North American Fruit Explorers mailing list at ibiblio

[John Bunker <john.p.bunker@gmail.com>]

I agree with Jim that most of what has been written in books (and there hasn't been much) about hybrid plum pollination is inaccurate or just copied from someone else.  However, there is some good stuff out there, including FA Waugh's Plums and Plum Culture, written in 1901.  I have read and re-read many times the Saskatchewan article to which Melissa refers.  I consider it to be the best attempt yet at an intelligent explanation of plum pollination.  

We have about 40 hybrid plum trees  on our farm in central Maine, including most - but not all- of the common ones and several that are more rare.  We grow them in clusters of 3-12 trees, with trees spaced about 3-6 feet apart.  Until we planted straight species (P. americana) we got fruit, but never had great crops.  Out best years have all been since the species have begun to flower.

This is still anecdotal evidence however.  This year in central Maine, many growers had huge crops, seemingly no matter what they did or didn't do.  And of course, in many areas there is the issue of plum curculio which may (or may not) play a key role in cropping.  

Some factors that may effect pollination include:

Unlike P. domestica and a number of other Prunus species, hybrids are thought to be not self-fruitful.  

Hybrid plums are obviously hybrids and as hybrids, they  have reduced amounts of viable pollen.  (Think mules.)

Hybrid plum varieties have differing flowering periods from one another, not always overlapping.

The timing of  what viable male pollen there is in hybrid plums does not necessarily correlate with female receptivity in neighboring trees. 

There are several different species combinations that fall under the banner of "hybrid plum".  Some of those combinations are known, some guessed at, some unknown.  Some even exhibit "European" type characteristics and/or susceptibilities. 

Superior is a plum with an odd history.  While the literature generally calls it: Burbank (P. salicina) x Kaga (P. americana x P. simonii), in the old catalogs (30+ years ago) I have seen Superior referred to as both a hybrid and a European. 

Unfortunately, breeders and nurseries pretty much gave up on hybrid plums decades ago, for what ever reason.  As such, a good deal of what's floating around may or may not even be correctly identified.  The best source of a variety is a grower who knows the fruit and has bearing trees.  That's one of the beauties of grafting your own.  If possible, I always "go to the tree" when I want to add to the collection.

With best regards,

John Bunker

Fedco

trees@fedcoseeds.com

www.fedcoseeds.com 

PO Box 520

Waterville ME 04903

207-873-7333

fax: 207-872-8317

 

On Nov 17, 2008, at 4:30 PM, Melissa Kacalanos wrote:

    We Americans tend to believe that anything

written in a book is truth whereas a published work

is no more than someone's (sometimes uneducated)

opinion.  Don't believe everything you read.

What's worse, this thing about hybrid plum pollination

is from something I read on the internet:

http://www.usask.ca/agriculture/plantsci/dom_fruit/articles/plums.pdf

It's by some academics at the University of

Saskatchewan, where I've never even been, so how do I

know Saskatchewan even exists?

Despite the anecdotal evidence from people on this

list who say their hybrid plums get pollinated just

fine, I'll probably play it safe and plant a pure

native plum anyway.

Perhaps since funding for hybrid plum pollination

studies in Saskatchewan is meager, the evidence in

this paper is somewhat anecdotal too, although it does

seem significant:

"Our recommendation regarding the necessity of  wild

plum pollinizers has been 

reinforced by our observations over time and in

several locations. 

 Many years ago our attention was drawn to a Pembina

plum tree growing at the residence 

of  Mr. and Mrs. Eric O. Bert.  The fruit yields on

this specimen were outstanding compared to 

other specimens of the same cultivar growing in the

city.  We assumed that there was something 

special about this tree and it was propagated.  The

young Pembina trees and trees of many other 

plum cultivars were planted in the university orchard

but their fruit yields were poor.  Dandy and 

Bounty had been planted as pollinizers in this

orchard. 

 In another location a 'multi-graft' plum tree

consisting of four hybrid plum cultivars and 

one Prunus salicina cultivar grafted together had been

producing poor to fair crops at the 

residence of one of the authors.  Assuming that these

cultivars were cross pollinating, the seeds 

from this tree were saved and grown into mature trees.

The objective was to find a superior 

selection among the seedlings.  When these seedlings

began to bear fruit, it was obvious that the 

pollen parent to at least 95% of them was a wild plum

and, therefore, a superior selection was not 

found.  Also, it was significant that this large group

of seedlings bore few fruit even though most 

of them were 75% wild.  There was no completely wild

plum near them.  

 Later it was discovered that a wild plum was growing

in a neighbour's yard approximately 

100 meters away from the original 'multi-graft' plum

tree. This was the pollen parent.  

 As a test of the of the pollinizing efficiency of

wild plum, a young specimen of Prunus 

nigra, wild plum, was planted near the 'multi-graft'

tree.  The year that this young wild plum tree 

began to flower marked the beginning of outstanding

fruit yields on the 'multi-graft' tree. 

 Having made the above observations, the Bert

residence was revisited to inspect the 

Pembina tree and to look for a wild plum that we

suspected was growing nearby.  There was a 

wild plum growing in the same yard.  It had not been

noticed on the first visit years ago. "

Melissa

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