Chill Hours for Fruit Trees: The Quick Answer
If you’re searching for chill hours, chill hours for fruit trees, or fruit tree chilling, here’s the simplest way to think about it: chill hours are the cool winter time many deciduous fruit trees need during dormancy so they can bloom evenly in spring. To get the most accurate estimate, check chill hours by ZIP code using a weather-station based tool.
Start here: UC Davis Chill Calculator (excellent resource for California growers).
- Need it fast? Choose a nearby weather station, then record your seasonal chill total.
- Picking trees? Choose varieties whose chilling requirement is at or below your typical local chill.
- Seeing different numbers? Tools can use different chill models (that’s normal).
Many growers also reference their USDA growing zone when choosing fruit trees. Zones help with cold tolerance, but zones are not the same thing as chill hours. Two areas in the same zone can have very different winter chilling depending on elevation, coastal influence, and microclimates.
USDA Growing Zones vs. Chill Hours: Survive vs. Thrive
It helps to think of USDA growing zones and chill hours as answering two different questions. Both matter for fruit trees, but they measure different parts of winter.
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USDA Growing Zone = “Will this tree survive my coldest winter lows?”
USDA zones are based on the average annual minimum temperature in an area. They’re primarily about cold tolerance—whether a plant can make it through the coldest nights without being killed back or damaged beyond recovery. -
Chill Hours = “Will this tree thrive and fruit reliably in my winter climate?”
Chill hours estimate how much cool weather a deciduous fruit tree experiences during dormancy. Many fruit trees need a certain amount of winter chilling to wake up and bloom evenly in spring—one of the keys to dependable fruit production.
Why this matters: You can be in a USDA zone where a fruit tree survives winter just fine, but if your area doesn’t provide enough winter chilling, the tree may leaf out or bloom unevenly and produce inconsistently. That’s why the best results come from matching both your zone (survival) and your chill estimate (performance).
What Are Chill Hours?
Chill hours are a way to estimate how much cool weather a tree experiences during dormancy. Depending on the calculator used, “chill” may be counted as hours under a certain temperature threshold (and some models weight temperatures differently). That’s why you may see different totals from different tools.
When a tree doesn’t meet its chilling requirement, it may break dormancy unevenly—leading to delayed or staggered bloom and inconsistent fruit set. Matching your climate to a variety’s chill requirement is one of the best ways to set up a new orchard for success.
How to Check Chill Hours by ZIP Code
The most practical approach is to use a chill calculator tied to nearby weather-station data. For California growers, the UC Davis Chill Calculator is a strong starting point. Another widely used option is the Mississippi State University (MSU) Chill Hours tool.
- Open a calculator (UC Davis for California; MSU is also widely used).
- Select your location (ZIP, map, coordinates, or nearest weather station—depending on the tool).
- Pick a time window (most tools summarize the winter dormancy season).
- Save your seasonal total as your planning baseline (consider checking a second nearby station if you’re in a microclimate).
- Match varieties to your result by choosing trees with chilling requirements at or below your typical local chill.
Once you know your approximate chill range, you can more confidently select trees from fruit and nut trees that fit your climate. For more planning help, explore our Organic Bare Root Fruit Trees Selection Guide and Bare Root Tree Selection Guide.
How Chill Hours Affect Fruit Tree Growth
Chill requirements vary by species and variety. Many stone fruits and pome fruits rely on adequate winter chill for strong, even bloom. If you grow blueberries too, see our blueberry chill hour guide for how chilling applies to other crops.
Too few chill hours can lead to uneven budbreak, delayed bloom, and inconsistent fruit set. On the flip side, meeting (or exceeding) a chilling requirement is generally not an issue—trees remain dormant until warming conditions trigger growth.
Recommended Fruit Trees by Chill Requirement
- Low chill (under ~300 hours): Figs, Pomegranates, Persimmons, Apriums
- Moderate chill (~300–700 hours): Peaches, Plums, Nectarines
- High chill (over ~700 hours): Apples, Pears, Cherries
Conclusion
Understanding chill hours and checking chill hours by ZIP code helps you choose fruit trees that match your winter, so bloom timing and fruit set are more consistent season after season.
12 comments
I came across chill hours first about 18 months ago after our move from the snow belt to SC. I found no real official tally of the hours anywhere locally so started a spreadsheet to do so myself. I used the ‘anything under 45’ calculation because we don’t go below freezing very often. Last year was fine – I came up with 850 hours which was fine for most of my trees. This year I have seen some limitations with straight hours. We had cold at the end of November, then record warmth in December before returning to a cold January. Consequently I restarted the calculation in January. Some of my low chill trees thought Dec warmth was spring so started flowering – not many flowers but still some. In January alone I have tallied over 300 hours. However, the trees don’t use a spreadsheet and I think the number of chill days might need to be a part of the calculation but haven’t seen that anywhere.
Kate
Terry, I would bring the tree in before it gets below freezing. I would leave it inside until you are ready to move it out in the spring. I would not move it in and out in the spring, just wait until your temps are above freezing.
Hi, So I have a Black Mission Fig tree and live in zone 6b what if I let it outside in it’s container until it got down to the lowest temperature allowed before killing it. Then brought it indoors dormant and place in a sunny window until spring? Then acclimate it to the outdoors once danger of frost is over or move it daily?
Sharon, chill is usually reported in hours and not weeks. There are charts available online or through your local ag extension that will get you approximate chill hours for your area.
How does “weeks” of chill translate into hours of chill? I am trying to figure out my bulb requirement of 12 weeks. In my area, I get about 6 hours per day at night during the winter. Daytime temps are usually in the 50”s and 60”s. I average about a 1000 hours of chill a year. Love to hear from you all.