If you are growing only two or three plants each of two varieties, you may be able to get by with a smaller distance, say 50 feet plus barrier plants. Hot peppers as a rule of thumb may require approximately four times as much isolation distance as do sweet bell peppers. Flowers of hot peppers have style and stigma (female reproductive structures) which protrude further beyond the anther cone (male reproductive structure). This situation is called stigma exsertion, and whenever the stigma is exserted, the flower is more likely to be cross-pollinated.
The Lend-Lease Act of World War II states that for peppers, 1/4 mile isolation distance is desirable between two varieties, but the distance should not be less than 150 feet plus a barrier crop between two varieties (1,3). Evidently the 150-foot distance plus barrier crops represents a compromise between purity and practicality. In the absence of hard evidence on NCP as a function of isolation distance (but using the information from the Lend-Lease Act), I am proposing the following guidelines for SSE members which should give 98% or better purity for small plantings. Here the intended use is for preservation efforts where fairly high purity is desirable, where the seed may not be grown out each year and where dissemination is limited. On this basis the following isolation distances are recommended for the SSE:
* Between sweet bell varieties 150' plus barrier crop*
* Between hot and sweet varieties (or between two hot varieties) 600' plus barrier crop
*Note: Additional distance is desirable between long-fruited sweet varieties and sweet bell varieties, or between two long-fruited sweet varieties.
If necessary, modifications of these distances can be made by consideration of factors presented in the preceding Table of Variables Affecting NCP. If you cannot achieve the recommended minimum isolation distances of 150 feet and 600 feet for sweet and hot peppers, there are other alternatives for keeping the varieties pure: