New federal planting map recognizes warming

First revision since 1990

Matt Dietrichson, Jan 27, 12.

The color-coded map of planting zones often seen on the back of seed packets is being updated by the government, revealing hotter temperatures, according to The Houston Chronicle:

It’s the first time since 1990 that the US Department of Agriculture has revised the official guide for the nation’s 80 million gardeners, and much has changed. The hardiness map, which indicates average minimum low temperatures in specific areas, is a tool for deciding what to plant.

The new guide was unveiled Wednesday at the National Arboretum in Washington, D.C., and reflects a new reality: The coldest day of the year isn’t as cold as it used to be, so some plants and trees now can survive farther north.

In the Houston area, most of Harris County is now in zone 9a, with average minimum winter temperatures of 20 to 25 degrees. Under the previous map, only the southern half of the county was in that zone. The northern area was in 8b, with average minimums of 15 to 20 degrees. Montgomery County now straddles zones 8b and 9a.

The new categories mean gardeners in north Harris County and south Montgomery County may successfully try plants not previously recommended because of their sensitivity to cold.

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