Seed Saving: Determining What Will Cross

Like my other recent seed saving posts this one is mainly targeted at vegetables, but some of the ideas here may be able to be applied to other plants as well. I will also be trying to address the simplest ideas of this subject, and for those who want more detailed information I would refer you to the two books I mentioned in my last post.

Many people who save their own seeds avoid the issue of cross-pollination by only growing inbreeding plants. When growing out-breeding plants, or breeding your own varieties, it’s important to know which plants in your garden will cross with each other.

Unfortunately, this is not an exact science. Sometimes plants that are not supposed to cross do, and others you think should cross don’t. Sometimes vegetables can unexpectedly cross with nearby flowers. Opinions change on this subject, and reference books are rewritten. Often gardeners and/or scientists have conflicting opinions on this subject. There is however a lot known about this subject, and when you are thinking about saving seeds from an out-breeding variety it’s worth researching it and seeing what you can find.

The first thing you should look at when considering the possibility of plants crossing is the Latin names of the plants involved, and the families the plants belong to. I wrote a post about this several months ago. Usually, but not always, plants with different Latin names will not cross with each other. Most plants with the same Latin name will cross with one another.

Besides reference books, and the Latin names, your best bet is to ask other gardeners what their experiences are. In addition, there are a few commonly known guidelines for some vegetables, and I’m going to cover some of them below.

Squashes and Pumpkins

This type of plant has four common different species, and therefore different Latin names: Cucurbita pepo, Cucurbita moschata, Cucurbita maxima and Cucurbita mixta. These don’t usually cross with each other, and by choosing carefully it’s possible to grow four different varieties next to each other without cross-pollination issues.

Many people employ hand pollination techniques to keep different varieties of these plants from crossing, but I’m not going to get into this here.

Melons

Almost all melons are Cucumis melo, and will cross-pollinate with one another.

Beets and Swiss Chard

All beets (garden, sugar and mangel) and Swiss Chard are Beta vulgaris, and will cross with one another. These are also all biennials, and will go to seed in the second garden season. These are out-breeding, and the pollen is carried by the wind.

Beans

Most ‘ordinary’ beans are Phaseolus Vulgaris, and will cross with one another. These are mostly inbreeding plants, but are sometimes cross-pollinated by insects. These beans will not cross with other kinds of beans.

Lima (butter) beans are Phaseolus lunatus, and are somewhat out-breeding plants that will cross with one another. They are usually crossed by insects, so different varieties can be grown next to each other if they are grown under row covers or other means are used to keep pollinating insects off of them.

Soybeans are Glycine max, and are mostly inbreeding so different varieties can usually be grown next to each other.

Carrots

Carrots are Daucus carota, and are very outbreeding plants. The pollen is very fine and carried long distances by the wind, making it very hard to save seeds from more than one variety at a time. To make matters worse, carrots will cross pollinate with Queen Anne’s Lace, a common weed in many areas. In fact if Queen Anne’s Lace is very common in your area, you may simply not be able to save pure enough carrot seeds.

Because Queen Anne’s Lace has a white root, if you are saving seeds from white carrots you may not notice crosses when they do occur.

Because carrots are a strongly out-breeding plant, a minimum of 40-50 plants are generally needed to insure a large enough genepool remains in the saved seeds, but these can generally be planted very close together to conserve space in the garden.

Brassicas

In English, these are often called cole plants, and are the cabbage family.

Cabbage, Broccoli, Brussel Sprouts and Cauliflower are Brassica oleracea, and will easily cross with one another. Most other Brassicas are distinct species and will not cross, but sometimes they do! Turnips and rutabagas are distinct species and will not cross with each other or Brassica oleraceas.

These are very out-breeding plants, and depend on insects for pollination. Because plants are generally not able to self-pollinate, but rather require an insect carry the pollen from one plant to another, isolation is not as simple as covering the plants with row covers. In fact, if you normally cover these plants with row covers in order to keep caterpillars off of them, you will need to remove these to allow cross-pollination of the plants.

Isolation of the plants can be achieved with covers on alternating days, usually this is done with a screen cage that can easily be picked up and moved.

Because these are very out-breeding plants, often a large number of them are needed to maintain adequate genepool size, often requiring a lot of garden space.

Because of all these complexities, Brassicas are often thought of as more advanced plants for seed saving.

Corn

Corn is very out-breeding, and the pollen is carried long distances in the wind. If you live in an area where corn is grown commercially, there may be so much pollen in the air that it’s impossible to properly isolate your plants from cross pollination. This is particularly important of course if you are trying to protect your seeds from contamination from locally grown commercial GM varieties.

Bagging and hand pollination techniques can be used to grow different varieties next to each other, but I’m not going to get into this here.

It’s also possible to choose an early and a late variety, with different pollination periods, and collect seeds from both without cross-pollination problems.

Because corn is very out-breeding, you will need 150+ plants in order to maintain the genepool.