Never done it myself, but try
http://faq.gardenweb.com/faq/lists/tomato/2005025852004159.html

See "Using Physical Barriers to Prevent Cross-pollination"

Hope this helps!

I purchase tulle bags at the dollar store. They are cheaper than the ones in bridal or hobby shops.

reut8, thanks for the link. So if you are only saving seed for your own use and don't care that 2 to 5% of the seeds may be crosses you don't have to take any special precautions, but if you want to be certain of a pure strain you do. I wonder how many commercial companies and seed traders actually do have pure strains and take all the recommended precautions.
I know I have a few big black bumblebees that visit my tomato blossoms, but I'm glad they do because I read that production can be increased by 50% if tomatoes are insect pollinated, and the tomatoes will be bigger because they have more seeds in them because more pollen was deposited, size being directly related to number of seeds.

ruet

Yes, I read that before posting but it didn't give me the information I wanted.

xaroline

I'd be delighted if I could purchase blossom bags cheaply, but we have only one chain of Dollar Stores and they don't carry the tulle bags. I think I'm going to have to make them, so I hope someone who has made theirs can tell me the dimensions, fabric, etc.

So if you are only saving seed for your own use and don't care that 2 to 5% of the seeds may be crosses you don't have to take any special precautions, but if you want to be certain of a pure strain you do. I wonder how many commercial companies and seed traders actually do have pure strains and take all the recommended precautions.
I know I have a few big black bumblebees that visit my tomato blossoms, but I'm glad they do because I read that production can be increased by 50% if tomatoes are insect pollinated, and the tomatoes will be bigger because they have more seeds in them because more pollen was deposited, size being directly related to number of seeds.

****
I think the article in the FAQ here about how to prevent x pollination is an excellent one.

Seed Companies: Some do their own seed production, some subcontract out, some buy wholsale off the shelf and some do a combo of any of those tree methods of obtaining seed. And some who do their own seed production use adequate geographic isolation and others aren't able to.

I used to do a wrong varieties thread here and certain companies rose to the top in terms of the least amount of crossed seed.

Crossed seed is most prevalent amongst those who trade seeds.

Cross POllination; it can vary widely depending on where someone lives, the specific pollinators in the area, the weather and much more. It's Halictid bees, tiny sweat bees that do most of the X pollination where it exists.

For an excellent article on tomato cross pollination go to Southern Exposure Seed Company and look for the article by Dr. Jeff McCormack, who used to own SESE, about xpollination and the title is NCP, or natural cross pollination. I think some of Jeff's geographic isolation suggestions are far too conservative, but would be fine for a commercial enterprise, but it's the info about X pollination itself that is the worth of the article.

Californian, yes, those who grow tomatoes in greenhouses do often hire hives for the season, and yes, there can be more fruits, but fruit size is not neccessarily linked to the number of seeds in a fruit. Look at all the heart and paste varieties with so few seeds as an example. So visits by bees, and they aren't there for the nectar b'c tomato blossoms don't have any, they're there for the pollen as a protein source, can help ensure that more blossoms set fruit.

Self pollenization is usually about maybe 90%-95 % effective, but that depends on the variables that you can read about in that SESE article. Any ovules in the tomato ovary that aren't self pollenized can then be cross pollinated , again, depending on variables.

I've listed maybe 4-500 different varieties in the SSE Yearbooks over time and grown about 2500 hundred varieties to date, and of the ones lsited in the Yearbook I know od less than maybe 15 that were cross pollinated.

And I didn't even know about those until I'd distributed 100's of seeds for a single variety. And that's b'c it depends on how many fruits were processed for seed production. Never ever save seeds from jsut one fruit off one plant, save from several fruits off one plant, save several fruits from two plants, well, you get the picture.

What one accomplished by doing that is to dilute out any cross pollinated seeds, so that's why a person may not ASAP know that saved seeds from a variety do have some X pollinated seeds.

I do a free seed offer elsewhere each year, now closed, and alst year just one person got an off plant from one of the new varieties, and I'd distributed the same seeds to many who participated in that seed offer.

So, use blossom bags if you feel you need pure seed for a variety ( not a strain), depending on what you plan to do with those seeds. For many folks both hobyy gardeners and commercial folks who do their own seed production, way too many plants are grown, in the hundreds and thousands and bagging blossoms is just not practical, or possible.

Carolyn, not editing the above b'c some just stopped by to visit,

Anney -
Any lightweight material would work, such as row cover or coffee filters or cheap nylon tulle, and remove it when you see the tomato started.

Fold and staple a piece of it around the blossom cluster (use a strip big enough to take in the whole unopened cluster). Bees aren't likely to crawl past a barrier.

LG

My concern about removing the bag after the tomato forms is remembering which tomato I bagged! I'll have to do something to indicate which one to save the seeds from. So I wondered what others do. Make the bag large enough for the future mature tomato and leave it on until you harvest the tomato?

Though I plan to do a pretty good spacing for most of my OP tomatoes, some of them will necessarily have to be close, and I cannot shift them around so I think they wouldn't cross with an errant bee or other pollinator. So I figure for those I want to grow more of, I'll bag them.

I remove the bag when the tomatoes start to get too big for it or after the last flower fades inside, whichever comes first. I then tie a peice of ribbon or yarn around the truss that was bagged and forget about it until it is time to pick the fruit.

Just go to Hobby Lobby or other fabric store and purchase some nylon tulle, finest woven.

Can you sew? make a bag , any size you want.
Cannot sew? just take a pies, cover the branch, tie it down
loosely.
After the needed fruit(s) is formed, remove the bonnet and tag the fruit, let the fruit over ripen, pick it....

I make my own from a really massive roll of sheer fabric I got at an auction. Not sure exactly what fabric it is, but it works well. I don't make them pretty, just cut the fabric into a large rectangle, fold in half and sew up two sides with the machine to make a little bag. It takes less than 30 seconds to make a bag this way. I attach the bags over the blossoms by twisting green gardening wire or twist ties over the stem. I remove the bags when all of the blossoms on that stem have developed fruit, and then I mark that stem with the gardening wire that I previously used to hold the bag on.

There's been times I've been too lazy to set up the sewing maching and I've done the exact same thing using fabric glue. I can make a whole bunch of these while sitting down watching my favourite tv show. I was amazed that fabric glue stood up well to our tough weather conditions, so for those of you that don't sew, you might want to give it a try.

It's easy and cheap. I think I paid $15 bucks for the industrial sized roll of fabric at an auction and I make little baggies during the winter time.

Thanks to all for the suggestions!

hmacdona

My sewing machine is elsewhere, so your suggestion about fabric glue is much appreciated. I've never used it, but I imagine it would hold up pretty well since it ought to be waterproof.

I make my bags about a foot square and add a draw string to tie them onto the blossom branch. I usually buy a bolt of tulle from Michael's with a coupon.

Discovered the first year that attaching a string or ribbon to the branch just wasn't enough. I ended up picking fruit that had been bagged because the string was hidden in the foliage of the plant.

I now leave the bag in place until the fruit is ripe. Then there are no accidental harvests.

Cindy

cindy

So you estimate their mature size when you bag them so you can pick the right one. I'd wondered about that, too. I think I can keep the varieties separate if I carefully follow my planting plan, so the only remaining concern is identifying the bagged fruit, as you note.

I may do the same thing just to be on the safe side, at least for plants that I know will grow lushly.