Landrace Gardening: Don’t Worry About Plant Purity

Reader Contribution by Joseph Lofthouse
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This week I’m discussing three inter-related topics. Landrace gardeners do not worry much about plant purity because we believe that mixing varieties can promote hybrid vigor and eliminate inbreeding depression. We consider cross pollination to be desirable because it can create more vigorous plants. It may be prudent to grow different populations of the same species as distinct landraces if there are big differences in how they are used.

Heirlooms typically grow poorly in my garden. I believe this is because heirloom seed is often highly inbred. The term “inbreeding depression” describes a general lack of vigor which arises when a cultivar pollinates itself over and over again. Heirlooms typically have little genetic diversity because they have been inbred for up to 50 or 100 generations.

The large seed companies also offer highly inbred seed, but they partially solve the inbreeding depression problem by making hybrids. Then they market the seed as having “hybrid vigor”, which is characterized by the plants growing more robustly than the inbred parents.

The term “open pollinated” is another synonym for highly inbred, because a variety can only “breed true” if it has been significantly inbred. The intense inbreeding makes it possible to offer nearly identical seed year after year.

The plants in a landrace population avoid inbreeding depression because they are genetically diverse and are allowed to cross pollinate. The crossing between different family groups generates naturally occurring hybrid vigor in landraces. The new genetic combinations that arise with each new hybrid allow landrace gardeners to practice survival of the fittest selection. In my sweet corn crop I grow as many as ten thousand new genetically unique plants per year. An industrialized farm might only grow one genotype per year so the crop ends up being essentially a field of clones. So much can go wrong when a farm is only growing one cultivar. So much can go right when a farm is growing thousands of different varieties.

Some crops like tomatoes might only have a natural cross pollination rate of 5%. Other crops like spinach have a 100% cross pollination rate. Either way the principle of survival of the fittest plant selection can be used. I get faster results with higher cross pollination rates. It only takes a few crosses to create huge diversity among the second generation of offspring. At the top of the post I included a photo of the different types of peas that were generated by one manual cross.

There are occasions, even in a landrace garden, where it is desirable to keep varieties separate. I do not like hot peppers to get mixed up with sweet peppers. My sweet peppers can be any shape, or any size, or any color. They cannot be hot peppers! I also don’t like sweet corn and popcorn to cross pollinate, because then the sweet corn gets tough kernels, and the popcorn stops popping.

With other crops I don’t mind at all if they get mixed up with each other. Squash are a perfect example of this. As long as it grows like a squash, and cooks like a squash, and tastes like a squash I don’t care about what color or shape it is.

Here’s an example of a promiscuously pollinated squash. The fruit on the top and bottom are highly inbred. The fruit marked “Banana X Hubbard” is a naturally occurring hybrid. It was particularly tasty: better eating than either parent. I love the huge variety of flavors and textures that can arise in landrace vegetables.

I typically call my landraces “promiscuously pollinated”, because there really is no telling who’s the daddy. I like my landrace crops to be promiscuously pollinated because it leads to increased vigor, and provides more opportunities for survival of the fittest selection. This is part of the reason why I believe that landrace gardening is a path towards food security through common sense and traditional methods.

In next week’s post, I’ll explore using landrace gardening and promiscuous pollination to get what you want from your garden.

Joseph Lofthouse grows vegetables in a cold mountain valley where he practices the art of landrace gardening in order to feed his community more effectively.