Gary,

It might be too early in the season to pick most varities of plums. Maybe a
gardner can tell us. In austin.food, "Wooly" said he bought some plums at a
roadside stand near Fredericksburg. They might be an early variety, or they
might be shipped in to augment the stand's produce.

IMHO jam/jelly made from sweet eating plums can lack flavor. I like jam made
from the wild sand plum/Oklahoma plum/sour plum:

http://aggie-horticulture.tamu.edu/o...unusgracil.htm

Sand plums are small, only a bit larger than grapes. They don't grow in
Central Texas. I think it would be worth while to locate a source if you
are going to the troube to make homemade plum jelly. You have time as they
will not be ripe until about August.

jjhnsn