Post edited 5:00 pm – April 22, 2011 by Crab Apple

Keep similar plants separated but this will only be effective on VERY large plots.

Cover blossoms….. maybe on a few plants you intend to save seed from …… it could be done on SMALL scale.

Separate them by pollination times…. using days to harvest to guestimate pollination times (85 days to harvest will pollinate before 120 days to harvest varieties)

This link was for preventing cross pollination in corn.

http://www.extension.org/pages…..-varieties

about tomatoes ( this only pertains to those you will save seed from)

http://www.selectedplants.com/…..saving.htm

I want to save seed, how far apart do
I have to plant to avoid crosspollination?

There are three kinds of barriers to crosspollination:  genetic
barriers, physical barriers, and temporaral barriers.  First we’ll
cover how tomatoes are crosspollinated, then how to prevent crosspollination.

Tomatoes are natural self-pollinators that can be pollinated by just
about any form of vibration whether from wind, insects, or humans with
electric toothbrushes.  The flower structure is such that the stigma
is surrounded by the anther cone.  As the stigma extends, it may protrude
beyond the anther cone which makes it available for crosspollination. 
Under normal conditions, most tomatoes have a natural cross-pollination
rate of about 4%.  Under some conditions though, this can be much
higher.  There are some varieties developed since 1930 in which the
stigma always stays enclosed in the anther cup.  These varieties almost
never get crosspollinated.  Most heirloom varieties fall into the
category with partially extended stigmas and some have a split anther cup
which exposes the stigma.  Heirlooms as a rule are likely to crosspollinate
though at a low rate overall.

Tomatoes are a flowering plant in the nightshade family that produce
pollen but not nectar.  The pollen is collected by several species
of insects for its protein content.  You may have certain insect species
in one part of the country that are not present or are insignificant elsewhere. 
Honeybees for example will rarely visit tomato flowers because they favor
nectar producing flowers over pollen only flowers such as tomato. 
If heavy nectar and pollen producers are in bloom, tomatoes will rarely
be visited so the level of competing bloom has to be factored in. 
Distance between plants is important because most pollinators will fly
to a flower near the one they are leaving.  This results in insects
flying down a row of tomatoes instead of flying to another plant several
feet away.

Genetic barriers are rarely used by home gardeners.  This would
be something like a male sterile line that has to be crosspollinated to
set seed.  This is something a large seed company might do but rarely
the home grower.  Physical barriers such as bagging flowers, growing
in a greenhouse and manually pollinating the flowers, or separating the
plants by distances that reduce or prevent crosspollination are among the
options available to the homegrower.  A temporaral barrier is growing
a tomato plant in such a way that there are no other tomatoes in bloom
to cross with it.  This prevents unwanted crosspollination with a
minimum of effort.  If you grow a tomato indoors and plant it outside
so that it is blooming very early when no other tomatoes are blooming,
this is the kind of barrier you have established.

If your garden area does not permit planting tomatoes at least 1/2 mile
apart, then some level of crosspollination will occur.  Very few pollinators
will fly more than ½ mile so this is a fairly effective isolation
distance.  A key factor is that as distance increases, crosspollination
falls off very rapidly.  Since most gardeners have only a few hundred
square feet, distance is not going to be an effective measure.  Bagging
flowers is the best alternative.  If properly bagged, 100% selfpollination
is assured. 

You can also take the combination approach.  Plant
tomatoes at least 25 feet apart, preferrably 10 or more plants of the same
variety, with competing flowers in between and save seed only when low
levels of pollinators are present.  This will reduce crosspollination
to a minimum.

Which plants should I save seed from?

The best plants with the characteristics you desire to continue make
the best seed parents.  Carefully check that a variety is true to
type before designating as a seed parent.

How do I collect, ferment, and dry the seed?

Seed should be collected from tomatoes that have begun to turn from
green to ripe.  A tomato that is either too ripe or too green is difficult
to extract seed from.  There is a stage where the fruit is fully colored
but still slightly firm which works best for collecting seed.  I carry
a deep tray with a stack of clear plastic cups, a sharp knife,an old towel,
and a permanent marker to the garden.  Take one cup from the stack
and label it with the marker, then pick a tomato and slice the bottom off. 
Squeeze the top of the tomato over the cup kind of like milking a cow and
most of the seed and gel will be squirted into the cup.  DO NOT do
this over the tray, sometimes seed go flying like they are jet propelled
and could wind up in the wrong container!  Continue picking tomatoes,
slicing and squeezing until you have as many seed as desired.  Then
place the cup in the tray and if needed, wipe your hands off with the towel.

