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Seasonal Planting Calendar

Updated May 2026 · 0 plants · 0 actions

Zone 2bNorthern TierZone 3bNorthern TierZone 4bMountain WestZone 5bMidwestZone 6aMidwestZone 7aMid-AtlanticZone 7bUpper SouthZone 8aSoutheastZone 8bPacific NorthwestZone 9aCalifornia MediterraneanZone 9bGulf Coast / SouthwestZone 10aSubtropical

Mountain West gets 128 frost-free days — enough room for one full warm-season crop and a quick cool-season second act. September is the editorial lens for what to start, transplant, and direct-seed now. Pick a USDA zone above to compare.

Zone 4b in September

☀️ In-season1 week to first frost
September is prime growing season for Mountain West — your 128-day window means every warm week counts. Transplant tomatoes and peppers once nights are reliably above 50°F, succession-sow lettuces every 2 weeks, and plan for first frost 1 weeks from now.

About Zone 4b

USDA Zone 4b (Mountain West) has an average last frost of May 20 and first frost of Sep 25, giving roughly 128 frost-free days. Cool summers, short season. Pick fast-maturing varieties. Sources: CSU Extension, USU Extension & high-altitude gardeners.

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