Zone 4

What zone 4 means

Zone 4 covers places where the average coldest night of the year falls between -30 and -20 °F (-34 to -29 °C). Zone 4a is the colder half (-30 to -25 °F) and zone 4b the warmer half (-25 to -20 °F).

A plant rated “hardy to zone 4” is expected to survive that typical winter low with its roots in the ground. 49 plants in the catalog reach the cold edge of their range here — give those a sheltered spot, good drainage and winter mulch.

What the zone doesn’t tell you

• Summer heat and humidity — many plants rated for zone 4 still fail from heat, especially in the Southeast.
• Rainfall and drainage — cold plus wet soil kills plants that would survive cold in dry soil.
• Frost dates — the length of the growing season is a separate question; check local frost dates.
• Your microclimate — walls, slopes, pavement and wind shift conditions by half a zone or more across one property.

Find your exact zone on the USDA Plant Hardiness Zone Map, then treat it as one filter among several. The planner’s OL-HARDY check uses the zone you set for the site.