Growing vegetables in Montana’s short summer season can be challenging, and then rewarding. There are a few ways to achieve a more bountiful vegetable harvest. The first is by growing seeds indoors early in the season and transplanting them after the danger of frost has passed. The other important thing is to choose frost-hardy varieties.

The MontGuide “Can I Grow that Here? Vegetable and Seed Transplant Schedules for Garden or Container” is designed to help people in Montana calculate the specific time to plant seeds or start transplants, and then plant them at the proper time.

The guide includes a formula to help gardeners calculate the number of frost-free growing days. Selecting species that have fewer days to maturity will also help gardeners grow vegetables that can ripen for a few weeks or longer before a killing frost in the fall. The guide also includes a list of frosthardy species that helps ensure a more successful vegetable
harvest and helps combat the limited season in Montana’s USDA plant growing zones 3-5.

CALCULATE FROST-FREE GROWING DAYS

Define the average first frost date in the fall and the average last frost date in the spring for an area. Then, with the aid of a calendar, calculate from those dates the spring planting dates for the area and the transplant starting dates. Remember to calculate both dates if a variable is given.

Example: Weeks to transplant size, 3–5. Calculate both three weeks before the planting date and also five weeks before the planting date to give a wider range of time in which to start transplants. This is also the way to calculate planting dates if variables are given.

For example, snap beans can be planted one week before the last frost to 12 weeks before first frost. Calculate the date one week before last frost date and then the date 12 weeks before first frost. This is the planting range of time. For more information on particular varieties, check seed
packets for special instructions and transplant guidelines.

ANSWER THE QUESTION: CAN I GROW THAT HERE?

Once you know the average dates of the last frost in spring and the first frost in fall, count the number of days between. If the “days to maturity” figure for a desired vegetable is a larger number of days and the “frost tolerance” column indicates “none,” the sad truth is that particular vegetable probably won’t grow to maturity. But there are many things that can be grown in most of Montana. Begin by calculating the specific dates for your garden space. Then consider if a vegetable can be transplanted or sown outdoors within the frost-free days available.

The MontGuide lists about 30 species and the details needed to determine how to grow them successfully in Montana. A few of the more common and successful species a reincluded here.

image of carrots, peppers, kale, and beets.

Photos: Adrian Sanchez-Gonzalez and Kelly Gorham, MSU Photo

Vegetable

 Days to Maturity Spring/Fall Planting Dates Weeks to Transplant Size Sun Requirement Frost Tolerance Greenhouse Grown? Soil Temperature for Germination
Snap Beans 52-70 1 week before last
frost to 12 weeks
before first frost		 Direct seed Full sun None No 60–85° F
Beets 50-80 4 weeks before last
frost to 8–10 weeks
before first frost		 Direct seed Full sun Hardy No 50–75° F
Broccoli 60-80 after transplanting 6 weeks before last
frost to 14 weeks
before first frost		 6-8 weeks At least 5
hours daily		 Hardy No 50–65° F
Carrots 60-80 after direct seeding 4 weeks before last
frost to 13 weeks
before first frost		 Direct seed At least 5
hours daily		 Hardy No 55–75° F
Cucumbers 50-70 1 week before last
frost to 12 weeks
before first frost		 4 weeks At least 5
hours daily		 None Yes 65–85° F
Kale 55-75 after direct seeding Spring — 5 weeks
before last frost to 2
weeks after last frost		 Direct seed At least 5
hours daily		 Hardy No 40–70° F
Lettuce 40-60 after direct seeding; 25-35 after transplanting 4 weeks before last
frost to 6 weeks
before first frost		 4-6 weeks At least 5
hours daily		 Hardy Yes 45–75° F
Onions 40-70 from sets For sets and seeds —
3 weeks before last frost
to 2 weeks after last frost		 4-8 weeks At least 5
hours daily		 Hardy Yes 50–80° F
Peas 55-90 after direct seeding Spring — 4–6 weeks
before last frost to 2–3
weeks after last frost		 Direct seed Full sun Very hardy No 40–70° F
Peppers 50-75 after transplanting 1 week before last
frost to 17 weeks
before first frost		 6-8 weeks At least 6
hours daily		 None No 65–85° F
Potatoes 80-140 1 week before last
frost to 17 weeks
before first frost		 Direct plant Full sun Vegetation tender; tubers hardy No 60–65° F
Summer Squash 45-60 after transplanting From last frost
to 10 weeks before
first frost		 4 weeks Full sun None No 65–85° F
Tomatoes 70 after transplanting 1 week before last
frost to 17 weeks
before first frost		 6-10 weeks At least 8
hours full
sun daily		 None Yes

65–85° F

 

 

Adapted from the MontGuide “Can I Grow That Here?” (MT199308AG) by Amy Grandpre, former MSU Extension Horticulture Assistant, Yellowstone County.