Seed Saving Isolation Techniques

For the home gardener who is keen on saving his own seed, a common problem can present itself: cross-pollination. Cross-pollination is when a plant is pollinated by another plant, or variety of the same plant, causing the seed produced to not come ‚”true”. Rather, a hybrid of the two parent plants will emerge next season when the saved seed is grown out.

While this can be exciting for the home gardener who loves a surprise, it can also be an annoyance for those who have found their favourite variety and want to be sure that they can grow it year after year.

The good news is, there are some simple techniques that home gardeners can employ to be sure their seeds come true-to-type every year.

Distance Isolation

Distance isolation is using distance between your different plants or varieties, to avoid cross-pollination either by wind, animals, or insects. Distance isolation, while the easiest to use, is also the most difficult for home gardeners who often have plants inter-planted within a small area in order to utilize their gardens effectively. The USDA has a list of recommended distances between plants which can be seen here.

Barrier Isolation

Also known as pollen barriers, this method is often the easiest for home gardeners to work with. It involves creating an actual physical barrier between your plants in the garden to prevent insects and wind from moving pollen from one plant onto another.

There are a few things to take into consideration with this method, such as whether the plant you’re isolating is self-fertilizing (the pollen from one flower falls onto the stamen of the same flower readily, like tomatoes, peppers, and lettuce for example) or will require hand pollination in order to ensure the growth of fruit (squash, melons, and tomatillos, for example, fall into this category).

Organza bags are the easiest and cheapest way to use the barrier isolation method, but it can also be time consuming for those wishing to save a large quantity of seed since individual flowers or flower bunches must be isolated separately. Before a flower is opened, place the bag on the flower. For self-fertilizing plants, wait until the flower dies and fruit starts to form before taking off the bag. For plants that require hand fertilization, remove the bag, pollinate the flower, then replace the bag until the flower dies down. Once the bag is removed, take a piece of coloured string or yarn and tie it around the stem that was isolated, ensuring you won’t forget which to save seed from.

Caging is another method, whereby a cage is created that will fit over the plant completely, usually built out of a wood frame with a fine mesh fabric creating its sides. The benefit of this method over bagging is that the whole plant can be isolated, and thus, every flower that produces fruit is ensured to be pure. However, it is impractical for large plants, like squash, melon, and cucumber vines.

Time Isolation

Time isolation is also another good option for home gardeners, but can be a bit of a logistical problem to figure out. It requires the gardener to plan, either with staggered planting or planting varieties with different maturity rates, so that none that may cross-pollinate are flowering at the same time. It’s an excellent choice for plants that do require insect pollination (like radishes, brassica species, and carrots), but environmental factors can weight heavily throwing the whole system out of whack if the weather is hot, dry, cool, or wet, as these will all effect maturity rates of plants.

Following one of the three above methods, or a combination of the three, will ensure the seeds you’re saving will come true year after year.