There are several ways to protect tomatoes from cross-pollination. Tomatoes don’t cross-pollinate easily because they usually self-pollinate before the flowers open. However, if a bee arrives loaded with pollen from another variety, a cross or hybrid may occur. You won’t know that the flowers were cross-pollinated until the following year, when you plant the seeds you saved from the resulting fruit.

For home gardeners with limited space and a desire to grow many varieties, there is one really practical method. You have to prevent pollinators from landing on one or more flower clusters that will eventually make fruit for seed saving. The easiest way to do this is to put a thin fabric covering over the flower clusters. This is called “bagging”.

How Do You Do It?

You can make your own bags from purchased fabric like tulle or organza. You can also use floating row cover for bags, but the flower clusters may get too hot in them on warm days, which could inhibit fertilization.

The bags must be put onto a flower truss with unopened buds. You can, however, just take off any open flowers before putting the bag on. Close the bag with the drawstrings, not so tight that the stem will be strangled, but close enough to prevent the entry of insects. Mark the flower stem with bright coloured yarn. If you put the bag onto a flower cluster attached to a terminal bud, you will find that after a week, the bag is packed with leaves. Just take the bag off and reposition it on the flower cluster.

The most important thing to do to make sure that the fruit forms in the bag is to shake it daily. Not just a little tap – you need to simulate the action of a bumblebee. Some varieties form fruit easily in the bag, while others are very stubborn. If you don’t get fruit the first time, put more bags on that variety.

As soon as you see fruit in the bag and all the remaining flowers have withered, take the bag off. Leave the yarn marker in place so you know which fruit to save seed from! Sometimes fruit from bagged flowers are smaller than others on the plant, and they have very few seeds. This indicates incomplete fertilization. The cure for this is to be a better “shaker”!