Frost Dates for Libby, MT 59923

Last spring frost June 9 · First fall frost September 11 · 94 frost-free days · USDA Zone 6a

Frost probability for 59923

Frost10%50%90%
Spring (last frost)July 4June 9May 15
Fall (first frost)August 22September 11September 29

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (50.7 km away); the 50% date is the median year.

Month by month in Libby

MonthWhat to do
JanuaryPlan your garden layout and order seeds. Research varieties suited to your frost dates.
FebruaryStart the slowest-growing crops indoors: onions, leeks, and celery (10–12 weeks before last frost).
MarchOrganize planting supplies and seed-starting mix. Check stored garden tools.
AprilStart peppers and eggplant indoors 8–10 weeks before your last frost (around June 9). Start tomatoes about two weeks later, 6–8 weeks before last frost.
MayStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
JuneLast frost around June 9. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
JulyFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
AugustFirst fall frost approaching (around September 11). Transplant fall brassicas. Sow spinach, arugula, and radishes.
SeptemberFirst frost around September 11. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
OctoberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.
NovemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.
DecemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.

What grows in a 94-day season

Frequently Asked Questions

What is the last frost date for Libby, MT (ZIP 59923)?

The median last spring frost date for Libby, MT (ZIP code 59923) is around June 9. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.

What is the first fall frost date in Libby, MT?

The median first fall frost date for Libby, MT is around September 11. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.

How long is the growing season in Libby, MT?

The frost-free growing season in Libby is about 94 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.

What USDA hardiness zone is Libby, MT?

Based on frost date patterns, Libby falls approximately in 6a. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.

When should I start tomatoes indoors in Libby, MT?

Start tomato seeds indoors 6–8 weeks before your last frost date (around June 9). For Libby, that's roughly April 14 to April 28. Transplant outdoors 1–2 weeks after your last frost.

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