Tomatillo Isolation Requirements – Setting the Record Straight

Pollination

One of the most basic concepts of seed saving is that in order to ensure a variety remains true, two varieties of the same species must be isolated from one another. The proper isolation distance depends upon how the crop pollinates.

Cross-pollination occurs when pollen is delivered to a flower from a different plant of the same species. Self-pollination occurs when pollen from a flower pollinates itself or other flowers on the same plant.

Misunderstanding Tomatillos

One crop that is constantly misunderstood among seed savers is tomatillos. Tomatillos are outcrossers, meaning that their flowers cross-pollinate and are incapable of self-pollination. 

One listed member in the 2013 Seed Savers Exchange Yearbook provides this description of ‘Cisineros’ tomatillo, “These were grown next to the 2 other varieties I’m listing—Everona and Giant Yellow. Tomatillos are considered self-pollinating and inbreeding.” 

This is not an isolated case. A quick Google search on seed-saving instructions yields similar misinformation regarding tomatillos. A publication from the University of Georgia, Specific Seed Saving Instructions for Common Vegetables, states, “Tomatillos are self-pollinating and do not commonly cross.” 

Even Suzanne Ashworth’s Seed to Seed considered the authoritative guide to seed saving for many years, states, “All of the species of Physalis are inbreeding plants and have flowers that are perfect and self-pollinating.”

Tomatillos Must Cross-Pollinate

Unfortunately, this misinformation has resulted in many cross-pollinated tomatillo varieties, which we have encountered when we grow tomatillos for evaluation here at Heritage Farm. 

In 2014, Seed Savers Exchange conducted an experiment where we bagged the blossoms of tomatillos to see if they could self-pollinate. We discovered that tomatillos are in fact self-incompatible, meaning that their flowers cannot self-pollinate. In other words, tomatillos must cross-pollinate in order to set fruit, and they rely on insects to do so.

The most recent information on proper tomatillo isolation distances reflects this reality. In Seed Savers Exchange’s 2015 publication, The Seed Garden, the recommendations for distance isolation are 800 feet to half a mile. If genetic preservation of a variety is the goal, “the isolation distance should be increased to 1-2 miles.” This is a significant departure from most seed-saving resources on tomatillos! 

So, if you have a favorite tomatillo variety for turning into salsa verde and want to save seeds, make sure you give it plenty of space from other varieties!

This post was originally published on October 26, 2015.

Seed Savers Exchange is a non-profit organization located in Decorah, Iowa, with a mission to conserve and promote America’s culturally diverse but endangered garden and food crop heritage for future generations by collecting, growing, and sharing heirloom seeds and plants.