USDA hardiness reference
Zone 4
Zone 4 represents an average annual extreme minimum temperature band of -30°F to -20°F. It describes winter cold, not vegetable planting dates.
Colder edge-30°FZone 4a begins here
Subzone split-25°FZone 4b begins here
Warmer edge-20°FNext broad zone begins
What Zone 4 tells you
It provides a broad basis for evaluating whether a perennial plant is likely to survive a typical local winter minimum. The “a” and “b” subzones each cover five degrees.
What it does not tell you
- Your average last spring or first fall frost
- Whether the next frost will arrive early or late
- Summer heat, humidity, rainfall, or irrigation need
- Soil drainage, wind exposure, snow cover, or urban heat effects
- Whether a specific vegetable cultivar has enough time to mature
How Gardiv uses it
Zone is optional context. The annual-vegetable planner uses your editable frost dates for schedule calculations and keeps the zone out of formulas where it does not belong.