These are USDA hardiness zones, and these are the normal low temperatures in winter for these areas. The zone system can help people determine which plants will thrive/survive in their area.
It's the expected lowest lows iirc. No point saying a plant would survive average winter temps if the lowest lows that can usually occur during the season would kill them
What is this and why the fuck do I have to live in the 10-20 zone?
These are USDA hardiness zones, and these are the normal low temperatures in winter for these areas. The zone system can help people determine which plants will thrive/survive in their area.
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It's the expected lowest lows iirc. No point saying a plant would survive average winter temps if the lowest lows that can usually occur during the season would kill them