Planting
A Colorado planting calendar š± is your secret weapon against the stateās unpredictable frost dates and short growing seasons.
Coloradoās high-altitude climate and unpredictable weather make timing your garden planting criticalāget it wrong, and your crops could freeze, bolt, or struggle to thrive. This month-by-month guide aligns with USDA zones 3-7, ensuring your garden thrives from early spring to late fall.
Whether youāre planting cool-season crops like peas in March or heat-loving tomatoes in June, knowing the right window saves you from wasted effort and disappointed harvests.
Iāll break down the best planting times for each region, from the Front Range to the Western Slope, so you can avoid common mistakes and maximize your yields.
Ready to transform your garden? Youāll learn how to adjust for altitude, choose the right crops for your zone, and keep your plants happy all season longāwithout guessing.
Colorado planting calendar by month: what to sow and when
Coloradoās variable frost dates and high-altitude growing zones demand precision when planning your garden. Unlike lower elevations, Denverās USDA Zone 5 can see late spring frosts until mid-May, while Colorado Springs (Zone 6) may warm up earlier.
Rural areas like the Western Slope (Zone 7) often enjoy longer growing seasons, but mountain regions (Zone 3-4) face shorter windows. Timing is everythingāplant too early, and frost will kill tender seedlings; too late, and youāll miss peak harvests.
To navigate these challenges, Iāve broken down the month-by-month planting schedule for Coloradoās diverse climates. This calendar accounts for last frost dates, soil warming trends, and altitude adjustments to help you sow with confidence.
Whether youāre a Denver urban gardener or a rural Front Range farmer, these guidelines ensure your garden thrives year-round.
Pro Tip: Use row covers or cold frames to extend your spring planting window by 2-4 weeks in high-altitude areas. For summer crops, focus on heat-tolerant varieties like zucchini and peppers, which handle Coloradoās intense afternoon sun better than delicate lettuce or spinach.
In March, focus on cool-season crops like peas and spinach, which tolerate Coloradoās chilly soils. Start tomato and pepper seedlings indoors under grow lights to give them a head start.
By mid-April, most Front Range areas (Zone 5-6) are safe for direct sowing lettuce and kale, but mountain gardeners (Zone 3-4) should wait until May 1 to avoid frost damage.
May marks the critical window for warm-season crops. Once the last frost date passes (typically April 15 in Denver and May 15 on the Western Slope), plant tomatoes, peppers, and beans.
Use black plastic mulch to warm the soil faster in high-altitude gardens. For Denver gardeners, this means late April
Best plants for Coloradoās short growing season: cool-season vs. warm-season crops
Coloradoās short growing season and high-altitude climate demand strategic plant choices. Cool-season crops thrive in spring and fall, while warm-season plants need summerās heat. Iāve tested these varieties in my Denver gardenātheyāre proven winners for USDA zones 4-7.
Start with cool-season hardies like kale and peas in early spring, then transition to tomatoes and peppers as temperatures rise.
Succession planting is key here. By staggering planting dates, you can extend harvests from May through October. For example, sow lettuce every 2 weeks in spring and basil every 3 weeks in summer.
This ensures a continuous supply of fresh produce, even with Coloradoās unpredictable weather. My highest-yielding crops? Potatoes, carrots, and Swiss chard in cool weather, and zucchini, cucumbers, and eggplant in summer.
Cool-Season vs. Warm-Season Plants for Colorado
Cool-Season Plants
- ā Pros: Hardy, early harvests, tolerate frost
- š± Best for: Spring (March-May) & Fall (Aug-Sept)
- šæ Top Picks: Kale, peas, potatoes, carrots, spinach
Plant 4-6 weeks before last frost (typically April 15 in Denver). Use row covers for extra protection.
Warm-Season Plants
- ā Pros: Fast growth, high yields, love heat
- āļø Best for: Summer (June-August)
- š¶ Top Picks: Tomatoes, peppers, basil, cucumbers, zucchini
Wait until soil is 60Ā°F+ (usually after May 15). Use black plastic mulch to warm soil faster.
Succession Planting Tips
Extend harvests by replanting every 2-3 weeks for:
- š„¬ Lettuce, spinach, radishes (cool season)
- š Tomatoes, basil, beans (warm season)
Use shade cloth in summer to protect cool-season crops from bolting.
For cool-season crops, focus on leafy greens and root vegetables. My favorite variety is āWinterborā kaleāit survives 20Ā°F and tastes sweeter after frost. Plant peas and potatoes in March for early harvests.
These crops thrive in 50-65Ā°F soil, so test temperatures before planting. In high-altitude areas, add 2-4 weeks to planting dates to account for cooler soils.
Warm-season plants need consistent warmth to thrive. Start tomatoes and peppers indoors in March, then transplant after last frost. I swear by āCherry Tomā tomatoes and āJalapeƱo Mā peppersāthey handle Coloradoās hot afternoons better than other varieties.
Use mulch to retain moisture and cage tomatoes to prevent wind damage. If summer arrives late, consider heat-tolerant varieties like āSolar Fireā peppers or āArkansas Travelerā tomatoes.
Donāt forget herbs and flowers! Basil and cilantro are warm-season heroes, while parsley and chives handle cool weather. Plant marigolds and nasturtiums alongside veggiesāthey repel pests and add color.
My go-to combo? Tomatoes with basil and carrots with parsley. This companion planting keeps pests away and maximizes space in small gardens.
Pro tip: Use container gardening for warm-season crops in cooler microclimates. Move pots to sunny spots during the day and sheltered areas at night. This extends the growing season by 2-3 weeks in Denverās urban heat islands.
For fall planting, start broccoli and cabbage in August to harvest before first frost (usually October 1).