Many deciduous fruit and nut trees need a period of cool winter conditions before buds resume normal spring growth. This seasonal requirement is commonly described as a tree’s chill requirement.
What winter chill does
As days shorten and temperatures cool, deciduous trees enter dormancy. Exposure to an appropriate amount of cool weather helps satisfy internal rest requirements so leaf and flower buds can develop normally when warmth returns.
Chill hours are an estimate
The familiar chill-hour model counts qualifying cool temperatures, but it is only one way to estimate winter chill. Other models account differently for warm interruptions and temperature ranges. Local climate data, elevation, slope, and neighborhood microclimates can all affect the chill a tree experiences.
Why variety matching matters
A variety receiving substantially less chill than it needs may show delayed or uneven leafing and flowering and may crop poorly. A very low-chill variety in a colder site may become ready to grow earlier, leaving flowers vulnerable when later frosts occur. Chill requirement is therefore one selection factor—not a guarantee of fruiting.
Find a practical local estimate
Use several years of nearby weather data when possible and consult a local Cooperative Extension office, Master Gardener program, farm advisor, or experienced nursery. Then compare the local estimate with the range listed for each variety.
Continue to the detailed guide: Fruit Tree Chill Hours Explained. For the rest of the decision process, use the bare root tree selection guide or compare bare root trees.