Chill Hours: Why a Peach That Fruits in Georgia Can Fail in Florida

By Growing Home Greens Team · August 11, 2026

A fruit tree rated for your USDA hardiness zone can still fail to fruit reliably, and chill hours are usually why. It’s a separate measurement from cold hardiness, and skipping it is one of the most common mistakes in choosing a fruit tree variety.

What a chill hour counts

A chill hour is one hour of winter temperature between 32°F and 45°F. Most deciduous fruit trees need a minimum number of these hours to break dormancy properly and bloom on a normal schedule the following spring. It isn’t about surviving cold, that’s what hardiness zone measures, it’s about getting enough of it. A tree that doesn’t accumulate its required chill hours over the winter often blooms erratically, late, or barely at all the following spring.

The range is wide, and variety-specific

Chilling requirements vary enormously even within one type of fruit. Peach varieties alone range from as few as 200 hours up to 1,000 or more, depending on the variety, which is why “a peach tree” isn’t a useful shopping category on its own; the specific variety’s chill-hour rating is what determines whether it belongs in a given climate.

Why hardiness zone alone isn’t enough

Zone and chill hours measure different things, and a tree can be rated correctly for its zone while being completely wrong for its chill hours. A high-chill variety planted somewhere with a mild, short winter simply never accumulates enough cold hours to break dormancy normally, so it blooms sparsely and unpredictably, or not at all, even though the tree itself survives the winter without damage. The reverse causes a different failure: a low-chill variety planted somewhere with a long, cold winter can satisfy its chilling requirement early and start blooming during a mid-winter warm spell, only to lose the entire bloom to the next hard frost.

How to use the number

Look up your area’s average chill hours (your local cooperative extension office tracks this, and it varies more by microclimate than hardiness zone does) before buying, not after. Match the variety’s stated chill-hour requirement to that local average rather than assuming zone compatibility is the whole story. This is the single most common reason a fruit tree that should grow fine in a given climate never produces a real crop.

Sources: Tree Fruit: What are chill hours?, Mississippi State University Extension; How to Grow Peaches in Your Garden, Utah State University Extension.

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Chill Hours: Why a Peach That Fruits in Georgia Can Fail in Florida: Chill hours, not hardiness zone, are the reason the same peach variety thrives in one warm climate and never fruits in another. Here's what the number means and how to use it.

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