50+ Seeds. The Serrano hot pepper variety originated in the mountains of Mexico and has been used in Mexican cuisine for centuries. The plants range in height from about 18" to 4'. Serrano peppers turn from green to red as they ripen, although many people prefer them in the green stage. The "heat" varies from 10,000 to 30,000 Scoville units. Generally hotter than a Jalapeno, they can be used in salsa and pico de gallo. Germination can take 3 weeks. Open-Pollinated, 77 days from transplant.