Preventing Cross-Pollination

I would like to start saving my own seed and breeding hardy variates specific to the land I currently "farm." There is of course a concern about possible cross-pollination. Sepp Holzer states in his book that this can be prevented or minimized by planting hedges and/or using raised beds (hugelculture) to separate wind pollinated species. My thinking was that if you set up paddocks each paddock would have a different variety of the same species. For example one paddock may have ali baba watermelons, mortgage lifter tomatoes, and russian red leaf kale -- whereas another paddock would contain orangeglo watermelon, omar's lebanese tomatoes, and lancinato kale. The paddocks would be divided by thick hedges which could also serve to keep animals in or out. Would this work? Also will similar variates of clover cross-pollinate, for example landino clover and strawberry clovers or perhaps sweet clover and subterranean clover? How can I know which variates can breed and which are fine to place together and still be able to preserve true breeding seed? I love the idea of picking the best fruit grown in the worse conditions to preserve and enhance plant hardiness and productivity.

There are three books I can recommend:
- Breed your own vegetable varieties
- seed savers handbook
- seed to seed
There are plants which need a lot of distance like corn for example. I find the whole topic difficult, because I want to grow several varieties and I cannot imagine building cages and that stuff. But I plan to harvest my own seeds because of the apalling quality of commercial seeds here.

James, lots of the vegetables/fruits that you mention are not wind pollinated. They are insect pollinated and hedges tend not to deter insects from visiting lots of tasty different crops. Crops like squashes can have the flowers taped up before they open, then hand pollinated then taped up again and marked. Paula has given some great suggestions for books and I concur that they should give you almost all of the info you need. Yes corn is difficult because it is wind pollinated and sometimes the wind can be strong and blow pollen in from a neighbour's crop - I think the separation distance goes nearer to miles than metres/yards!

thanks for the replies I will take a look at the books mentioned. Do you guys/gals think that paddock separated by dense hedges and forest would prevent cross pollination. My thinking is that if bees or other pollinators have everything they need in a paddock flower wise they will be less likely to venture through a forest or a relatively great distance to get what they can easily get near their home. I like the idea of hand pollinating and then tying the flower closed and this may be needed for select varieties but ultimately I would really like it if each paddock could have a different variety grown in poly-culture. Time to experiment I guess.

Another good method is to stagger your plantings so they do not all blossom at the same time.

It is not only about cross polination. Some plants need a sufficient diverse genpool. Fro example corn or cabbages. That means that you must save seeds from enough plants, which is difficult with cabbages or do you want to eat 200 cabbages?
I try to save what is easy at the moment and buy the rest.

The property I am currently working with is about 40 acres, it is pretty densely forested except in the garden area and areas for buildings. There is one large pasture like area next to the pond-to-be (hole in the ground that doesn't hold water), my thinking was to develop this area and then a few others creating island like paddocks floating in a sea of wild forest. My hope is it be able to breed specific variates in each paddock and because each paddock is so diverse and plentiful pollinators would be less likely to wander from home and if the did they would do so in so few numbers as to not adversely effect my breeding program.
I have been saving seeds from my sunflowers for the a last 3 years, but they haven't been breed for a single location because each year since I started saving them I have moved. I will also try to do this with my cover crop seed this year.

What other seeds have you guys saved, and did they breed true?

This is a very interesting thread. Thanks!

If I understand correctly, it seems that maintaining heirloom strains is a pretty specialized endeavor that might entail sacrifices in terms of amount of food produced.  Is that fair?

If so, this seems to have implications for the range of vegetable choice that would be available if food, transportation and shipping became much more expensive.  

Does the difficulty of maintaining several varieties of the same species, esp. in the case of Cucurbita pepo (squash etc.) and Brassica oleracea (cabbages etc.), mean that if the future becomes so local that buying true seeds every year became prohibitively expensive for most, that we probably wouldn't be able to grow as many varieties as now?

Hugh

Hugh Kay wrote:This is a very interesting thread. Thanks!

Does the difficulty of maintaining several varieties of the same species, esp. in the case of Cucurbita pepo (squash etc.) and Brassica oleracea (cabbages etc.), mean that if the future becomes so local that buying true seeds every year became prohibitively expensive for most, that we probably wouldn't be able to grow as many varieties as now?

Hugh

Not necessarily for a variety of reasons.

One of the first ones is that if shipping became so expensive it would drive food cost up and so make it more economically feasible for local farmers to grow many vegetables that are currently shipped from different locations. We'd also have more people growing their own food. Between both kinds of more producers local seed sources would probably collaborate to produce enough seed to meet demand in the area. Additionally, seed would be a lot less expensive to ship than vegetables so it may remain feasible that there would be national seed suppliers.

