Question
Hello,
can I pollinate my pistachio tree artificially?My tree bears nuts that are empty.The trees are 10+ years old.
Thanks

Answer
Pistachio trees are either male or female.  It sounds like you only have female trees and no males.  Pistachios are wind pollinated so it sounds like you do not have any nearby trees that are blowing pollen to your trees.

You can plant a male tree, but it may be several years before it produces pollen.  Peters and Randy are names of male cultivars that are most common.  You may have a supplier in your area or can probably find one on the internet.

Another option is to observe your trees for when the begin flowering.  If you know where other pistachios are in your area, you could visit those trees and collect pollen from the male flowers.  To do this, you can put the male flowers in a paper bag (lunch sized) and tap the bag/flowers against your hand.  You should observe pollen collecting in the bottom of the bag.  It is best to collect pollen from several different flowers and several trees to increase the liklihood of collecting good pollen.  It is best to do the collection in late morning when the dew has dried, and lots of pollen is present.  You then take the pollen and sprinkle it onto the female flowers of your trees.  This is kind of tedious, but would be the most rapid way to get nuts.

Lastly, you may want to have a look at this presentation (http://fruitsandnuts.ucdavis.edu/files/74174.pdf).  It has some good pictures of male and female flowers so you can tell the trees apart.  Much of the information may be unnecessary for your purposes, but the images might be useful.

Good luck!