Tomatoes and cross-pollination?

gamebirdMarch 7, 2009

In talking to my father about the different varieties of tomatoes I'll be planting this year (thanks Dawn!), he said I should separate all the plants or else they'd cross pollinate. I didn't know tomatoes were prone to cross-pollination. Are they? If so, how far apart should they be?

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helenh(z6 SW MO)

If you want to save the seeds, you can put fine mesh bags over the flowers to prevent cross pollination and mark those tomatoes. Some suggest wedding sachet bags. You can take the bags off and use them again after the flower is pollinated. I have not done this read about it in Carolyn Male's book. Also most tomatoes do self pollinate but there is a chance of cross pollination. The current tomatoes are more likely to cross pollinate. The tomato forum has this info explained better.

    Bookmark   March 8, 2009 at 12:26AM
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Gamebird, I sent you an e-mail with a guide, which talks about isolation distances. Back in the early 80s, when I first started growing numbers of tomato varieties, I didn't protect my plants at all, and I grew them all together. I did have significant crossing. But since I started planting them in their own little blocks (all of one kind) with some isolation distance, I haven't noticed any crossing.

Helen's suggestion about mesh bags might be the way to go, if you don't mind doing it. That way you could grow them together and still get some seed. I've never done that.

Current tomatoes, and some of the cherries are very prone to crossing. Some of the large beefsteaks are rather prone as well.

Tahlequah, OK

    Bookmark   March 8, 2009 at 7:11AM
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Okiedawn OK Zone 7


If you are not going to save seed, cross-pollination will not be an issue. The act of cross-pollination will not affect the fruit you pick and eat this year.

If you are going to save seed, you either should bag blossoms, and then tag or mark that fruit so you'll know at harvest time which fruit to save seed from, or you can grow in insolation, in blocks, as George suggested. If you are growing in blocks and using isolation to keep cross-pollination from occurring, you need a minimum of about 4-5' between different tomato varieties. Some people also plant a barrier plant (something tall and coarse works best) in between different groups of varieties to help reduce the chance of crossing. Sunflowers are especially useful as barrier plants. If you save seed and trade it with other gardeners, it is best if you state your blossoms were bagged so the recipients of the seed will know the seed they receive from you will not be cross-pollinated.

The reason currant tomatoes cross more easily is because they are Lycopersicon pimpinellifolium instead of Lycopersicon escultentum which means they have exerted stigmas (making them "promiscuous", so to speak) so they will cross with every other tomato in your garden.

If you want to save seeds from currant tomatoes, you'd have to bag those blossoms for sure if you are growing more than one currant type, or you could grow them in isolation from all other tomatoes--and the recommended isolation distance is 1/4 mile.

Tomatoes that cross readily, in addition to the currant types, are the potato-leaved varieties and any early fruit on the large-fruited beefsteak types that were formed from double blossoms. Double (or larger) blossoms, referred to as 'megablooms' by some tomato growers form in such a way that their stigmas are exerted, similar to those on the currant tomatoes. Later on in the season, when double blossoms are rare, the larger-fruited beefsteaks are less likely to cross. Modern-day hybrids are less likely to cross than heirlooms because most of them have totally retracted styles.

A surprising number of tomato afficianados do not bag blossoms because time and experience have taught them that they can expect a cross-pollination rate of only about 5%. Some people who don't bag blossoms say their cross-pollination rate is much higher than 5%.

Finally, cross-pollination is not necessarily a bad thing. Many tomatoes grown nowadays developed naturally as a result of cross pollination. A couple that come to mind include "Lucky Cross" and "Little Lucky" (from Craig LeHoullier) and "Earl's Faux" from the garden of Earl Cadenhead.


    Bookmark   March 8, 2009 at 8:17AM
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Okay, so for eating, it doesn't matter where we plant them - the fruit will be true to type regardless of pollination. But for saving seed, it will matter. Thanks all!

And thanks for the Word doc, George! I read it and it's good stuff.

    Bookmark   March 8, 2009 at 12:09PM
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Hi there. Does tulle bagging (or similar methods) actually guarantee prevention of cross pollination - I mean what about wind pollination? I don't know much about pollination but I think pollen is microscopic in scale, so getting through the tulle mesh should be no problem for it.

