Pick up know-how for tackling diseases, pests and weeds.
Farm bill, farm marketing, agribusiness webinars, & farm policy.
Find tactics for healthy livestock and sound forages.
Scheduling and methods of irrigation.
Explore our Extension locations around the state.
Commercial row crop production in Arkansas.
Agriculture weed management resources.
Use virtual and real tools to improve critical calculations for farms and ranches.
Learn to ID forages and more.
Explore our research locations around the state.
Get the latest research results from our county agents.
Our programs include aquaculture, diagnostics, and energy conservation.
Keep our food, fiber and fuel supplies safe from disaster.
Private, Commercial & Non-commercial training and education.
Specialty crops including turfgrass, vegetables, fruits, and ornamentals.
Find educational resources and get youth engaged in agriculture.
Gaining garden smarts and sharing skills.
Timely tips for the Arkansas home gardener.
Creating beauty in and around the home.
Maintenance calendar, and best practices.
Coaxing the best produce from asparagus to zucchini.
What’s wrong with my plants? The clinic can help.
Featured trees, vines, shrubs and flowers.
Ask our experts plant, animal, or insect questions.
Enjoying the sweet fruits of your labor.
Herbs, native plants, & reference desk QA.
Growing together from youth to maturity.
Crapemyrtles, hydrangeas, hort glossary, and weed ID databases.
Get beekeeping, honey production, and class information.
Grow a pollinator-friendly garden.
Schedule these timely events on your gardening calendar.
Equipping individuals to lead organizations, communities, and regions.
Guiding communities and regions toward vibrant and sustainable futures.
Guiding entrepreneurs from concept to profit.
Position your business to compete for government contracts.
Find trends, opportunities and impacts.
Providing unbiased information to enable educated votes on critical issues.
Increase your knowledge of public issues & get involved.
Research-based connection to government and policy issues.
Support Arkansas local food initiatives.
Read about our efforts.
Preparing for and recovering from disasters.
Licensing for forestry and wildlife professionals.
Preserving water quality and quantity.
Cleaner air for healthier living.
Firewood & bioenergy resources.
Managing a complex forest ecosystem.
Read about nature across Arkansas and the U.S.
Learn to manage wildlife on your land.
Soil quality and its use here in Arkansas.
Learn to ID unwanted plant and animal visitors.
Timely updates from our specialists.
Eating right and staying healthy.
Ensuring safe meals.
Take charge of your well-being.
Cooking with Arkansas foods.
Making the most of your money.
Making sound choices for families and ourselves.
Nurturing our future.
Get tips for food, fitness, finance, and more!
Understanding aging and its effects.
Giving back to the community.
Managing safely when disaster strikes.
Listen to our latest episode!
Fruit crops vary in the amount of cold winter temperatures they require during dormancy in order to break bud and flower in the spring. The number of hours temperatures are below 45 °F and above 32° F are considered 'chilling hours'. Generally chilling hours are calculated starting after the first frost. We will report chilling hours from Nov 1st through the end of February for several locations across AR.
Chilling hours are the number of hours a plant has spent below a certain temperature during the dormant period.
Chilling hours are important because they regulate the plant's ability to 'wake-up' after their dormant period in winter. During the cold dormant period the plant essentially accumulates signals within their tissues that indicate when it is time to 'wake up' based on how many hours the plant has spent below a certain temperature. More hours spent at a certain range of col temperatures, equals more signals.
Different crops require a different amount of these signals before they are ready to break dormancy. Once the required number of signals is reached and temperatures warm, an alarm goes off within the plant telling it to wake itself up!
The rate of accumulation of these signals within the plant varies based on temperature. The ideal temperature for plants to accumulate chilling hours is 45°F, but it is generally assumed that temperatures between 35-45°F provide good chilling hour accumulation. At temperatures below 35°F, generally no chilling is accumulated.
Some models assign different rates of chilling hour accumulation to different temperatures. Some models deduct chilling hours when temperatures go over 60°F. The Utah model is the standard model used for fruit crops.
Once the adequate number of chilling hours has been reached and temperatures warm the plant will be ready to break dormancy and buds will begin to grow and the plant will flower. For this reason it is important to choose varieties that have similar chilling requirements as what is received at your location. This will ensure in most years adequate chilling is achieved and that plants do not come out of dormancy before the winter is over.
Cold damage to emerged buds is common when low chill varieties are planted in an area that receives medium to high chilling hours on average.
For example: A peach variety with a 200 hour chilling requirement planted in a place with 700 average chilling hours is likely to break bud once the 200 hours have been met and if an un-seasonal warm spell occurs. However there is still likely to be 500 more hours of cold temperatures for that location! This peach variety is likely to experience cold damage to blooms in most years.
Serious impacts to plant growth occur when insufficient chilling hours are accumulated during the dormant period.
Symptoms of Lack of Chilling Hours:
Average chilling hour accumulation has fluctuated drastically in recent years from previous standards. For this reason we plan to post the number of chilling hours accumulated here for each year. More locations will be added as we are able to access that data.
Average Chilling Hours Accumulated by March 1st for Major Locations in AR from 1990-2000*:
U of A Campus, Fayetteville- 1,024
Fruit Research Station, Clarksville- 1,081
Southwest Research Station, Hope- 901
Wynne, AR- 1,069
*Source: Vance, L and C. Rom. Chill and Heat Accumulation at Four Sites in AR, 1990-2000. Horticultural Studies. AAES Research Series 494. (Calculations were based on the Utah model)
For Selected Reporting Period
56.5
*Average high and low temperature data were collected from: https://www.weather.gov/wrh/climate?wfo=shv
**Chilling hours for Hope, AR were calculated using the chill hours app developed by Mississippi State University Extension. The chilling hours app can be found here.
Check the Arkansas Chilling Hour Reports Archive to view past years reports (2017-2021).
Chill Model=Calculated using max temp of 45F and min temp of 32F, 1 unit is accumulated per each 1 hour between these two temperatures
Utah Model=
1 hour below 34°F = 0.0 chill unit
1 hour 35 - 36°F = 0.5 chill units
1 hour 37 - 48°F = 1.0 chill units
1 hour 49 - 54°F = 0.5 chill units
1 hour 55 - 60°F = 0.0 chill units
1 hour 61 - 65°F = -0.5 chill units
1 hour >65°F = -1.0 chill units
Source: Richardson, E. A., Seeley, S. D., Walker, D. R., Anderson, G. L. And Ashcroft, G. L. (1975) Pheno-climatography of spring peach bud development. HortSci. 10: 236-237.