Chillin' in NC part 2

The warm weather continues in NC, articles are appearing in newspapers and we have yet to see a snowflake. And many folks are asking what is happening to the plants and in particular, will they have enough chilling hours this winter to grow normally in the 2012 season.

In the Jan 10th post I discussed chilling hours. Since then, I have been asked by a few folks, what the required number of chilling hours are for different fruit. Here is a table that I use for class. Please note that these are general number of chilling hours and within each type of fruit crop, there are large differences among cultivars.

In general, inadequate chilling would result in low vigor and low productivity.

Grape (vinifera)	100-400
Grape (labrusca)	1200-1400
Strawberry	200-300
Blueberry (Rabbiteye)	200-500
Blueberry (Highbush)	650-850
Blackberry (Thorny)	200-600
Blackberry (Thornless)	700-1100
Raspberry	800-1700
Cranberry	2000

In general, these are the conditions that are used to measure chilling hours:

• Period of cold temperature during the winter to induce dormancy and promote satisfactory shoot and fruit development
• Temperatures most effective: 37-55°F
• Most commonly used for calculation 32 and 45 ° F
• Freezing temperatures are ineffectual
• Temperatures above 59 ° F will reverse chilling accumulation

But each crop has its own model, including blackberry. That will be the topic of the next post.