Does anyone know a method for 100% CP negation for the home gardener (don't have 500+ feet to work with here)?

And any idea about how to stop CP for plants that rely on wind/insect pollination (don't have complete/perfect flowers)?

I heard about taking a paint brush and transferring pollen from one flower of the same species/variety to another.

Any help will be greatly appreciated. Thank you!!

    Bookmark   May 19, 2010 at 1:34AM
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Okiedawn OK Zone 7

Rex, Tulle bags are more commonly used for keeping insects off fruit because tulle is a netting type of material. To exclude pollinator-type insects and pollen with a higher degree of certainty that cross-pollination not occur, you need a solid type of material like organza (I buy little organza bags meant for wedding favors or for rice at weddings, and get them on the wedding/craft aisle at Wal-Mart) or Reemay/Agribon floating row cover type material. You even can use plant cages made from wood-framing covered with a Reemay or window screening type material.

Most vegetables are not wind-pollinated, although corn is and spinach also is primarily wind-pollinated. Most trees and grasses are wind pollinated as are grain crops.

Isolation distances as given in most literature apply more to commercial seed production than to home gardeners. In the case of tomato plants, many long-time seed-savers see very few cases of insect-caused cross pollination even if they do nothing to prevent the cross-pollination. The rate is generally about 2 to 5% although it can vary depending on the tomato varieties involved and whether any of the plants have exerted stigmas.

For other vegetables, it varies quite a lot and it would take a book to explain what is necessary for each and every vegetable crop. Is there a specific one or ones that you're wanting to work with? Even if you manually pollinate using a brush or Qtip or fingertip or whatever, you still have to bag the blossom to prevent other pollen from landing on the flowers.

Large producers of seed, like the Seed Savers Exchange (, use a combination of distance and time isolation as well as caging of plants to prevent cross-pollination. SSE might have some photos on their website that shows some of their caged plants.

I've linked the Cross-Pollination FAQ from the GW Tomato forum below. It goes into quite a lot of detail about tomato pollination.


Here is a link that might be useful: Cross Pollination of Tomatoes

    Bookmark   May 19, 2010 at 12:33PM
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Thanks for the quick reply Dawn!
Besides lima beans, tomatoes, and peppers ~

I have the following non-self pollinating plants that I'm worried about:
-butternut squash cross pollinating with zucchini
-orange/red/white/purple carrots cross pollinating with each other
-melons like watermelons, canary melons (not sure if these can cross pollinate)

I have some really interesting varieties and I'd like to save true seed for next year.
Thanks for the link, but I've already read that entire FAQ before coming here. It was where I got the tulle idea from :).

I'm not too familiar with fabric types. What's organza like? Do you think I can reach a reasonable degree of seed-trueness with some organza bags?

Thanks again for a ll the help.

    Bookmark   May 19, 2010 at 4:58PM
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The carrots will easily cross pollinate. To prevent them from crossing, one would either have to grow only one variety within 1/4 mile, or actually build a little tent around each variety, using very fine netting. Then, you would have to introduce some kind of pollinating insect into the little tent.

No worry about zucchini and Butternut crossing. They are from two different species.

The canary melons will cross with other kinds of melons. But not watermelons, as they are different species. To prevent crossing of melons you could hand pollinate.

Tahlequah, OK

    Bookmark   May 19, 2010 at 5:14PM
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Okiedawn OK Zone 7

Rex, Whereas tulle is like a netting (picture graph paper with tiny squares and the lines are the tulle fabric and the squares are air space), organza is a solid weave. Organza is similar to sheer window curtains that filter light but still allow light to come through, except organza is shinier and fancier than sheer curtains. You see a lot of organza used as the upper layer (with heavier fabric beneath it) of party dress or wedding dress type clothing).

For radishes, they are outbreeding plants that rely on insect pollination. They'll possibly cross with any radish, wild or domesticated, within a half-mile, so you'd have to bag them or cage them and use hand-pollination.

Butternut squashes and zucchini won't cross with each other. Butternut is Cucurbita moschata so it will cross with all other C. moschata types but not with zucchini, which is Cucurbita pepo.