Another solution is the fact that most seeds actually have a viable lifespan of more than one growing season. Many vegetables are harvested before they actually produce seed (such as cabbage) and so you have to purposely cultivate them for seed. You can save seed from different varieties on different years and if you store your seed properly you will be able to produce several years worth at a time. How many varieties you can maintain in this fashion is limited by how well you can preserve the seed. Think about those professional seed banks that maintain huge freezer vaults of seeds that are expected to last decades.

Then there's the idea of landrace gardening. If you're interested in knowing more in depth information about it I'd recommend you follow the posts by Joseph Lofthouse. He's a contributor on this site and here's a link to his articles for Mother Earth News http://www.motherearthnews.com/search?tags=+Joseph+Lofthouse The basic concept boils down to rather than worrying about maintaining a pure variety line, you allow the different varieties to blend and then reselect, from the plants that thrive in your conditions, the plants that also have the traits important to you. Such diverse selections actually come out with much more total variety than maintaining distinct lines would produce.

I like the idea of land races best of all. Even saving seed from the survivors in a garden will over time result in the plants adapting to those growing conditions. Adding in more genetic diversity and then using some reasonable thought when you save seed makes this happen much faster. Plus, when your select process is based on what is important to you, you end up with plants that are tailored to your individual tastes.

James: Congratulations on your interest in growing your own vegetable seeds. I highly recommend the practice!

Pollenation is generally a highly localized event with an occasional pollenation from far away. That occasional pollenation from far away can create a huge problem for mega seed companies who are growing enough seed for an entire nation. An occasional cross isn't as dramatic to a backyard farmer. As an example, some years ago, the farm that was growing Delicata squash seed for the world got contaminated by a poison producing gene. They then sent seed for poisonous squash out into the world. I think that the reputation of Delicata squash still hasn't recovered. They were not tasting each squash fruit before saving seed from it, so they didn't have a clue that they were distributing poisonous squash to the world. I had something similar happen in my garden. I inadvertently grew a poisonous melon in with my muskmelons. Because I am a small scale grower, I taste every melon before saving seeds from it. When I found out that I had a poisonous melon growing in my garden, I threw away a whole year's worth of seed production rather than risk distributing poisonous melons. So the mega-seed companies have to be extremely conservative about variety purity. I don't have to be, because my quality control checks are different.

The mathematical probability of cross pollination looks like this. Extremely likely to be pollinated by nearby plants. Extremely unlikely to be pollinated by plants from further away.


In my garden at a separation distance of 100 feet, I get about a 5% cross pollination rate on small plantings of squash. I get about a 5% or less cross pollination rate on corn varieties grown 3 to 11 feet from each other.

Here's an estimation of cross pollination between two 100 square foot patches of carrots growing ten feet apart from each other. Along the edges of the patch next to each other, there is about a 1% chance of cross pollination. That's too much for a mega seed company, but it's just fine on my farm.


Those sorts of low cross pollination rates are something that I can easily live with. Some  cross pollenations are more difficult to deal with. For example, I really don't like surprize hot peppers in my sweet peppers, so I'm very careful about not growing sweet peppers and hot peppers in the same field. But I don't care much if the shape or color of a winter squash varies a bit, as long as it tastes good.

Preventing cross pollination is difficult. Minimizing cross pollination is easy. It's difficult to keep something 99.9999% pure. It's easy to keep something 95% pure. In my garden 95% purity is good enough for most crops. If I don't like a naturally occurring cross, I cull the crosses when they show up. I'm much too lazy to be hand pollinating crops when wind or animals will do it for me.  

Hedges help reduce pollen flow. Distance helps. Staggered flowering times help. The more diversity surrounding a paddock, the more pollinators there will be, and the more likely they will be to produce cross pollination. For example, at my place in the desert, the cross pollination rate on common beans is around 1:200. A collaborator's garden next to a swamp has a cross pollenation rate closer to 1:20. (That's for beans grown side by side, not in separate paddocks.)

Even stored at room temperature, I'm still getting close to 100% germination on many species of seed that I grew 5 years ago.  In one growing season I grew enough Bok choi seed to plant 24 acres. That's enough to provide my community with seed for decades.

I grow seeds for every crop on my farm. A few years ago I counted 70 varieties in 55 different species. I've added many dozens of species since then, and a number of varieties.

I don't try to maintain heirlooms. I plant plenty of heirloom varieties, but I don't try to keep them pure. I let them get open pollinated by other varieties (to the extent that they will). The genes are still hanging around, just not a particular arrangement of the genes. My experience is that cross-pollenation gives me more opportunities to select for varieties that thrive on my farm.

