Best Scientific Article “Which Way’s North” by Melanie Mason – Fall 2012

When someone says a daylily “does great in the North,” what does that really mean? In “Which Way’s North?” Melanie Mason takes a smart (and very practical) look at plant hardiness and why a single USDA zone number can’t tell the whole story.

The article explains that the USDA hardiness map is based on just one metric: the average coldest temperature in the coldest month. That’s useful but it can oversimplify what plants actually experience in real gardens.

A better way to think about “hardy”, Mason shares a Canadian approach (Oullet & Sherk, 1961) that builds a zone recommendation from seven variables gardeners recognize