The easiest way is to bag the buds with nylon or cheesecloth prior to the flower opening.

However, if you want to completely prevent cross-pollination, seed producers state that individual varieties should be grown at least 500 yards apart (or is it 500 M?).

If you are saving the seed for personal use, then it isn't too big a deal, as most seeds will grow true because tomatoes have perfect flowers. Most studies estimate the rate of cross pollination due to insects is between 5-30%.
So worse case scenario is that 70% of your seed will grow true.
If you bag, less than 5% is achievable even when different varieties are grown right next to each other, and if 95 out of 100 seeds are true, that's good enough for me!
-CC

I agree with the above post. I've always believed the only way to get "true" seeds is to bag the blossoms. I don't, so I always buy new tomato seed or trade for seeds from people who do bag.

I'm not even planting a veggie garden this year because of the drought. Boo Hoo... I'm on a water well and I figure I will need all the water I can save for my tropicals. I will plant some habaneros in the flower beds. Please God, let it rain! And rain, and rain, and rain...

Formerly Hot Pepper Dad -- I LOVE your new name. It describes me to a T. I really crave capsaicin and can't go a meal without a habanero!

I've been growing and saving tomato seed since about 1984. The only time I've had any noticeable crossing has been when I planted things all together. Now, with standard varieties I plant in blocks of at least 4, give them at least 15 feet distance between varieties, and try to grow a block of pole beans (or something tall) between them. This has worked well for me. I give beefsteak varieties about 20-30' distance isolation, because they are more prone to crossing. Cherries, especially currant tomatoes; well, I usually don't plant them in the garden. I put them in a nitch somewhere across the yard on the other side of the house. They are the most prone to crossing.

Pay attention to bumble bees. They are the worst culprits I've encountered in tomato cross pollination. If you have a lot of them you should increase distance (or as mentioned above, which obviously would work best of all, bag flowers).

Drop me an e-mail if you'd like a copy of the guide I wrote on saving tomato seed. It's not professional, but it deals with a number of questions and practices.

George
Tahlequah, OK
kg8da(at)juno.com

Thanks all.

Bumble bees are something I see a lot of. Guess I spread them out and see how it goes :-).

randy

Another thing to consider, if you don't have the space, and don't want to bag flowers, is to take measures to save seed from *some* of the varieties. Most likely, your seed packets have several years' worth of seed and will keep for several years. So, you can save seed from varieties in rotation. This is just another idea.

George
Tahlequah, OK