USDA Hardiness Zone 5b
Frost Dates for 80540 — Lyons, Colorado
Averages from Allenspark 3nw, Co US, the nearest reporting station, 9.7 miles away.
Plant tender crops after June 14, and expect the first autumn freeze around September 12. That leaves about 92 frost-free days.
- Last spring frost
- June 14
- First fall frost
- September 12
- Growing season
- 92 days
- Hardiness zone
- 5b
50% probability
50% probability
frost-free
-15 to -10°F annual low
Planting calendar for 80540
| When | What to do |
|---|---|
| April 5 – April 19 | Start peppers and aubergines indoors They need eight to ten weeks under lights before they can go out. |
| April 19 – May 3 | Start tomatoes indoors Six to eight weeks gives a transplant big enough to set fruit early. |
| May 17 – May 31 | Sow peas, spinach, lettuce, radish outdoors These tolerate light frost and prefer to germinate in cool soil. |
| June 14 onward | Transplant tomatoes, peppers, basil, squash, cucumbers The average last freeze has passed — still watch the actual forecast. |
| by June 20 | Sow the autumn crop of carrots, beets and brassicas They need about twelve weeks to size up before growth stops. |
| by August 29 | Harvest tender crops, or be ready to cover them A first freeze two weeks early is well within normal variation. |
| September 12 onward | Plant garlic, mulch beds, lift tender bulbs Garlic wants a cold spell; bare soil loses structure over winter. |
What these dates mean
Wait until after June 14 to put tender plants — tomatoes, peppers, basil, squash — in the ground. That is the date by which half of years in Lyons, Colorado are past their last freeze. Harvest before September 12, which leaves roughly 92 frost-free days.
ZIP 80540 sits in USDA hardiness zone 5b, meaning the average coldest night of the year falls between -15 to -10°F. Zone decides what survives the winter; frost dates decide when to plant each spring. They are different questions, and a plant can pass one and fail the other.
These are thirty-year NOAA averages for 1991–2020, not a forecast. Any individual year can frost two to three weeks either side of these dates, so check the actual forecast before planting out.