What Are Chill Hours for Fruit Trees?

Before planting an orchard full of citrus fruit trees, or other fruiting trees, one of the most important things to consider is if the plant will do well in your climate. You’ll want to be sure of two things for best results with fruit or nut trees. The first is that you live within the recommended USDA Hardiness Zone, and the second is that where you live receives enough annual chill hours.

But have you ever wondered why some fruit trees fail to produce a good yield or even no fruit at all? The answer could lie in the concept of chill hours. So what are Chill Hours and how do they affect the yield of the fruit trees you want to plant? Keep reading to find out.

What Are Chill Hours?

Most fruit and nut trees, except for citrus trees, will require a certain amount of time when exposed to the cold to bud and produce fruit in the spring properly. Chill hours are any time the plant is exposed to temperatures under 45 degrees F. These don’t have to be consecutive, they just need to reach a total by the end of the winter season.

It’s also important to understand that research has shown that this cold-induced hormone suppression occurs between the temperatures of 45 and 50 degrees F, but will not occur in temperatures under 30 degrees F. So chilling hours would be difficult for an individual to track.

This requirement is going to vary widely for different varieties of fruit-bearing plants. Some fruit plants will require a total of 8000-10000, which will be a better fit for far Northern climates. Other trees like citrus and tropical fruits require fewer chill hours, closer to 500 or less, and will be better suited for the warmer Southern climates.

Why Are Chill Hours Important for Fruit Trees?

As previously mentioned, citrus fruit trees, including varieties like tangerine trees, kumquat trees, and dwarf citrus trees, don’t require many, if any, chill hours to produce fruit in the spring. So why do most fruit and nut trees require so much time in the cold?

During the fall and early winter, a tree will begin a dormancy phase which is brought on by the longer colder days. Scientists don’t fully understand exactly what the reaction is between the trees and the cold. However, during this phase, the tree will suppress its hormones within buds until the spring when conditions are right for growth.

A certain amount of time in this chilled dormancy phase is required, so they bloom correctly and on time when conditions are right in the spring. Without adequate chill hours, they can produce less, late, or even no fruit at all.

What Kind of Fruit Trees Need Chill Hours?

We know now that citrus fruit trees are not a plant that requires chill hours to produce crops in the spring. But there are plenty of plants that need at least some chilled temperatures to bear healthy new growth.

While the amount of chill hours vary, plants like apples, pears, and stone fruits like plums, nectarines, and apricots will require the highest number of chill hours, and because of this, they typically do well in colder northern climates. On the other hand, fruit varieties like persimmons, figs, and pomegranates require just a few chill hours, the least out of all fruit plants.

The amount needed for each of these plants is flexible and can change even from tree to tree in the same orchard. Apples are a great example where some varieties, like Gala, require 500 hours of cold, whereas Red Delicious needs much more cold exposure at 800 or more hours.

How to Track Chill Hours

While you could get out a pen and notebook and mark down every single day throughout the winter where your area meets chill hour requirements, that would be a ton of extra work and hassle. Tracking chill hours in your area is best left up to the professionals, and luckily there are plenty of charts and resources available online to help you better understand your climate zone.

Generally the further from the equator, the more chill hours happen within that dormancy period. So a place like Florida will get between 0-200 chill hours each year, whereas the Pacific Northwest area will get the largest number throughout winter ranging from 2000-3400 chill hours.

It’s important to note that these are averages, and any area will vary in the number of chill hours it gets yearly. So keep this in mind when you start deciding what trees are best for growing in your area.

Choosing The Right Fruit Trees

After you know the average number of chill hours in your area, you can move forward with picking out the best fruit trees for your climate. The best rule of thumb is to pick out fruit tree varieties that require the same number of chill hours or fewer, to accommodate for those years where chill hours vary from average. If you have the space, it’s also helpful to plant a wide variety of cultivars to offset the years where average chill hours are more or less than usual.

Some plant varieties that typically require little chill hours may do well in environments with slightly more chill hours than they call for, as they’ve become well-adapted to mild and cooler areas. These trees should also be compatible with your US Hardiness Zone.

Your local nursery or plant store should have great options of lemon trees for sale like eureka lemon trees that are curated for the area you’re in. Or, if you prefer the convenience of shopping from home, you also can special order fruit trees for sale online from outlets like Yarden and get the perfect variety for your climate and average chill hours.

Treat Your Fruit Trees the Right Way

You probably never thought that the cold half of the year is just as important for fruit and nut trees as the fruit-producing season. However, chill hours are an important and necessary factor in productive growth for many varieties of fruit trees. Taking the time to research your climate, average chill hours, and what fruit trees do well within your assigned climate and USDA Hardiness Zone will ensure you have the best producing orchard in your area.

By providing the necessary amount of chill hours required for a particular fruit tree, growers can ensure a bountiful harvest and increase the chances of success in their agricultural endeavors. So, whether you’re a farmer or a gardening enthusiast, knowing the importance of chill hours can help you cultivate a healthy and fruitful garden.