Print Friendly, PDF & Email

Do you dream about apple trees laden with fruit, a freezer stocked with home-grown blueberries and frozen pomegranate juice, or cherry pies baked with cherries picked off the tree in your backyard? When the new seed catalogs arrive, do you stare longingly at the pears and figs and think about whether they belong in your front yard or if you should start an orchard? If so, you’ve probably seen the phrase “chill hours” buried in the description.

At its simplest, chill hours, also known as chilling units or chilling hours, measure the hours with temperatures below 45 ⁰F. Another measure uses hours between 32 and 45 ⁰F. The Utah Chill Unit Model and Dynamic Model are both more accurate and more complex.

Think about chill hours in terms of dormancy. During the first stage (acclimation), you’ve already harvested your crop and fall is setting in. Winter arrives just as your trees enter endo-dormancy. During this phase, it racks up chill hours. After it receives enough chill hours, it enters eco-dormancy and breaks bud. As temperatures rise above 40 ⁰F, it starts a new tally: growing-degree days. Once it’s received enough chill hours and enough growing-degree days, it assumes spring’s arrived and starts growing.

The good news is that until your tree receives the necessary chill hours, it won’t bud out. That’s also the bad news.

If you plant cherry trees in Florida, they’ll grow. The low chill varieties might produce a few cherries. Just don’t get your heart set on pounds of cherries picked from the cherry tree you’ve lovingly tended for the last five years. The same applies to growing oranges in Wisconsin. It goes double for the pistachio tree I’ve always wanted.

Find out your chill hours before ordering any fruit or nut trees and, preferably, before planning your orchard.

Finding Your Chill Hours

Call your county extension office. They’ll know the average chill hours for your area and may already have a list of recommended varieties with a proven local track record.

Another option is AgroClimate’s Chill Hours Calculator. Enter your zip code and set the chill hours model to 32-45 ⁰F. Then set the end date for the projected period to a year. (For instance, start 10/01/2018 and end 09/30/2019.) Under graph options, click display historical average and display last season. Now, select the USDA research station nearest you from the map and open the Total Accumulated and Projected tab.

Do you mind a little risk? Do you want the earliest possible fruit even if it means misting your precious apple blossoms with water at 5 AM to protect them from frost? Having done this, I don’t recommend the before sunrise (and morning coffee) water hose routine.

If you don’t mind installing an overhead sprinkler system or waking up before the rooster, choose 90% probability from your state’s Freeze/Frost Occurrence Data sheet. Otherwise, go with 50% or 10%. (The lower the probability, the lower the frost risk.) Scroll down until you find the nearest city to your location and note the frost date.

Now, find your frost date on graph. The green cone shows the estimated minimum and maximum chill hours. Mouse over the top and bottom green line for these numbers.

A large grower may select multiple varieties so his orchards produce even during low-chill and high-chill years. You see this a lot with peach farmers because even 100 chill hours plus or minus the ideal growing condition can impact yields. Gardeners and market farmers should focus on the bottom. Select varieties that need a few hundred chill hours less than your available chill. That way they’ll produce during even during uncommonly warm years. Then narrow them down based on whether they flower early, mid-season, or late. Ideally, you want them to bloom after your frost date.

A Real World Example

My childhood neighbor retired from farming and took up apple growing. He grew Anna’s, Dorset Golds, horse apples, and Fujis. Every spring, he gripped because his low-chill Annas and Dorsets always bloomed before the first frost. He spent many hours outside in the cold with a water hose. That region of Georgia receives about 400-600 chill hours every year. Anna apples flower extremely early and need less than 300 chill hours. His liked to bloom in February. Most years, his Anna and Dorset Gold trees produced gorgeous blooms and frost killed the apples before they grew. His prized Fuji apples featured in many an apple cake.


Anna (apple). (2018). In Wikipedia. Retrieved from

Chill Hours Calculator – AgroClimate. (n.d.). Retrieved October 23, 2018, from

Chilling accumulation: its importance and estimation. (n.d.). Retrieved October 24, 2018, from

Chilling Hours / First and Last Frost | Weather. (n.d.). Retrieved October 24, 2018, from

Leave a Reply

Notify of

Oh, we are all about…

  • Cheer Up KitCheer Up Kit
    by Dee Dee Know somebody who is feeling a little …

Creating Shapely Legs

With the trend toward leggings and skin-tight jeans, having shapely legs is even more critical than ever. Getting your legs in shape is a task that requires more than one strategy, particularly if you haven’t made an effort before now. For the best results, you should use as many of the following tips as you can to tone and beautify your legs.

Eat Well

One essential component of encouraging your legs to look their best is to eat nutritious food filled with vitamins and minerals. Not only does this strategy provide your legs with the nutrition they need to look healthy, but it also helps to keep your legs thin and shapely.


Unless you hydrate your body adequately each day, your skin can suffer the kind of damage that leads you to creases, wrinkles, and discoloration. While some of these skin issues are going to develop anyway as you age, hydrating can help to slow down this process.


Keeping your legs feeling soft and looking smooth could be as simple as using specialized beauty products designed to help your skin retain moisture. Leg creams, lotions, gels, and butters offer rich moisturizing ingredients that enhance the natural beauty of your skin. Using one of these products once a day can make all of the difference between rough, scaly legs and smooth, attractive ones.


Whether or not you are a sun worshiper, you should use a protective lotion or cream that safeguards your skin against the harshness of the sun’s rays. Not only does this strategy help to prevent unwanted wrinkles and early aging, but it can also protect you against skin cancer. In addition to sunscreen lotions and creams, you can use cosmetics, soaps, and lotions offering protection against the sun’s rays.


If your legs look somewhat thicker than you would like, you might want to incorporate toning exercises into your routine. For the best results, you should include split squats, chair squats, leg lifts, and lunges.

If you want beautiful legs, it is up to you to do something about it. Take the time to create a beauty routine that you can follow on a daily basis to promote healthier, softer, slimmer looking legs. If you want to achieve exceptional results, you should approach this task from all angles, including nutrition, exercise, and skin care.

Picked For You

  • DIY Manicure: How to Create Newspaper NailsDIY Manicure: How to Create Newspaper Nails
    While your nails are still wet from the alcohol, press a strip of newspaper onto your nail. For this step you can either use a section from a full newspaper page or cut a page