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Maximize your almond dormancy period

Chill out, almonds

3 Min Read
Submitted by Wilbur Ellis

As the weather starts to chill, so do almond trees.

Almonds and other perennials with a dormancy period must fulfill a chill requirement – a much-needed, good night of sleep for trees.

“A good chilling period is like REM sleep,” said Patrick Troy, field development specialist at Wilbur-Ellis Agribusiness. “We all know from the human perspective, if you don't get a good night's sleep, then your performance suffers the next day.”


As a tree drops leaves and ceases photosynthesis, it must have energy stored in a carbohydrate sink for the next season. Buds form in the fall, but need energy and a sufficient dormant period to develop. Without sufficient chill, trees will not wake up on time or bloom uniformly.

The ideal temperature for chilling ranges somewhere between 32 and 54 degrees Fahrenheit.

“The Cinderella-story perfect match is around 45 degrees,” Troy said. “You want it to get cold at night but have some warmth during the day. Like sap in the Vermont spring, this sweet spot provides movement in the veins, xylem and phloem of the trees.”

Josie Hugie, Wilbur-Ellis branded technologies research data manager, explained the difference between counting chill hours and chill portions, noting that almonds have a chilling requirement of 200-300 hours.

“Chill portions have a graduated scale based on the actual temperature above or below 45 degrees,” said Hugie. “Chill hours only count up to 45 degrees. Below 44 degrees, your chill hours are going to be the same as chill hours at 35 degrees. But you'll get more chill portions if you’re closer to 45 degrees than to 32 degrees. It’s a more accurate measure of almond chilling, and better estimates the effects of warm temperatures.”

Every hour is important. The industry responded and now uses chill portions as the standard measurement to better calculate the effects of temperature fluctuations.

Extreme hot and extreme cold alike shock almond trees out of their “REM sleep” state of dormancy. Almond growers can’t change the temperatures their trees face, but there are other considerations to improve chill.


Tips for Better Chill

Winter chill is one of the limiting factors in yield potential. With unpredictable weather, what can growers do to increase yield?

A product such as Diffusion reflects light and protects almond trees from heat without interfering with photosynthesis. It consistently increases chill time by 3%-4%, according to Hugie’s research.

Improving yield also starts with ensuring the plant is healthy and robust while it’s photosynthesizing, Troy said. Optimizing fertility before leaves drop is critical. Management practices such as minimizing salt in the soil, adequate irrigation, pruning and tackling disease issues are also important to consider.

Modeling may be an option too. The University of California-Davis Carbohydrate Observatory analyzes carbohydrates to simulate what is happening with the sugars and starches in trees and created a predictive model for yield and environmental stressors, including chill time.

“It’s not going to get easier to be a grower. So those old tools of just saying, ‘Did it rain enough? Was the winter cold enough?’ You can't change that. You can record it, but these modeling systems are going to help us better predict it,” Troy said. “Employing practices and products that reduce variability will safeguard quality and yields for the grower. The focus has to be on a return on investment for each input.”


The clock hasn’t struck midnight yet. Even though nuts are harvested, the trees are out there with one last opportunity for a foliar feed and irrigation. Then, it’s lights out. The plants will go to sleep with all reserves and possibilities for a good year stored within.

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