When to Plant Zucchini in Colorado
Published: April 21, 2026
Colorado gardeners in Zone 6a have a 31-week growing season for zucchini (March 30 to November 1). The moderate climate supports a full warm-season crop plus an often-productive fall crop. This guide gives exact dates for Colorado based on your local frost calendar.
Zucchini Planting Dates for Colorado
| Start seeds indoors | March 9–16 |
| Last frost (average) | March 30 |
| Transplant outdoors | April 6–16 |
| Direct sow outdoors | April 6–16 |
| Expect first harvest | May 21 – May 31 |
| Fall crop start | September 6–16 |
| Fall harvest | October 21 |
| First fall frost (average) | November 1 |
Dates above assume Zone 6a, the most common zone in Colorado. Gardeners in cooler Denver (Zone 6a) plant 1–2 weeks later; warmer Colorado Springs (Zone 6b) can plant 1–2 weeks earlier.
Growing Zucchini in Colorado's Climate
Colorado's moderate Zone 6a climate is well-suited to zucchini with minimal special accommodation. The standard transplant calendar works as written, and harvest windows line up with what seed packets recommend without adjustment.
Succession planting extends your zucchini harvest significantly in Colorado. A second planting 3 to 4 weeks after the first gives you a backup in case of pest pressure and extends the total harvest window into early fall.
Common zucchini pests to watch for in Colorado include Squash Vine Borer and Squash Bug. The first line of defense is companion planting: Corn and Bush Beans planted nearby discourage several of these pests by confusing host-plant identification or repelling adults before they can lay eggs. Weekly garden walks in the early morning catch problems when they're still manageable.
Zucchini Garden Calendar for Colorado
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | — | Dormant season |
| March | Start seeds indoors | Use grow lights; warm soil to 70–75°F for best germination |
| April | Transplant outdoors | Soil temp must be 65°F+; nighttime lows above 50°F |
| May ← | First harvest window opens | Zucchini begins producing 45–55 days after transplant |
| June | Peak growth; water 1 inch/week | Monitor for pests daily; stake or support as needed |
| July | Start fall crop seeds | Fall transplants go in 8 weeks before first frost |
| August | — | Dormant season |
| September | Fall crop planting | Transplant or direct sow for fall harvest before frost |
| October | — | Dormant season |
| November | First frost approaches | Harvest remaining zucchini; cover plants on frost nights |
| December | — | Dormant season |
Zucchini Growing Tips for Colorado Gardeners
- •Start with just 1–2 plants — zucchini are so productive that more is rarely needed.
- •Harvest at 6–8 inches for peak flavor; zucchini left on the plant signals it to stop producing.
- •Colorado's moderate climate supports succession planting — sow new transplants or seeds every 3 weeks during spring to extend the harvest window into fall.
- •Plant a backup crop in early July to replace any vine borer losses in the eastern US.
Companion Planting for Zucchini in Colorado
In Colorado's moderate climate, planting zucchini with Corn and Bush Beans helps deter pests and improve soil. Avoid planting near Potato and Fennel, which inhibit zucchini growth through root chemistry or shared pest pressure. See the full zucchini companion planting guide for the complete list.
Zucchini Planting Dates by City in Colorado
Top cities in Colorado — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant zucchini in Colorado?
In Colorado (Zone 6a), start zucchini seeds indoors around March 9–16 and transplant outdoors around April 6–16 — 1 weeks after the state's average last frost of March 30.
What is the last frost date in Colorado?
Colorado's average last frost date is March 30 in the state's most common Zone 6a. Frost dates vary by city — higher elevations and northern counties run 1 to 3 weeks later than the state average. See the city list below for city-level frost dates.
Can I grow zucchini year-round in Colorado?
Not year-round — Colorado's cold season stops zucchini production. The zucchini season runs March 30 to November 1, roughly 31 weeks. A fall crop extends harvest into late autumn.
What zucchini varieties grow best in Colorado?
For Colorado's Zone 6a, Black Beauty, Costata Romanesco, and Yellow Crookneck are widely adaptable.
When do I start zucchini seeds indoors in Colorado?
Start zucchini seeds indoors in Colorado around March 9–16, which is 3 weeks before the state's average last frost of March 30. Use grow lights and keep soil temperatures at 70–75°F for fastest germination.