Various carrots would cross with one another and also with the wildflower/weed called Queen Anne's Lace. I'd put them in cages using wood framing and either Agribon or Tull netting to keepout insects. Your carrot flowers cannot touch the netting, screening or other material used to make cages or bees can reach through the cage material (if it is a net or screen type material) and cross-pollinate them. It is hard to save seed. If you want to do it, you need to use the seed to root to seed method that requires 2 years. If you're serious about doing this type of seed-saving, you need to read Suzanne Ashworth's book "Seed to Seed" which goes into great (and wonderful) detail on each veggie.

Watermelons and canary melons will not cross with each other. Watermelon is Citrullus lanatus so will cross only with other melons in the Citrullus lanatus group, like citron melon. All watermelons cross with one another and a half-mile isolation distance is recommended if you don't bag blossoms.

Canary melon is in the Cucumis melo group (along with all other melons that are not watermelons). Cucumis melons all will cross with one another if you don't bag blossoms, but won't cross with any watermelons or any other members of the Cucurbitaceae family. It is hard to hand-pollinate and bag melons for seedsaving because about 80% of the flowers abort and don't set fruit. Once again, 1/2 mile isolation is recommended. One way to do this is to only grow one kind of melon a year and hope no one within 1/2 mile is raising any melons...and hope there's no wild melons around.

Hope this helps. Do you already know what to do with tomatoes, peppers and lima beans?

I'll be back later to see what your answer is. Need to run check on the violent weather.


    Bookmark   May 19, 2010 at 5:33PM
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In response to the first post. I tried logging on at work and never could get logged on. Most of my experience has been with saving tomato seeds and some pepper seeds. So far I've never had any crossing problems with my tomatoes. Knock on wood. I sent out several seeds to people this year and it could be the first. We have very few pollinators around here. I trade a lot of seeds and have bought from SSE members in the past. I would say at least 80% if not more of those who I've either traded with or bought from don't bag blossoms or cage plants. They usually state that up front as I do. When growing large numbers of plants and many different varieties bagging takes a lot of time. And here where we have so much blossom drop in the summer. You have to bag several blossoms to get a few that set fruit. In the future when I start plants in the greenhouse in containers early I might bag a few. Now I try to save seeds from early fruits and also those closer to the middle of the plant especially on my sprawlers. I try to avoid saving seeds from a fruit that is real close to or touching another variety. In a few cases if I've had a large fruit or something I have saved from an exterior fruit and made a note and kept those seeds separate. I'm growing a few Indian Stripe plants from a large fruit that was on the outer edges of the plant last fall. I also try to notice if there is a lot of pollinator activity and avoid saving fruits set during that time. I used Garlic Barrier last summer. This cut down on all insect activity which should of lessened the chance of flying insect cross pollination. I also space all of my sprawlers on 4 ft spacings. I put my first caged plants a little closer this year. Will probably go back to 40 inches on the remainder. From my research and the opinions of other tomato growers I know and also some veggie growers and horticulturalists around here I feel my cross rate should be no more than 2 or 3 percent. I haven't seen any yet but when I do I might see several . Unless you bag or put a cage over a plant there is no 100% method. I'm willing to live with the possible 2-3 % of crosses in order to be able to save seeds. Of all the plants and different varieties I've grown I've had very few crosses show up. Most of them have been with commercial grown seed. Which may of been just mixed up seed instead of a cross. With peppers I know my chances of having a cross is higher. So far I've only grown my saved seeds and haven't shared any. As a smaller grower I feel that I have to take some risks or I would never save seeds. Which I didn't for several years after reading posts from several that said you had to isolate by large distances, bag or cage. I have 2 acres which is more than many. And even with that much room if I tried to isolate by distance I wouldn't be able to grow many different varieties. And as I mentioned above bagging takes time and more record keeping. It is a personal decision on what amount of risk you are willing to take. Here in my garden I feel the risk especially with tomatoes is minimal. If I have a cross I may like it. In closing I will summarize what I hoped to get across. If saving for yourself know the parent well so you can recognize any cross. If sharing just make it known you didn't bag or isolate by a huge distance. But don't let the possibility of crosses keep you from saving seeds. Just my opinion. Jay

    Bookmark   May 19, 2010 at 7:23PM
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Hi everyone. First off I'd like to say thanks for all the replies and help.

