Temporal Isolation

To avoid cross-pollination, two or more varieties of the same species can be isolated by time, where one variety is planted earlier than the other. The first variety must be planted early enough so it can be pollinated and set seed before the second variety begins to flower. This staggered planting technique requires careful observation as well as an adequate knowledge of the plants’ lifecycle and local environmental conditions. This is especially true when more than two different varieties are planted. Some examples of annuals that can easily be temporally isolated are corn, lettuce, basil, and sunflower.

Temporal isolation usually works best using two varieties that have different maturation dates. In some cases, this method can still be used if the said varieties have equal or similar maturation dates, provided the season is long enough for them to be sown at least four weeks apart. Weather variability is another factor to take into consideration, as the variety planted the earliest might not grow as fast as expected at the beginning of the season (due to cool temperatures), and might end up overlapping the second variety planted later (which will have grown faster due to warm temperatures) during the flowering stage. In the event such a situation arises, neither variety should be saved for seeds, as cross-pollination might have already occurred, thus compromising seed purity. If you believe that the flowering period of both varieties will overlap, preventive actions can be taken to avoid crossing by manually removing the flower buds of the earlier variety upon emergence.