Have you ever heard the term chill hours but weren’t quite sure what it meant and if it was important for you to understand? Well if you are growing fruit trees or certain vegetables it’s probably something you need to know about.
What Are Chill Hours?
Chill hours or chilling units is the measurement of a plant’s exposure in hours to chilling temperatures ranging from 32°F to 45°F. Many trees and vegetables require a certain number of chill hours to develop properly and be productive.
Tree Chilling Hours Requirement Chart
| Crop | Chill Hours |
| Apples | 200 to1000 |
| Peach | 200 to 800 |
| Plum | 400 to 700 |
| Pear | 400 to 1100 |
| Pomegranate | 100 to 200 |
| Persimmon | 200 to 400 |
| Fig | 100 to 200 |
| Pecan | 300 to 500 |
| Citrus | 0 to 100 |
| Cherry | 1000+ |
| Almond | 250 to 500 |
| Apricot | 300-500 |
| Chestnut | 400 to 500 |
| Pistachio | 800 |
| Olive | 200 to 300 |
| Walnut | 500 to 700 |
Other Plant Chilling Hour Requirements Chart
| Crop | Chilling Hours |
| Blackberry | 200 to 600 |
| Blueberry | 150 to 1000 |
| Grape | 100 to 600 |
| Strawberry | 200 to 400 |
| Kiwi | 300 to 800 |
Many biennial plants such as carrots, cabbage, and celery also require chilling hours to flower the second year to produce seeds.
Some Seeds Also Require Chill Hours
When it comes to chill hours for seeds the process is known as cold stratification. Seeds of many trees, shrubs, and perennials require this process before they will germinate.
This process can be simulated by soaking the seeds for 1 to 2 hours, thoroughly draining the seeds, spreading them out on a paper towel, wrapping them in another paper towel, placing in a ziplock bag, and putting them in the refrigerator for the required amount of time (usually about a month).
How Do I Find The Chill Hours For My Area
The Midwestern Regional Climate Center Vegetation Impact Program has put together some good interactive maps that will help you determine the approximate chill hours for your area.