I think Zucchini can be crossed with Butternut ~
A lot of you are telling me they can't but isn't it true that 2 species from the same Genera can cross pollinate?
Both zucchini and butternut come from Cucurbita.
I was thinking about it like this:
Zedonks are made from zebras and donkeys, both of which are different species, but both belong to the same Genera Equus.

As for my plans, I think I'll end up going with something along the lines of this:
- Wrap maybe 4 buds for each species I want to save seed for with organza wedding favor bags.
- When they bloom, take bags off and manually hand pollinate them. Replace bags after finished.
- Wait for fruit and remove bags.

Somewhat simple and cost efficient.
I mean if I can get 1 or 2 true seed fruits for each variety I want to save, that should be enough.

    Bookmark   May 21, 2010 at 2:54AM
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Sorry for the double post, but I'd like to clarify that the method I stated above will be used for non-self pollinating plants.

For lima beans, peppers, eggplant, and tomatoes, I'll just bag up a cluster or two of flowers since they wont need manual hand pollination to fruit.

Here is a link that might be useful: [Here is where I found out about which plants self pollinate and which don't]

    Bookmark   May 21, 2010 at 3:00AM
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Okiedawn OK Zone 7


With all due respect, it doesn't matter if you think that zucchini, which is Cucurbita pepo, will cross with Butternut squash, which is Cucurbita moschata, because it will not. I won't even address your zedonk example because that involves animal genetics and we're discussing plant genetics. You can't mix apples with oranges.

You have to understand the Cucurbita genus a little better, which contains 12 or 13 different species or species groups, of which 5 OR 6 are domesticated species grown for food but of those, only 4 species of squash are grown by most people. Here is the key: each Cucurbita squash species (moschata, pepo, argyrosperma, and maxima) crosses with other squash within its species (and each species has dozens of individual varieties) but the species do not cross with one another, with one notable exception that I'll explain in a minute. So, people who save seed can indeed grow one pepo variety, one maxima variety, and then EITHER one moschata variety OR one argyrosperma variety with no fear of them crossing.

With the C. moschata and C. argyrosperma combination, you possibly can have cross pollination, but only if the C. argyrosperma is the female and the C. moschata is the male. You don't get the reciprocal cross. With these crosses, there is little research about how/if they do or do not cross in home gardens because the research has been done with wild squash and Mexican cushaw types, and most people don't grow those types in home gardens.

People who have cross-pollination issues usually have them because they don't understand which varieties belong to which species. Each species has its own specific stem, flower, seed, and leaf characteristics.

Here's a very brief description of what they are.

Cucurbita maximas have very long vines, very huge and hairy leaves, and somewhat soft, round, spongy, hairy stems. They produce seeds that are either white or tan with either cream-colored or tan margins and a thin cellophane type seed coating. The maxima species includes all varieties of Banana, Buttercup, Hubbard,, winter Marrow and Turban types. In her book, SEED TO SEED, which is the definitive book for folks interested in seed-saving, Suzanne Ashworth lists several hundred maxima varieties.

Cucubita argyrosperma (formerly known as C. mixta) have spreading vines and large, hairy leaves. Each fruit's stem is hard, hairy and slightly angular. At the point where the fruit attaches to the stem, the stem flares out only very slightly. The leaves of C. argyrospermas are lighter in color that those of C.moschata, they have rounded leaf tips and few if any indentations along their sides. Their seeds are either tan or white with a very pale martin. The seeds have a thin cellophane coating and cracks in the skin coat on the seeds' flat side. C. argyrosperma includes most but not all varieties of Cushaw squash (excluding golden cushaw, orange cushaw and orange-striped cushaw which are C. moschata), and many other squash including native types like Gila Cliff Dweller, Hopi, Cochita Pueblo, Hopi Taos, and Hopi Teardrop. In her book, Suzanne Ashworth lists several dozen varieties from this group.

C. moschatas have spreading vines and large, hairy leaves. With these, the fruit's stems out very noticeably at the point where it attaches to the fruit. The stem is very hard, somewhat angular and hairy. C. moschata's leaves are a bit darker than those of C. argyrosperma but they have pointed, not rounded, leaf tips and slight indentations along their sides. C. moschata seeds are small and oblong in shape, beige in color and have a darker beige margin. Within this species, you have all varieties of butternut squash, all varieties of of Cheese squash or Cheese pumpkins, and many others. Suzanne Ashworth lists probably a couple hundred from this species in her book.

