Find your estimated winter chill right here, then use it to help choose suitable fruit trees and other plants. Our ZIP-code tool uses the same Peaceful Valley database as the chill-hour lookup on Grow Organic product pages. You do not need to leave this article to get your estimate.
Ready to use your winter-chill estimate? Open the Bare Root Orchard Planner to look up your ZIP code, compare trees for your growing zone, and consider pollinizer partners and planting space.
Find Your Estimated Winter Chill
Enter the ZIP code where you plan to plant. We’ll check Peaceful Valley’s stored database for your USDA growing zone and estimated winter chill.
Use the ZIP lookup on a plant product page to check estimated winter chill.
Historical estimates help you compare varieties. They are not a forecast or a measurement at your exact planting site.
If you grow apples, peaches, cherries, plums, apricots, pears, or other deciduous fruit trees, winter chill can be just as important as summer sun. Many fruit varieties need a certain amount of cool winter weather before they can leave dormancy and grow normally in spring.
That requirement is commonly described as chill hours, although researchers and growers also use other chill models. Understanding the idea can help you avoid choosing a variety that is poorly matched to your winter climate.
What Are Chill Hours for Fruit Trees?
Chill hours are a way of estimating the amount of cool weather a deciduous plant receives during dormancy. A traditional model often counts hours within a defined cool-temperature range, but not every model calculates winter chill in the same way.
That is why a chill-hour number should be treated as a useful selection guide rather than a perfectly precise measurement for every garden.
Fruit trees use winter conditions as part of their dormancy cycle. When a variety does not receive enough appropriate winter chill, spring growth and flowering can be delayed or uneven. Poor bloom can also reduce fruit set.
Chill Hours, Chill Units and Chill Portions
Traditional chill-hour models are one way to estimate winter chill, but they are not the only approach. Researchers and growers may also use chill units or chill portions to describe how winter temperatures contribute to dormancy.
These models do not always produce directly comparable numbers. A chill total can vary depending on the calculation method and the weather data used.
If a university, agricultural program, or regional weather resource recommends a particular chill model for your area, use that guidance when comparing your local winter conditions with fruit-tree requirements.
For additional background, see the UC Davis explanation of chilling hours, units, and portions.
Chill Hours Are Not the Same as USDA Hardiness Zones
USDA Plant Hardiness Zones describe average annual extreme minimum winter temperatures. They help gardeners understand whether a perennial plant can tolerate typical winter cold in a region.
Chill requirements answer a different question: does the winter provide enough cool conditions for a particular deciduous fruit variety to satisfy dormancy?
This distinction is especially important in mild-winter climates. Two varieties may both tolerate the same USDA zone but require very different amounts of winter chill.
Check your USDA growing zone, then use the Bare Root Tree Selection Guide to evaluate the other characteristics that matter when choosing a fruit tree.
How to Use Your Chill-Hour Result
- Enter your planting ZIP code above. Use the location where the plant will grow, which may differ from your billing or shipping address.
- Read your estimated range. A result of 650–900 hours describes historical variation between winters. It is not a requirement for every plant in that ZIP code.
- Compare varieties. Open a fruit tree product page and check its listed chill-hour requirement. Where available, enter your ZIP in the product-page lookup to see the comparison automatically.
- Check the whole planting fit. Review USDA zone, pollination partners, mature size, sunlight, drainage, and bloom timing before selecting a variety.
The article tool provides your area's estimate. Plant-specific outlook messages appear on product pages because the comparison also needs that variety's listed chill requirement.
What the Chill-Hour Outlook Means
- Favorable chill-hour outlook: The lower end of your area’s estimated range meets or exceeds the upper end of the plant’s listed requirement.
- Chill hours may vary by winter: The estimated range overlaps the listed requirement. Some winters may provide less chill than the variety needs.
- Lower chill than recommended: Even the upper end of the estimated range is below the lower end of the listed requirement. Consider varieties with lower chill needs.
For example, ZIP code 95746 in Granite Bay, California has an estimated range of 650–900 hours. Red Baron Peach lists 250–300 hours, so the comparison shows a favorable chill-hour outlook. The USDA zone match is assessed separately.
