When to Plant Spinach in Colorado
Published: April 24, 2026
Colorado gardeners in Zone 6a have a 31-week growing season for spinach (March 30 to November 1). Colorado's spring and fall windows both work well for spinach — some gardeners plant both successions for a long harvest. This guide gives exact dates for Colorado based on your local frost calendar.
Spinach Planting Dates for Colorado
| Start seeds indoors | Year-round |
| Last frost (average) | March 30 |
| Direct sow outdoors | February 23–March 5 |
| Expect first harvest | April 4 – April 14 |
| Fall crop start | September 20–30 |
| Fall harvest | October 30 |
| 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.
⚠ One of the earliest spring vegetables — sow 4–6 weeks before last frost. Bolts in heat above 75°F. Plant again in late summer for a fall harvest.
Growing Spinach in Colorado's Climate
Colorado's moderate Zone 6a climate is well-suited to spinach 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 spinach 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 spinach pests to watch for in Colorado include Leaf Miner and Aphid. The first line of defense is companion planting: Pea and Strawberry 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.
Spinach Garden Calendar for Colorado
| Month | Task | Notes |
|---|---|---|
| January | — | Dormant season |
| February | Direct sow seeds | Sow seeds 1/4–1/2 inch deep, 6 inches apart |
| March | — | Dormant season |
| April | First harvest window opens | Spinach begins producing 40–50 days after transplant |
| May ← | Watch for bolting | Harvest promptly; spring heat arrives quickly |
| June | — | Dormant season |
| July | — | Dormant season |
| 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 spinach; cover plants on frost nights |
| December | — | Dormant season |
Spinach Growing Tips for Colorado Gardeners
- •Direct sow in very cold soil — spinach germinates at 35°F, earlier than almost any other crop.
- •Succession plant every 10 days until 2 weeks before heat sets in for continuous spring harvests.
- •Colorado's moderate climate supports succession planting — sow new transplants or seeds every 3 weeks during spring to extend the harvest window into fall.
- •Switch to bolt-resistant varieties like Malabar or New Zealand spinach for summer heat (though technically different species).
Companion Planting for Spinach in Colorado
In Colorado's moderate climate, planting spinach with Pea and Strawberry helps deter pests and improve soil. Avoid planting near Fennel, which inhibit spinach growth through root chemistry or shared pest pressure. See the full spinach companion planting guide for the complete list.
Spinach 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 spinach in Colorado?
In Colorado (Zone 6a), start spinach seeds indoors around Year-round and transplant outdoors around null — 0 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 spinach year-round in Colorado?
spinach is a cool-season crop in Colorado, with spring and fall windows. Summer heat bolts the plants before they can produce a harvestable crop. Succession planting every 2–3 weeks stretches the harvest window.
What spinach varieties grow best in Colorado?
For Colorado's Zone 6a, consult a local nursery or extension office for spinach variety recommendations.
When do I start spinach seeds indoors in Colorado?
Spinach does not need indoor starting in Colorado — direct sow around February 23–March 5 once soil reaches 35°F. Indoor starting is not recommended for this crop because spinach transplants poorly.