February 19, 2019

Chill Out, Peaches!

Yesterday I noticed the first peach blossoms of the season on one of my peach trees, and that got me thinking about the topic of "chill hours".  For today's blog I'll be talking mostly about peaches, but the concepts still apply to many other types of trees.

What are chill hours?

The simple answer is the amount of time that the outdoor temperature is above freezing but below 45* F, which is especially important for fruit and nut trees.

 What does that mean for my fruit trees?

For trees like peaches, which shed their leaves each fall, falling temperatures are one of the signals that winter is coming**.
But how does the peach tree know when spring is coming?  Experiencing a critical number of chill hours -- remember, that's above freezing, but below 45* F -- is a signal for the tree to wake up from its winter hibernation.  We call this "breaking dormancy" in the plant world.

**Kudos to you if you caught that Game of Thrones reference.

My poor peach tree thought it was spring yesterday.  Today it's in the 40's.

How many chill hours does my tree need?

It's important to purchase fruit and nut trees that are matched to the number of average chill hours in the area where you live.  You can usually get this information from your state or county extension agency's website, or from any good nursery in your area.

Planting a tree that requires fewer chill hours than your area typically gets means the tree may think winter is over before it actually is, therefore, it may bloom too soon, and those blossoms are likely to get frozen and damaged -- and if the blossoms freeze off, that means no peaches.
This is what's happening with one of my peach trees right now.  It got plenty of chill hours, so when the weather warmed up for a few days, it "thought" it was spring!

Conversely, if you plant a variety that requires more chill hours than it will get in your area, your tree will be "confused" and this confusion can result in other problems, like deformed fruit.

Here in Central Texas I have seen nurseries selling peach varieties requiring anywhere between 200-750 chill hours.

Texas A&M's guide for peaches categorizes peaches as low-chilling (150-400 hrs), medium-chilling (450-650 hrs), or high-chilling (700-1000 hrs).

Best peach varieties for Central Texas

Medium-chill varieties are going to be your best bet!  Personally I've had the best luck with "Texstar", and "La Feliciana", which need around 450 and 600 chill hours, respectively.  If you have the space, I recommend doing what I did.  Planting at least 2 varieties with different chilling requirements, because some years one tree will have the better harvest, and other years the other tree will.

If you're in the Austin area, I recommend avoiding low-chill varieties with names like "Florida", "Gulf", or "Tropic".

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