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How to Prevent Cross-Pollination for Seed Saving

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Close-up of a bee on a yellow tomato flower.

If you are interested in trying to save seeds from your garden to plant again the following year, one of the most important things to figure out is how to prevent cross-pollination to make sure that your plants are still true to type and haven’t crossed with other varieties in your garden.

If you don’t care about trying to preserve the qualities of the plant that you are growing, or if you don’t mind experimenting with growing varieties that have cross-pollinated, then you won’t have to be quite so careful about making sure your seeds have stayed true to type.

But if you are planting Canada crookneck winter squash, for example, and you want to make sure that the seeds you save this year will produce a Canada crookneck squash again next year and not an unknown crossed variety, then you’ll want to take some steps to make sure that your seeds stay true to the variety that you are planting. This is especially important if you are trying to preserve old historic heirloom varieties.

(Important note: If you want to save seeds that are true to the original variety that you planted, you can only save seeds from heirloom open-pollinated plants. If you try to save seeds from a hybrid plant, the plant you grow the following year won’t be the same variety as the one you saved the seeds from. You can read more about basic seed-saving tips here.)

Depending on which plants you are growing and how serious you are about making sure that they don’t cross-pollinate you can try one of more of these tips below. And for the best results and the most success with preventing cross-pollinating you can combine several of these tips together.  

5 Tips to Prevent Cross-Pollination for Seed Saving

1) Be Familiar with Each Variety You Plant

This tip isn’t so much about preventing cross-pollination as it is about being able to recognize whether or not it has happened. The more familiar you are with the variety of the plant that you are trying to save seeds from the easier it will be to tell if your plant has cross-pollinated or if it is still true to type. If you know what the plant and the seeds are supposed to look like, it will be easier for you to spot any variations that might occur. 

I always like to save a few of the original seeds that I bought from a seed company that I know are true to type so that I can use those as a comparison to see what the seeds should look like. If I have some bean seeds that are a cranberry color, for example, I’ll know that they have probably cross-pollinated if I start seeing white spots show up on beans that are supposed to be a solid cranberry color. 

2) Choose Self-Pollinating Varieties

One way to help to prevent cross-pollination is to plant self-pollinating varieties. These varieties are ones that don’t need bees or other insects to pollinate them, so they are a lot less likely to have issues with cross-pollination. A few types of vegetables that are self-pollinating are beans, peas, and tomatoes. 

This isn’t a completely fool-proof strategy, though, and I’ve still had some cross-pollination happen in my garden before, but it’s rare. So if you really want to ensure complete purity of the seeds you are saving then this step might not be enough, but otherwise this can be a good enough way to prevent cross-pollination for these types of vegetables if you are careful to make sure the seeds you save look the way they are supposed to look. If you notice any variation in the shape, size, or color of the plants from the way that the original varieties look then it would be best not to save seeds from those plants if you are trying to preserve the original varieties.

3) Plant Only One Variety Per Family

This is really the most fool-proof way to make sure that your plants haven’t cross-pollinated. If you only plant one variety of squash, for example, then you don’t have to worry about whether or not that variety might have cross-pollinated with another variety of squash. 

(As a side note, though, squash is actually a bit more complicated because there are different families of squash plants within the overall category. If you look at your seed packet you might see the word “maxima” or “moschato” or “pepo.” So if you plant one variety from the maxima group and another from the moschato group then you won’t have to worry about cross-pollination the way you would if you planted two varieties that were both from the maxima group.)

The two limitations to this method, though, are the fact that this means that you can’t grow as many different varieties in your garden and the fact that you can’t control what your neighbors might be growing. Even if you only grow one variety of squash, your next-door neighbor might be growing a different variety and pollinators could easily go back and forth between your yards. 

4) Isolate Plant Varieties by Distance

Another option if you have a really big property is to isolate different varieties by distance. This isn’t really practical if you have a small yard and a small garden, but if you have enough space then you can spread your different varieties as far apart as possible. Self-pollinating plants like beans wouldn’t need as much space between them, but others would need more space.

It’s hard to give an exact number for how far apart to try to space plants because there are a lot of variables with the type of plant and with the different types of pollinators, but generally the further apart you are able to plant them the better. Seed Savers Exchange has a really helpful plant isolation chart with all different varieties of plants and the recommended distances for isolation along with other good information.

5) Cover Plants and Hand Pollinate Them

Another possible option is to cover your plants with some type of cheesecloth or similar lightweight see-through material that will allow light in but keep pollinators out. This would only be necessary during the time that they are actually flowering, and it would also require you to hand-pollinate your plants by taking something like a small paintbrush and collecting pollen from a male flower and transferring it to a female flower. Here’s some more information about hand-pollinating vegetables if you’ve never tried that before.

If you’re interested in learning more about preventing cross-pollination and seed saving, the SeedSavers exchange website has some really good articles about the seed saving process that might be helpful.

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The information in this post is not to be taken as medical advice and is not intended to diagnose or treat any disease.

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