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Ask Extension: Will my apple trees cross-pollinate?

Spring flowers, Haralson apple

Q: I know apple trees require two cultivars to cross pollinate and produce fruit. However, my trees haven't produced apples even though they have bloomed prolifically. Are my trees compatible for cross-pollinating?

A: My friend, Jeanie in Montgomery, MN, is an avid, knowledgeable gardener with acres of land planted for bees.

Haralson apple, a 1922 U of MN release


She grows a selection of dwarf / semi-dwarf apple trees: Honeycrisp, Honeygold, Haralson, and Whitney crab. Her 4-year old trees have flowered very well the past two years, but haven't produced much in the way of fruit. She contacted me wondering about tree compatibility and their bloom time.

I went to the best resource: our U of MN fruit breeder and apple expert, Dr. Jim Luby. Here's what he had to say about cross pollination of apple trees:

I tell people not to worry about this in MN. We don't encounter issues in our breeding program as we do our pollinations every spring [in the research orchards].


Genetic cross compatibility and overlap in the time of flowering are the two big issues. Fortunately, all our apple cultivars are cross compatible. (FYI this includes Haralson and Honeycrisp, both UMN releases.) 

Pollinizer flowering time is the other important issue. In other locales with longer bloom
Released by the U of MN in 1991,
the Honeycrisp apple is the MN state fruit.
 
periods, some as long as a month, getting overlap between cultivars is an issue. For those regions there are a number of charts available online that show overlap but they usually include a few of the cultivars we grow here. 

Fortunately, our bloom season in Minnesota is so short (usually everything is compressed into a week or 10 days) that almost all our cultivars overlap at least partially.  Only Zestar! and Chestnut are quite early but they overlap with one another quite well and with the ornamental crabs in the landscape. As far as pollination of the Whitney crab,  no problems that I know of as long as there are other early cultivars like Zestar!, Chestnut or ornamental crabs that overlap in bloom.

So Jeanie, this means your apple cultivars are all compatible. However, they are still young as apple trees go. A dwarf tree will take 3-5 years to reach maturity and produce fruit. Semi-dwarf maybe 5-7 years. So keep planting for the bees and watering your trees, and I will bet you a bumper crop you'll have apples soon.

More on U of MN apples: 

Author: Julie Weisenhorn, Extension Educator, Horticulture



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