C. pepo plants have very prickly leaves and very prickly stems, and they are especially prickly by the time they mature. WIth these, the fruits stems are very hard at maturity and have five sharply angular sides. They produce cream-colored seeds that have white margins. This is a huge family that includes all varieties of Acorn squash, all varieties of Cocozelle, some but not all pumpkins, all crookneck squash, all scallop squash, all vegetable marrow squash, all zuchinni squash, and more. Suzanne Ashworth lists many hundreds of varieties that belong to this group and that includes many decorative striped and warted gourds.

All squash varieties are outbreeding and are insect-pollinated plants. There techically are six species: argyrosperma, maxima, moschata and pepo as described above, and also C. ficifolia, a species grown in Mexico and used in candy-making, and C. foetidissima, a wild gourd commonly called Buffalo gourd. The name foetidissima is a clue that their leaves have an unpleasant odor. The fruit are used for oil (from their seed) but are not eaten.

For seed-saving to be done properly to preserve the characteristics of each variety, you need to ensure a greater amount of genetic diversity by choosing your male and female blossoms from different plants of the same variety. If you save from a very small population of plants, over time you will have lower and lower quality of plants and fruit as you lose genetic diversity.

I don't rely on anything I find on random websites on the internet because there is a lot of misinformation out there and often the info given is too general. I rely on books written by acknowledged experts and on info from university or agricultural extension websites.

If you are truly interested in saving seed, you need to buy or borrow a copy of Suzanne Ashworth's book "Seed To Seed: Seed Saving and Growing Techniques for Vegetable Gardeners" which is the definitive book on the subject. If you are interested in the squash family, do yourself a favor and read Amy Goldman's outstanding book "The Compleat Squash: A Passionate Grower's Guide to Pumpkins, Squashes and Gourds".

To save seeds successfully, you have to have a broad-based knowledge of the types of plants you are growing and a thorough knowledge of seed-saving and the techniques needed to do it properly. You need to know not only how to do it but also why it must be done a certain way. Simply hand-pollinating and bagging a few blossoms is a minimalist approach that can give you seeds that run out if you aren't careful. Running out means that you lose genetic diversity with each generation you save because you are saving too few seeds from too small of a population. What you consider simple and efficient leads to weaker and weaker seeds and plants over time and isn't recommended. I'm not saying that to be mean but just to emphasize that there's a better way to do it.


    Bookmark   May 21, 2010 at 6:39AM
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Glenn Drowns has, on ocassion had c. Moschata crosses (if I recall) with banana squash (a c. Maxima). But there were special conditions, which I do not recall. Also, c. Moschata has been crossed to c. pepo, but only under laboratory conditions. Dawn's explaination, above, is correct, for purposes of the home seed saver. Remember, Rex, cucumbers are also cucurbitae, yet by no stretch of the imagination could they be considered squash.


    Bookmark   May 21, 2010 at 8:31AM
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Okiedawn OK Zone 7

Hi George,

I'm glad you saw this. I was counting on you reading it and fixing anything I got wrong or omitted. You're such a squash-growing and seed-saving pro and I am such an amateur.

I deliberate ommitted cukes because Rex didn't mention that he was growing any. I did think about adding them, but then I really would have been writing and writing and writing forever.

Squash just take up so much darn space! I'm only growing 10 or 12 this year, but if they weren't such space hogs, I'd grow more.

I knew you'd said before that Glenn has had crosses, but I couldn't remember if they were deliberate as one of his breeding experiments or accidental. I can never mention Glenn or Sandhill without mentioning that he bred the Blacktail Mountain watermelon, which is and always will be our family's absolute favorite watermelon. I wish he'd write a book. (You're a good friend of his, so maybe you could encourage him to write one when he retires. I know he's too busy now.)


    Bookmark   May 21, 2010 at 8:45AM
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Clip. Clip. Clip. Clip.

"But don't let the possibility of crosses keep you from saving seeds." Thanks for that, Jay. I mean, if I'm using stable varieties what do I care if they cross when I'm in serious need of food? My goal is to keep fresh seeds available. I do have a lot of space, tho.

thanks all!

    Bookmark   June 7, 2014 at 8:25PM
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