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Last and first frost dates in Casper

United States

In Casper the last spring frost usually comes around 26 May and the first autumn frost around 3 October, which leaves about 130 frost-free days (median of 2016–2025). Tomato seedlings can go into open ground from 14 June to 25 July.

Last spring frostaround 26 May
First autumn frostaround 3 October
Frost-free days130 days

Median of 2016–2025 for the 25 km grid cell of the city: the last day at or below 0 °C in spring and the first in autumn (ERA5 reanalysis via Open-Meteo). In a cold year a frost can come a week or two later — Greenly warns 48 hours ahead.

When is the last frost in Casper?

The last frost in Casper usually comes around 26 May: that is the median of 2016–2025, so in about half of those years the last night at or below 0 °C came later. Hardy crops start before it and frost-tender ones only after it: in the table below arugula can go into open ground from 5 May, while corn waits until 6 June. The first autumn frost follows around 3 October, about 130 days later: harvest or cover frost-tender crops before then.

When to sow and plant

CropSow for seedlingsPlant out in a greenhouseOpen ground
Achocha2 April – 25 June12 May – 4 August2 June – 4 August
Ageratumfrom 29 March—from 14 June
Arugula——sow 5 May – 29 August
Basil10 May – 1 August17 June – 8 September8 July – 8 September
Beet——sow 5 May – 4 August
Bell Pepper18 April – 26 May17 June – 25 July8 July – 25 July
Black-eyed Susanfrom 11 March—from 2 June
Bok Choy7 April – 12 August12 May – 16 September2 June – 16 September
Borage——sow 2 June – 9 August
Broad bean——sow 5 May – 25 June
Broccoli——sow 5 May – 18 June
Brussels Sprouts28 February – 16 May14 April – 30 June5 May – 30 June
Busy Lizziefrom 10 March—from 2 June
Cabbage——sow 5 May – 26 May
Calendula——sow from 5 May
Carrot——sow 5 May – 11 July
Cauliflower3 March – 18 June14 April – 30 July5 May – 30 July
Celeriac24 February – 15 April12 May – 1 July2 June – 1 July
Celery24 February – 25 April12 May – 11 July2 June – 11 July
Celosiafrom 13 Aprilfrom 28 Mayfrom 18 June
Chamomile——sow 5 May – 30 July
Chayote17 February – 8 April16 May – 5 July6 June – 5 July
Chickpea——sow 5 May – 15 June
Chicory20 March – 10 July—5 May – 4 August
Chili Pepper18 April – 21 May17 June – 20 July8 July – 20 July
China asterfrom 26 Aprilfrom 17 Junefrom 8 July
Chives——sow 5 May – 21 July
Cilantro——sow 5 May – 31 July
Corn——sow 6 June – 15 June
Corn poppy——sow from 5 May
Cosmosfrom 13 Aprilfrom 28 Mayfrom 18 June
Cucumber20 May – 21 June17 June – 19 July8 July – 19 July
Daikon——sow 5 May – 28 July
Delphiniumfrom 14 February—from 5 May
Dill——sow 5 May – 10 August
Edging lobeliafrom 10 March—from 2 June
Eggplant18 April – 26 May17 June – 25 July8 July – 25 July
Florence fennel28 March – 25 June12 May – 9 August2 June – 9 August
Foxglovefrom 27 January—from 5 May
Garden sorrel——sow 5 May – 29 July
Green Beans——sow 18 June – 23 June
Hollyhock——sow from 5 May
Hyssop——sow 5 May – 21 June
Kale——sow 5 May – 23 July
Kiwano22 April – 28 June24 May – 30 July14 June – 30 July
Kohlrabi——sow 5 May – 2 August
Leek3 February – 6 April14 April – 15 June5 May – 15 June
Lemon balm——sow 5 May – 25 July
Lettuce——sow 5 May – 7 August
Lisianthusfrom 17 Januaryfrom 14 Aprilfrom 5 May
Lovage——sow from 5 May
Luffafrom 6 Mayfrom 17 Junefrom 8 July
Marigoldfrom 31 Marchfrom 12 Mayfrom 2 June
Marjoram18 April – 10 July—8 July – 8 September
Melonfrom 20 Mayfrom 17 Junefrom 8 July
Microgreens——sow 18 June – 19 September
Moringa26 April – 15 July20 June – 8 September11 July – 8 September
Moss rosefrom 17 March—from 2 June
Mustard greens——sow 5 May – 19 August
Napa cabbage9 April – 20 July12 May – 22 August2 June – 22 August
Nasturtiumfrom 4 Aprilfrom 12 Mayfrom 2 June
Okra6 May – 3 July17 June – 14 August8 July – 14 August
Oregano13 February – 30 June14 April – 29 August5 May – 29 August
Pansyfrom 17 Februaryfrom 14 Aprilfrom 5 May
Parsley——sow 5 May – 19 July
Parsnip——sow 5 May – 7 June
Peanutfrom 11 Mayfrom 17 Junefrom 8 July
Peas——sow 5 May – 21 July
Petuniafrom 15 Aprilfrom 17 Junefrom 8 July
Physalis9 April – 26 May24 May – 10 July14 June – 10 July
Pumpkin6 May – 8 June17 June – 20 July8 July – 20 July
Purple coneflowerfrom 11 February—from 5 May
Radish——sow 5 May – 3 September
Sage24 February – 26 June14 April – 14 August5 May – 14 August
Scarlet sagefrom 2 April—from 14 June
Snapdragonfrom 8 Februaryfrom 14 Aprilfrom 5 May
Soybean——sow 8 July – 15 July
Spinach——sow 5 May – 9 August
Stevia5 April – 17 May24 May – 5 July14 June – 5 July
Stock——sow from 5 May
Sunflower——sow from 18 June
Sweet alyssum——sow from 5 May
Sweet Corn26 April – 10 July18 May – 1 August8 June – 1 August
Sweet peafrom 3 Marchfrom 14 Aprilfrom 5 May
Sweet William——sow from 5 May
Swiss Chard——sow 5 May – 4 August
Thyme——sow 5 May – 15 June
Tomato2 April – 3 June24 May – 25 July14 June – 25 July
Turnip——sow 5 May – 6 August
Watercress——sow 5 May – 17 August
Watermelon20 May – 8 July17 June – 5 August8 July – 5 August
Zinniafrom 16 Mayfrom 20 Junefrom 11 July
Zucchini27 May – 26 June17 June – 17 July8 July – 17 July

