When planning our garden for seed growing, there are a number of factors we take into account before we plant in order to insure isolation and thus purity of a strain. One factor that complicates slightly how to isolate in an organic garden is rotations. It’s important to rotate crops so as not to perpetuate diseases, or deplete the soil. When we include isolation factors in a garden growing about 200 varieties, rotation from year to year can be complicated. Without going into great detail of rotations, I just wanted to note that this is another element we consider.
Another factor we consider when planning our isolation needs is the Latin names of the plants. It’s important to know what can cross with each other in order to keep them separate. Some things may seem intuitive, while others are not obvious at all. Many people would probably not realize that collards (Brassica oleracea) and cauliflower (Brassica oleracea) are the same species and would cross with each other. On the other hand, it might seem logical that all squashes would cross with each other, but only those in the same species actually cross. For example, butternut squash (Cucurbita moschata) will not cross with acorn squash (Cucurbita pepo).
Another consideration is how a plant is pollinated. Plants are basically pollinated in one of three different ways. They can be pollinated by wind, insects (or other third parties), or self-pollinated. Seed to Seed, written by Suzanne Ashworth and published by Seed Savers Exchange is one of the best resources we have and use regularly to learn Latin names and how a plant is pollinated as well as many other seed saving questions.
In a small garden, the easiest way to insure purity is just to grow not more than one variety of a species at a time. If you grow only one radish, one carrot, one tomato, chances are you won’t need to worry about isolation. However, in a larger garden like ours, where we’re growing seed for production and preservation, and we’re trying to preserve as many varieties as possible, we often want to grow more than one of a species at a time.
The easiest plants for us to isolate are self-pollinated plants, such as tomatoes. Even though they are self-pollinated, insects could cross them, so we plant them with some distance between and with other plants in between varieties, or in different plots. The distance can be minimal, about 10 feet. But this helps keep the insects from mixing the pollen, and it also helps when we harvest the fruits to not confuse varieties when they are growing and tumbling all over each other.
With insect-pollinated plants, such as squash or cucumber, we use a similar method of providing distance between the varieties to insure isolation, but generally a greater distance is required between plants that are pollinated by insects than between plants that are self-pollinated.
With both insect-pollinated and self-pollinated plants, physical barriers (tall sunflowers), hedgerows (such as clary sage) and lots or nectar-bearing plants are important parts of maintaining isolation. We have many of these things around the farm. These help keep the insects in a particular corner or area of the farm. If there’s plenty of nectar to choose from, and there’s a huge row of sunflowers that they must fly over or around, the insects are more likely to stay in the place they are in, enjoying lunch from the bounty they have, rather than making a huge effort to fly (and cross-pollinate) somewhere else. We use these techniques regularly and have found them to be successful.
With wind-pollinated plants, such as corn, distance is the main and most reliable method we have used to isolate. Most wind-pollinated plants need greater distances for isolation than insect-pollinated. for example corn or beets need two or more miles. Generally, we only grow one variety at a time. We have at times used time to isolate these types of plants. Essentially, we choose two varieties, an early and a late, and we plant the early one first. After waiting a while, we plant the other one. This way the plants are not in flower at the same time. It’s important when isolating this way to pay close attention to the plants and be scrupulous about not letting them flower together. If for some reason they look like there will be some overlap of flowering, then we remove the blooms from the earlier plants, to prevent crossing.
There are ways to isolate corn with bags, but it’s fairly labor intensive and it’s not really practical for our farm and the staff we have available, especially with the quantities that we must grow. If there were only a few plants, and the last remaining seeds of that plant, we would consider isolating in more labor intensive ways.
We have done some limited physical barrier isolation at the farm, although, as I’ve stated, most of what we’ve done has been using time, distance and natural barriers such as hedgerows. We grew Bulls Blood beet last year and we used reemay bags to bundle a number of stalks together to pollinate each other (they are wind-pollinated), and to prevent them from becoming accidentally crossed with any possible Swiss chard in the neighborhood going to seed. They were pollinated and set seed fine.
We also made an experimental attempt at a small isolation cage for Black Round Spanish radishes. We used PVC pipe to make arches over the radishes, then enclosed it all with reemay. This had limited success because we didn’t introduce any pollinators and not very much seed set.
We are interested in expanding our use of isolation cages due to problems like not being able to grow brassicas because of so much wild mustard at the farm. But we are not sure about introducing pollinators versus hand-pollinating, how big or how small to make the cages, and feel we need to learn more and experiment with more common varieties before we rely on cages for a very rare variety. We know that seed saving is a long process and that it can take seasons to learn what we are doing wrong or right, and that it’s important to constantly be checking and affirming what we’re doing. It’s also important to learn from what others have discovered. If you have any pertinent or insightful information about seed saving or isolating, we would be pleased if you shared it.