Winter chill period necessary for apples to set???

In the checkout line in Walmart yesterday the cashier commented on our good weather, myself stating I was ready for some real Iowa weather. The man in line directly behind me commented on our chance of no apples setting unless we should get 34 consecutive days of temps. under 25 degrees. I had never heard this. Normally this would be no problem in an Iowa winter, but having the ground without snow until about 2 weeks ago we certainly haven't had a good chill period as he mentioned.

Anyone know anything about this?

Depends on what type of apple trees you have . They all have different chill times. I'm in 8B and I actually get apples but my tree needs few chill hours.

Temperatures between 32ºF and 45ºF are counted as chill hours. Anything lower than 32ºF doesn't count. A certain number of chill hours are needed for a fruit tree to properly break dormancy. Each variety has its own requirement. Unless that need is met, the tree will weaken, be attacked by disease and eventually die. If a tree doesn't break dormancy properly, the flowers may be malformed.

There are probably as many ways of counting chill hours as there are universities. Warm spells subtract from the count. Contact your local CountyExtension agent to find out what your average is. Then look up the variety you bought to see if it's chill hour requirement will be met in your area. My local agent recommends sticking to varieties that need 100 fewer chill hours than our average.

On the other hand, you don't want fruit trees that require a very low number of chill hours for your area or the tree will break dormancy too soon, bloom and set fruit before all frost is over. While many trees may be able to withstand hard freezes in your area, fruit and flowers are generally frost tender and you will lose your crop.

A few cultivars of some plants have blossoms that can endure freezing: some of the Scottish varieties of black currant, notably. Black currant (or blackcurrant for any Brits reading this) needs 800-1600 chilling hours. Lingonberries can also, I believe, take freezes when in bloom and not lose the crop. It's not to be counted on for most fruiting plants, so low-chill varieties tend to break dormancy too early in high-chill areas and produce no crop.

In my part of Florida, late-bloomers that require low chill hours are the best, because although we get few hours (300 to 600, usually nearer 300), trees often break dormancy early and a late frost from a spingtime cold-air mass will blast the blossoms. Pecans leaf out very late and bloom later, and most need little chill -- they're grown commercially here, which is no surprise. I plan to try some late-blooming almond trees some day, although I suspect that fungal diseases might do them in, even with spraying.

Unless there is a major climate change, I don't think you have have to worry too much about chill hours for apples in Iowa. an untimely frost should be your greatest worry.

Thanks for your input everyone. This was a completely new idea to me. Very informative.

The cold is needed for particuliar species of fruit trees but you should be fine in Iowa. I think it's interesting to check out what various fruit trees require as far as cold weather goes. I grow a variety of fruit trees and each one has it's own cold requirement.

Cuckoo