Planting out: a week after the last frost once the soil is warm enough for the crop; frost-hardy crops three weeks before it; an unheated greenhouse three weeks earlier. Seedlings are sown so they are ready on that day. Each window starts on the Greenly calendar date and ends on the last day that still leaves the crop’s days to harvest (from its card) before the average first autumn frost, plus six weeks of picking for crops harvested over weeks (tomatoes, peppers, aubergines, cucumbers, courgettes, pumpkins, watermelons, beans) — our rule; earlier in the window is safer.

When the soil warms up in Casper

The day the top 7 cm of soil first averages each temperature over a week, median of 2016–2025 (ERA5 via Open-Meteo). The soil reaches 10 °C 7 days after the last spring frost and 15 °C 19 days after it.

SoilDateAgainst the last spring frost
5 °C10 May16 days earlier
10 °C2 June7 days later
15 °C14 June19 days later
18 °C8 July43 days later

Frost dates near Casper

Of the nearest cities on our list, the last spring frost ends earliest in Fort Collins (25 April) and latest in Cheyenne (12 May).

CityDistanceLast spring frostFirst autumn frost
Cheyenne226 km12 May13 October
Fort Collins275 km25 April21 October
Rapid City285 km7 May12 October
Denver362 km1 May15 October
Billings370 km25 April14 October

What to grow at home in winter in Casper

Frosts in Casper usually come from about 3 October to about 26 May. These plants have indoor care in their Greenly cards and are harvested quickly, so they can be sown on a windowsill in winter.

Planted in autumn

CropWhen to plant
Bearded Irisby 3 September
Crocusby 3 September
Daffodilby 3 September
Garlicby 3 September
Grape hyacinthby 3 September
Helleboreby 3 September
Hyacinthby 3 September
Lilyby 3 September
Ornamental onionby 3 September
Peonyby 3 September
Saffronby 3 September
Snowdropby 3 September
Tulipby 3 September
Wild garlicby 3 September

From a month before the first autumn frost, so the roots grow before winter, to the late-planting limit on each crop’s page (about two weeks before the ground freezes, by ten years of weather).