Native to tropical regions of Central and South America, pepper plants -- including the jalapeno -- have been cultivated for thousands of years. Christopher Columbus transported peppers back to Europe after his invasion of the New World. The spiciness of jalapenos increase with maturity and a jalapeno that is turning black on the plant is no cause for concern.
Jalapenos turning black on the plant are a natural part of the growth and ripening process of the pepper. In fact, this is a signal that it may be time to harvest the jalapeno. The pepper should be picked when it has taken on a blackish-green color. It requires approximately 72 days to reach maturity. Peppers may be broken off easily by hand although some gardeners cut them away to minimize potential damage to the plant.
A jalapeno that has reached maturity will show small cracks around its shoulders at the top of the fruit. They can be picked at nearly any time and are edible and full of flavor at all stages of growth. Still, those who consider themselves connoisseurs of jalapenos will notice a difference when comparing the taste of mature and immature jalapenos. A number of jalapeno varieties exist, all with varying degrees of strength.
The fact that peppers are turning black on a plant does not mean that they absolutely must be picked at that time. There is no set time or absolute indication for harvest; gardeners can feel free to pick the pepper based on taste. Jalapenos typically grow to between 2 1/2 and 3 1/2 inches in length. Endowed with thick walls that hold the pungent taste of the pepper, jalapenos become hotter the longer they grow.
Texas A&M University estimates that 200,000 pounds of jalapeno seed is planted in Mexico each year. The jalapeno is ideal for pickling, canning or as an ingredient in Mexican dishes. The heat can be minimized by reducing the number of jalapeno seeds that are introduced into a dish. Cooks who prefer a milder taste should avoid seeds and utilize only the fleshy walls of the pepper. The heat in a pepper is caused by an oil called capsaicin.