I have 7 isolated fields, so in theory, I could grow seed for 7 varieties of brassicas, and pepo squash per year. If seed is good for 10 years when stored at room temperature, then I could maintain 70 varieties of each species.

I allow impurity in my squash: Taste has to be magnificent.

Thanks, Cassie and Joseph.  This is super helpful!

I am working in a 1200 sq. meter (0.3 acre) space that we are converting to a school garden  on a SE-facing hillside in Switzerland that so far has little in the way of hedges or other vertical separation, so it sounds like the best route is to not worry about cross-pollination in most cases, and save seeds from fruits & veggies that develop well here, but only after tasting them.  

I hadn't thought of actually tasting things before saving their seeds even though this is pretty obvious in hindsight.

I don't care for the taste of raw tomatoes. So I hadn't been tasting them. I felt really chagrined the first time that I tasted fruit from every plant before saving seeds. Tomatoes are mostly inbreeding, so it only took one growing season to fix the problem.

Joseph's seeds GROW. I am putting in roughly half an acre of truck garden this year and am proudly growing some of his varieties to educate the locals on what good food should taste like. With stuff that is at least partly adapted to a not dissimilar climate so it grows well.

I will modify the open pollen drift. Here we have average sustained winds of 25mph and some days (usually around when the peach trees bloom) the days tend to be 40mph. I can only HOPE that some of the pollen zips past and does the job or the pollenating insects can manage against that. In my garden WITH windbreaks, I'd agree on the distances and amount of cross pollination drift. When I truly want to control genetics on seed plants, I will do hand bagging and hand pollination so I know what pollen went where and stays there.

Joseph Lofthouse wrote:
The mathematical probability of cross pollination looks like this. Extremely likely to be pollinated by nearby plants. Extremely unlikely to be pollinated by plants from further away.

In my garden at a separation distance of 100 feet, I get about a 5% cross pollination rate on small plantings of squash. I get about a 5% or less cross pollination rate on corn varieties grown 3 to 11 feet from each other.

Hedges help reduce pollen flow. Distance helps. Staggered flowering times help. The more diversity surrounding a paddock, the more pollinators there will be, and the more likely they will be to produce cross pollination. For example, at my place in the desert, the cross pollination rate on common beans is around 1:200. A collaborator's garden next to a swamp has a cross pollenation rate closer to 1:20. (That's for beans grown side by side, not in separate paddocks.)

I allow impurity in my squash: Taste has to be magnificent.

This kind of information should be useful if I try to save seed from open pollinated squash. I currently have a neighbor living a few blocks down that has a volunteer spaghetti squash growing in her hard. She agreed to allow me to have one of the fruits from the plant once it has matured; however, I was unable to successfully hand pollinate a squash flower from the plant. By the time I got around to hand pollinating the flowers, the plant was already directing its energy towards the production of two already large fruits, so the plant aborted the three female flowers I hand pollinated. I am concerned about the fruit being cross-pollinated with one of my bitter ornamental gourds I grew this year. Although two of the three ornamental gours I harvested fruit from this year were non-bitter, one of the plants had bitter fruit, So I am concerned about what chance there is of the volunteer plant yielding bitter fruit. The neighbor's plant is about 370 feet from my squash plant in my garden with bitter fruit. I have seen recomended isolation distances as large as 1/3 of a mile and as short as 500 feet for squash. If you have observed a 95% rate of seed purity in your squash that you plant at 100 feet apart, what would be the risk of cross-pollination for squash planted 370 feet apart? I live in a suburban neighborhood east of Dayton, Ohio, so there are already a few dozen neighbors who garden living nearby. The only other gardener I am aware of who grew squash this year lives 800 feet away and he was also growing spaghetti squash. In this case, I am more concerned about the seed from my neighbor's volunteer squash plant yielding plants with bitter fruit next year than about the purity of the variety saved from seed.

Ryan M Miller wrote:what would be the risk of cross-pollination for squash planted 370 feet apart?

In the ballpark of 4 seeds per 1000.

I have harvested typically 150-400 seeds per squash, so this means there may be a very small chance that the volunteer spaghetti squash may have crossed with my bitter ornamental gourd (Cucurbita pepo). If one of the spaghetti squash on the volunteer plant were pollinated from more than one plant, then the fruit might have at most one seed that yields a bitter-fruiting plant.

I don't know what effect the type of pollinator would have on the cross-pollination of squash though. From my morning observations looking at the squash plants in my garden, the primary pollinators for squash in the early morning where I live appear to be squash bees (Peponapis pruinosa) and bumblebees (Bombus sp.). I have also seen honeybees (Apis mellifera) on squash flowers, but they tend to appear later in the morning.

I took some pictures of the spaghetti squash fruits. The plant has powdery mildew right now so I give it at most two weeks before the plant is dead.