Knowing when to plant vegetables in Colorado is the single most important factor for a successful garden. Our unique climate, with its short growing season and unpredictable spring weather, makes timing everything. Get it right, and you’ll enjoy a bounty of fresh produce. Get it wrong, and you might be replanting after a late frost.
This guide will walk you through the optimal schedule for planting, using simple methods that local gardeners rely on. We’ll cover frost dates, soil temperature, and how to use Colorado’s distinct seasons to your advantage.
When to Plant Vegetables in Colorado
This heading is your master blueprint. The dates given here are based on average last frost dates, which vary dramatically across the state. Denver’s last frost is around May 5th, but in the mountains, it could be mid-June. Always check local resources for your specific area.
Understanding Your Colorado Growing Zone
Colorado isn’t just one garden zone; it’s many. From zones 3b in the high mountains to 7a in some warmer valleys, your location dictates your schedule. The first step is to find your USDA hardiness zone. You can do this with a quick online search using your zip code.
More crucial than zone, however, is your microclimate. South-facing slopes warm faster. Urban Denver gardens are warmer than rural Eastern Plains areas at the same latitude. Observe your own yard’s conditions—it’s the best data you have.
The Non-Negotiables: Frost Dates and Soil Temp
Your planting calendar revolves around two fixed points: the average last spring frost and the average first fall frost. The time between them is your growing season. In Boulder, that might be 157 days. In Grand Junction, it’s longer. In Crested Butte, it’s much shorter.
Even more important than air temperature is soil temperature. Seeds rot in cold, wet soil. A simple soil thermometer is a gardener’s best friend. Here are key temps:
- Cool-Season Crops (40°F+): Spinach, peas, kale, lettuce. They can germinate in cool soil.
- Warm-Season Crops (60°F+): Beans, cucumbers, zucchini. They need warmer soil.
- Heat-Lovers (70°F+): Tomatoes, peppers, eggplant, melons. Planting to early stunts them.
Spring Planting Schedule (Early March – June)
Spring planting happens in waves, not all at once. Patience is key. We start with the toughest crops and work our way to the tender ones.
Very Early Spring (2-4 Weeks Before Last Frost)
As soon as the soil is workable (not frozen or a muddy mess), you can plant these hardy seeds directly in the garden:
- Peas
- Spinach
- Kale
- Radishes
- Carrots and parsnips
Early Spring (On or Just Before Last Frost)
These crops can handle a light frost. You can plant seeds or transplants now:
- Lettuce and arugula
- Broccoli and cabbage transplants
- Potato tubers
- Swiss chard
- Beets and turnips
Late Spring (1-2 Weeks After Last Frost)
The soil is warming up. It’s time for the warm-season crops. Always be prepared to cover plants if a surprise cold snap hits.
- Direct seed: Beans, corn, cucumber, zucchini.
- Plant transplants: Early tomatoes (choose short-season varieties).
Early Summer (2-3 Weeks After Last Frost)
Now the soil is truly warm. This is the safe window for the most cold-sensitive plants. Night temps should be consistantly above 50°F.
- Plant transplants: Tomatoes, peppers, eggplant, basil.
- Direct seed: Melons, squash, pumpkins, cucumbers (succession planting).
Summer Planting for Fall Harvest (July – August)
Many gardeners miss this second season! In July, you can plant seeds for vegetables that mature in the cool, crisp fall weather, which often taste even sweeter.
Count back from your first fall frost date using the “Days to Maturity” on the seed packet. Add about 2 weeks for slower growth as days shorten. Good choices for a fall garden include:
- Lettuce and greens (plant in partial shade)
- Kale and collards
- Radishes and turnips
- Carrots (they sweeten after a frost)
- Spinach
- Peas for a fall crop
Essential Tips for Colorado’s Challenges
Our climate presents specific hurdles. Here’s how to overcome them:
- Use Season Extenders: Cold frames, row covers, and wall-o-waters are invaluable. They protect early plantings and can extend your fall harvest by weeks.
- Amend Your Soil: Colorado soil is often clay-heavy or sandy. Adding generous amounts of compost improves drainage and nutrient content, helping soil warm faster in spring.
- Water Wisely: Our air is dry. Water deeply and less frequently to encourage deep roots. Drip irrigation or soaker hoses are far more efficient than overhead sprinklers, which can promote disease.
- Watch for Hail: Have a hail protection plan. Movable containers or lightweight row covers can be thrown over plants quickly when storms threaten.
Don’t forget about wind, which can dry out plants and damage seedlings. Using windbreaks or planting in sheltered areas can make a big difference for your gardens success.
Sample Planting Calendar for Front Range (Zone 5b/6a)
Use this as a template, adjusting for your exact location:
- March 15-30: Pea, spinach, radish seeds.
- April 15-30: Carrot, beet, lettuce, kale, potato seeds/sets.
- May 1-7: Broccoli, cabbage transplants.
- May 10-15: Direct seed beans, corn, zucchini. Plant early tomato transplants.
- May 20-June 1: Plant tomato, pepper, eggplant, basil, cucumber transplants.
- July 15-31: Sow seeds for fall carrots, beets, kale, lettuce, spinach.
FAQ: Colorado Vegetable Gardening
What month do you start a garden in Colorado?
You start planning in winter! Actual planting begins in March with peas and spinach. The main planting months are April through June, with a second round for fall crops in July and August.
When should I plant tomatoes in Colorado?
For the Front Range, wait until mid-to-late May. In higher elevations, wait until early June. Ensure night temperatures are reliably above 50°F. Using a “Wall of Water” can let you plant tomatoes 2-3 weeks earlier safely.
What vegetables grow good in Colorado?
Cool-season crops excel here: leafy greens, broccoli, carrots, beets, and peas. For warm-season, choose short-season varieties of tomatoes (like ‘Early Girl’), peppers, and cucumbers. Beans, zucchini, and potatoes are also very reliable.
Is it to late to plant a garden in June?
Not at all! June is perfect for planting warm-season crops like beans, squash, and cucumbers. You can also plant fast-maturing crops like lettuce and radishes for a summer harvest, though they may need some afternoon shade.
Gardening in Colorado is a rewarding partnership with nature. By paying close attention to timing and using the right techniques, you’ll be able to grow a productive and delicious vegetable garden every year. Remember, local garden centers are a wealth of zone-specific advice, so don’t hesitate to ask them for tips.