Grow Notes - December

For Home Orchards

A cold winter day is a fine time to curl up with a hot drink and plan for next season. Think about how to build on successes, evaluate mistakes and challenges. Are you growing what’s adapted to your climate? Are you also experimenting with interesting new varieties and/or some that require special care?

Have a plan for containerized fruit in cold climates. If bringing the pots indoors is not an option, be prepared to protect the sides of the containers from freezing temperatures. Bales of straw or burlap bags of mulch on all sides and on the top of the containers is a simple way to protect your plants.

Consider this calculation: Beginning December 1, temperatures fall below 45°F at 8pm and stay below 45° until 6am the next morning. That is 10 chill hours. If this pattern persists through the month, at the end of the month 300 chill hours are registered in the tree’s bio-computer. The same pattern continuing through January would total 600 chill hours.

Chill alone is not enough to bring a tree into bloom; it must be followed by consistent warming during the day. A warm day here and a weekend there will not trigger bloom. Warm daytime temperatures with nighttime temperatures above 45° must occur for 14-21 days before most varieties will offer flowers.

Understanding chill at your site can help you select varieties and evaluate their performance. Determine whether your site tends to have significantly more or less chilling than the hours-below-45°F model predicts. Late fall and early winter temperatures in the 45-55° range add to chilling, while temperatures above 65° reduce chilling.


Fruit Tree Chilling Requirement

Photo: jujubes, taken 12/16/2003.

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