Is it dependent upon what you are growing??

I guess this questions is one of those that are to hard to explain.

Very dependent upon what you wish to grow. First learn the difference between heirloom and open pollinated. Heirlooms are open pollinated but are a special subset. They are not commercial varieties. Beans (Phaseolus vulgaris) English peas ( Pisum sativus) are all open pollinated and do not cross easily. On the other hand Cucurbits ( squash, cucumbers, melons etc) cross readily and must either be isolated or bagged and hand pollinated to save seeds. Others cross but can be handled with isolation. Read a book on seed saving or Hang out in the seed saving forum for a while http://forums.gardenweb.com/forums/seedsave/

Here is a link that might be useful: seed saving forum

Yeah I have and I have learned a lot. I have read quite a bit also always to be a little more confused. I knew that cucubrits could cross up to half a mile. I know that most tomatoes will not cross excluding currant or potato leaf types. I figured that about beans and peas but to be honest I wasn't for sure.

What about heirloom flowers?? Will each variety cross or will it be less likely being an heirloom take for instance foxglove.

I know regular flowers will cross. I know that hybrids will never be true.

Is there something special about heirloom flowers that keep them from crossing?? Or is this just me wishful thinking and misreading??

Just take for instance I am planning on growing hellebore niger and hellebore orientalis from seed. I was curious to learn more about the plants. Well while reading I found out that the likely hood of them crossing is slim to none. Now I am not for sure if it is because they have bloom differences or if it is something because they are heirloom. Some say the niger will bloom, dependent upon your zone, the same time that the orientalis will. So that makes me think it has something to do with the "heirloom" aspect.

Take off your hat rub your head and tell me, am I way off on my thinking here?? :D

Has nothing to do with "heirloom" and everything to do with species. Any insect pollinated species will cross. Wind pollinated species less so. Some species are self pollinating and rarely ever cross naturally. Only plants within a species will cross in nature, altho techniques have been invented to develop some inter species crosses. Hybrids are nothing more than a controlled cross, mostly within species.

Ok, thank you so that means I was way off on my thinking concept. That does make a little more sense to me. I truly believe I have been wishful thinking. Oh well I still have a lot to learn!!