compost and well-rotted manure.
Planting rhubarb at the right time gives you years of harvests. Colorado’s climate requires patience and planning, but the reward is worth it. Follow these guidelines, and you’ll have healthy rhubarb plants for decades.