The tray should be placed where it won't be subject to strong winds
or rain but NOT inside your house unless you just happen to like the smell
of fermenting tomatoes.  I have a porch behind the house that is protected
on 3 sides and has a table to sit the trays on.  In my area, fruit
flies and other insects love to lay eggs in the cups of fermenting juice. 
I cover the cups with a stretched sheet of plastic wrap to exclude the
bugs.  A thick fungal mat will form on the surface of the pulp in
the cups.  Depending on temperature, the fermentation will be complete
in 3 to 14 days.  It is very important NOT to leave the seed in the
fermenting cups more than about 2 weeks because the seed lose viability! 
Once fermentation is complete, I use a clean fork to stir the pulp up then
fill the cup with water and pour whatever floats out on the ground. 
Repeat the fill with water, pour off floating material 3 or 4 times until
the seed are mostly clean.  Then pour the seed into a stainless strainer
and rinse thoroughly under running water while rubbing the seed to separate
bits of tomato flesh.  You can then put the seed in bleach water to
help reduce seedborne diseases.  The bleach water should be made with
1 part household bleach with 5 parts water.  Don't leave the seed
in this more than 2 or 3 minutes!  Pour the seed into a clean strainer
to eliminate the liquid, rinse thoroughly, and then dump the strainer onto
a LABELED paper plate.  Note that the bleach treatment can be skipped
if you prefer in which case just dump the cleaned seed from the first strainer
onto the plate.  The bleach treatment is very important if you want
to trade seed because it reduces significantly the transmission of seedborne
disease.

Tomato seed should be left on the paper plate for between 2 and 4 weeks
by which time they should be thoroughly dry.  During this time, they
should not be in a place that is accessible to mice and should not be exposed
to direct sun or temperature extremes.  The best seed quality comes
from drying temperatures between 70 and 85 degrees (20 to 30 C). 
I like to stir the seed 2 or 3 times over the first week to keep them from
clumping together.  This saves time later when individual seed are
needed for planting.

I'm a packrat, how can I store my seed for the long
term?

Tomato seed should be properly dried and then stored in a glass jar
or a sealed plastic container such as a ziploc type freezer bag or a plastic
bowl with lid.  Their viability declines as temperature and moisture
increase so they must be protected from extremes.  Seed can be stored
at room temperature for up to 10 years with high viability. I have some
seed that are 15 years old and have been stored at room temp. They still
give 50% viability today though they take up to 20 days to germinate. 
If you want to store them truly long term (more than 10 years) then you
might want to freeze them in a well sealed glass container. The moisture
content must be below 8% for freezer storage.  You can get pouches
of silica gel dessicant from pharmacies which can be included in the container
to absorb any excess moisture.  Plastic or glass vials with tight
sealing lids can be easily found on the internet and make excellent containers
for long term seed storage.

Will my tomato seed grow?  Testing for viability
and trueness to type.

Its always a good idea to test seed you have saved to see if an accidental
cross has occurred.  This would show up if for example, a potato leaf
plant had been pollinated by a regular leaf variety.  Knowing what
percentage of seed will germinate can also help to ensure the approximate
quantity of seedlings desired.  I start a sample of seed at least
2 weeks before main planting with 20 seed of each saved variety. 
The seedlings are counted to see how many germinated and then let grow
to the first leaf stage to check for crosses.  I also keep some of
these seedlings for extra early transplants.

Wow: 250 feet apart will result in some cross pollination? My fenced area is only 100ft long…anything planted outside it is deer fodder. I have 3 different types of tomatoes: will have to result to other methods for dealing with the deer

What company didn't send you the seed?

I hope I'm right on this but I'm pretty sure that seeds that you buy at stores are heirloom unless they specifically say 'hybrid'. I composted some squash last year and now, their seeds are already sprouting in my compost pile!! They were not labeled 'heirloom' nor were they labeled 'hybrid'.

great link, thanks