Chill Hours for Every Plant We Sell

Every fruit tree and berry bush needs a certain amount of winter cold before it'll wake up and bloom properly. That's its chill requirement, counted in chill hours. We dug up the best published figure for every plant we sell, and where nobody has published one, we worked out a careful estimate and said so. Below is the whole list, plus a calculator that counts the chill your own winters deliver.

Chill hours for everything we sell

The number is our best single figure in hours at or below 45°F. The bar shows the likely range. "How sure" tells you where the number came from. Tap a name to see the plant, or "sources" to see exactly how we got the figure.

What's a chill hour?

A chill hour is an hour of cold while the plant is dormant. Most nurseries and extension guides count every hour at or below 45°F (7°C), and that's the scale we use. Once a tree has banked enough of them, it's ready to grow, and from then on it just waits for spring warmth. If it never gets enough, it wakes up late and ragged: bloom drags on for weeks, leaves come out sparse or bunched at the branch tips, and the crop suffers.

Researchers count chill a few different ways. Some only count hours between 32 and 45°F. The Utah model gives no credit at all below about 34°F and even subtracts warm hours, and the Dynamic model counts "chill portions." In mild climates, where almost no winter hours fall below freezing, these counts land close together. In cold climates they split wide apart, because so much of winter sits below 32°F. Minneapolis averages about 2,710 hours at or below 45°F from November through February, but only about 660 of them fall between 32 and 45°F.

Chill isn't the same as cold hardiness. Hardiness is how cold a dormant plant can survive. Chill is how long it needs to stay cold before it'll grow. For hardiness, use our cold hardiness calculator.

Real winters, counted

We ran the same count the calculator uses for Montana towns and a few places around the country, using 10 winters of data (2016-17 through 2025-26), November 1 through the end of February.

Montana gets far more chill than anything we sell needs, and October and March add hundreds of hours on top of these. Where chill really matters is mild-winter country, like the Central Valley of California, Texas, the Deep South and the low desert.

Why chill matters, even here

How we got these numbers

We checked every plant against university and extension guides, peer-reviewed dormancy studies, breeding programs and nurseries that publish chill figures. When good sources agreed, that's the number. When they disagreed, we weighed them and showed the full spread as the range. When no one had published anything for a variety, which is true of most hardy prairie, Russian and local Montana selections, we estimated it from its parents, its species and where it comes from, and marked it as our estimate. We never made up a number to look precise.

One thing worth knowing: lab tests on cut shoots usually come out higher than the field figures nurseries publish. The same 1991 study that put McIntosh at 1,086 put Dorsett Golden, an apple that grows normally on about 400 to 450 hours, at 814. So we use lab results to rank varieties against each other, and show the grower-scale number. Every source, every conflict and every judgment call is on our research page, along with a downloadable spreadsheet.

Common questions

Does Montana ever come up short on chill?

No. Our towns average 2,400 to 2,800 hours at or below 45°F from November through February alone, and even the mildest of the last 10 winters gave close to 2,000. The highest figure on this list is Ben Lomond black currant at about 2,000 hours, and October and March cover the rest easily.

Why are your numbers different from other nurseries'?

A lot of catalogs paste one chill range onto every variety they sell, and some numbers get copied from site to site. We tracked each figure back to where it came from, flagged the generic ones, and weighed lab studies against field experience. Where sources disagree, we show the range instead of hiding it.

What happens if a tree doesn't get enough chill?

Leaves and flowers come out late, slowly and unevenly. Bloom can stretch over weeks, so pollenizers don't line up, fruit set drops, and the tree gets weaker over time. It usually won't kill the tree outright, but it won't crop well.

Can a tree get too much chill?

No. Extra chill doesn't hurt. Once the requirement is met, the tree just waits for warmth.

Do seedlings need the same chill as the parent?

Close, but not exactly. Each seedling is genetically different, so we give seedlings the parent's figure with a wider range, and we never mark a seedling as well documented.

How accurate is the calculator?

It uses PRISM daily highs and lows, gridded at about 2.5 miles and adjusted for elevation, and estimates the hourly curve from them. In our checks against hourly records it came within a few percent on the at-or-below-45°F count. Your own yard can still differ: frost pockets run colder, and south walls and pavement run warmer. It covers the lower 48 states.

Can you help me pick?

Yes. Try our We Pick Your Trees form and we'll match trees to your site, winters and taste.

Climate data: PRISM Climate Group, Oregon State University, served through the NOAA Regional Climate Centers' ACIS web services. Chill figures compiled by Montana Fruit Trees, October 2026. If you grow one of these plants somewhere with mild winters and see something different, tell us. Real-world reports make this list better.