Growing Marigolds from Seed and Cross Pollination

How can I prevent my marigolds from cross pollinating with other marigolds of different varieties?  I want to harvest seeds that will grow and look just like their parents.  My yard is really small, so each of my marigolds (they…

Italian plum tree not bearing fruit

I planted an Italian plum tree 5 years ago.  It is now around 12 ft tall and flowers every year but bears no fruit. I think I need another plum tree to pollinate it, but do not know the variety.…