simy1 said:

Now, my question: of the four trees, two fruit profusely, one fruits
little, and the best looking tree nearly does not fruit at all. I
googled it, but I wonder if there is something I need to be aware of
when I select my future trees this fall. They are not male-female, so
is there anything else that affects fruit production.


Mulberry trees can be monoecious or diecious. They can even change sex!
(Or, as the scientists have it, "Mulberry bears different sex types, i.e., male,
female and bisexual flowers on the same plant (monoecious) or on different
plants (dioecious), with expression of sex often depending on several
physiological and biochemical factors.")
http://www.biomedcentral.com/1471-2229/1/3

A 'rooster' tree will be larger and healthier looking because it only
produces pollinate catkins and isn't stressed by fruit production. Typically,
the mature male trees have leaves that are mostly not lobed, while female
trees have a full range of leaf shapes.

The neighbor cut down the large 'rooster' tree in his yard spring 2004 and
there was much rejoicing, as the mulberry crop was smaller. This year
two young trees in another neighbor's yard went male and the rotting
berries slicked the ground once again.

White mulberries are extremelly variable in taste and color when ripe.
(Some actually ripen white, some red, most purple or nearly black.)
If you really want to grow quality mulberries, wild seedlings would
not be the best route. Better to graft a known quality scion to a wild
rootstock, or buy a tree that's a named cultivar.

Everything I've read says the black mulberry (Morus nigra) is the
mulberry with the best flavor, but it's not hardy in Michigan.

Mulberries can make a nice jelly, even nicer when blended with some
raspberries or currants. Sometimes finicky to gel in the pure juice.

See also California Rare Fruit Growers article on mulberries:
http://www.crfg.org/pubs/ff/mulberry.html
--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)