Hopefully Remy may key in on this also.

Anything that is open pollinated will cross with each other. Hybrids will not be true though they may be similar to the parent plant. If I am not mistaken sweet pea is open pollinated.

You can save seeds from both the heirloom and the hybrid but do not expect true seeds from the hybrid if it produces seeds, some hybrids are sterile. The million dollar question is always how far apart does a plant have to be to not cross with another of the same genus. I do not know that answer, though I am always seeking to find that out.

It is really up to you, some actually save seeds from hybrids to see what kind of plant they may get. Though it may take several generations to get a stable strain. I think I read somewhere after 3 generations you may get a plant that produces true seed.

As far as the heirloom, chances of them crossing are great if you have them pretty close, but you can always save the seeds and grow a plant and just see what you get. It may work then again you may have produced your own little unique hybrid from them all. That is another million dollar question!!

Ay yie yie!

Maybe I could do a three legged tee pee with three different plants (say bean, morning glory, sweet pea) and continue like that, so when the bees go from one flower to the next, less chance of crossing? I thought sweet peas self pollinate before the flowers open? I'm confused.

Thanks for the input, Carolyn, if I had a million dollars I'd send it your way!!!

Carolyn,
So nice that you think I might know the answer. I'm not positive about Lathyrus odoratus(Sweet Peas.)
I can tell you this. What you wrote is not entirely correct not anything that is OP(Open Pollinated) will cross. Some things(lettuce, tomatoes, some members of the bean family, etc.) are designed to be a bit more difficult to cross. Edible Peas(Pisum Sativum) for example are pollinated before opening.(I think this where the confusion from GardenUnusual is occurring) The same goes for some beans. Often times crosses will occur because bees rip open blossoms looking for the pollen or nectar. I am a firm believer that you should grow a good variety of plants with attractive blossoms to get the bees attention. They will go for the easy food. I've watched them bypass my tomato blossoms(which in general are also self-pollinating and have a low crossing rate, but bees sometimes do get at them before pollination occurs.) for other flowering plants.
With all that said, there are a few members of the Bean family that bees do cross pollinate at a fairly regular rate. I'm not sure if Lathyrus odoratus is one of them or not.

GardenUnusual,
Your idea of growing other thing is spot on. Trying to have a s much distance(placing the tee pees in separate garden areas if you can) as you can obviously helps too.
Remy

Thank you, Remy.

Would there be a recommended book for seed saving?

Cheers

GardenUnusual,
For vegetables, I definitely recommend "Seed to Seed" by Suzanne Ashworth. It has lots of good info if you vegetable garden.
For flowers, I do not know of a good resource, there are some online, but they are limited. Of course the problem is the world of flowers is too vast. Vegetables have a set amount of Genuses that we grow. A book even to cover the main flowers we grow would be a major undertaking. I've had a few friends say I should write one, and I find this quite amusing. For all I know, there is still so much I don't know.
For now the best option really is to search here and the web, and when there's no answer, ask : )
Remy

many thanks, Remy.

Well Remy, I have learned an extremely lot from you, so of course I think you would know the answer, lol.

See I never even considered the relation to a bean plant and sweet peas, but it makes sense!!