If a plant's requirement is unclear or uses an incompatible chill model, an automatic outlook may not appear. A USDA zone match and a chill-hour outlook answer different questions; review both.
What if My ZIP Code Has No Chill-Hour Estimate?
Our database does not cover every ZIP code. This article's tool will tell you when a chill estimate is unavailable and show your USDA growing zone if we have it. On product pages, we omit the chill-hour section when local chill data is unavailable and show the USDA information we have.
Missing data does not mean zero chill hours, and it does not mean a plant has no chill requirement. You can start with your USDA growing zone and use local Extension or weather-station resources to investigate winter chill before choosing a variety. Zone alone cannot establish that a plant's chill needs will be met.
About Your Winter Chill Estimate
Peaceful Valley developed a database of local winter chill estimates to help you compare plants while you shop. The tool uses stored historical information and displays a 10-year modeled historical range · November–February.
The range reflects variation between winters. It is not this winter's running total, a forecast, or a measurement at your exact planting site. Elevation, terrain, and other local conditions can affect the chill your plants receive.
Calculated by Peaceful Valley from Copernicus ERA5 hourly temperatures.
Use the estimate alongside the variety's listed chill requirement and USDA zone. Published requirements may use different chill models, so the numbers are not always directly comparable. A favorable outlook is a useful selection guide, not a guarantee of flowering or fruit production.
For a difficult site or a variety near your area's estimated limit, supplement the tool with local Extension advice or representative local weather information.
Resources for Learning More About Winter Chill
Our lookup gives you a starting point without having to assemble weather records yourself. For more detail, use the UC Davis guide to chilling hours, units, and portions and your local Cooperative Extension office. Representative weather-station records or reliable measurements from your planting site can add useful local context.
When another tool gives a different result, check its temperature thresholds, winter dates, historical period, and location before comparing numbers. Some tools show this winter's accumulated chill; ours shows a stored historical range. Chill portions and chill units are not interchangeable with chill hours.
Why Chill Estimates Can Differ
You may see different chill totals for the same region. This does not always mean one source is wrong. Different models can treat temperatures differently, and weather stations may be located in different microclimates.
Traditional chill-hour models are easy to understand, but other systems such as chill units or chill portions may better describe dormancy in some climates. If a university or agricultural program in your region recommends a particular model, use that local guidance when comparing fruit varieties.
When comparing data from different sources, make sure you understand which chill model is being used. A number calculated using one model should not automatically be treated as equivalent to a number calculated using another.
What Happens if a Fruit Tree Does Not Get Enough Chill?
Insufficient winter chill can lead to delayed or uneven budbreak, weak or extended flowering, and reduced fruit set. The severity varies by species, cultivar, weather, and how far the tree is from its normal chill requirement.
This is why gardeners in warm-winter areas should pay close attention to low-chill varieties. A tree that is cold-hardy enough to survive winter is not automatically well suited to a mild winter.
Can a Fruit Tree Get Too Much Chill?
Once a tree’s dormancy requirement is satisfied, additional cool weather is not usually discussed in the same way as insufficient chill. The larger concern may shift to how early warmth and later frost affect bud development and flowers.
In colder climates, hardiness and spring frost risk may be more limiting than meeting a minimum chill requirement.
How to Use Chill Requirements When Shopping for Fruit Trees
Start with your local winter chill estimate, then compare it with the chill requirement listed for the variety. Avoid choosing a tree that sits at the edge of what your location can reliably provide unless you understand the risk.
Also check:
- USDA hardiness zone
- mature tree size
- rootstock when listed
- pollination requirements
- bloom and harvest timing
- planting-site sun and drainage
Chill is one part of fruit-tree selection, not the entire decision.
Low-Chill Fruit Trees
Gardeners in mild-winter regions should focus on varieties bred or selected for lower chill requirements. Grow Organic’s Low Chill Bare Root Trees collection can help narrow the current assortment, but always verify the stated chill requirement on the individual product because requirements differ by variety.
For broader orchard planning, return to the Bare Root Tree Selection Guide. It combines climate, size, rootstock, pollination, and site considerations without duplicating the detailed chill information on this page.
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.