You can harvest your peppers at any point, really; it depends on your needs and wants.

You can manage the heat some on your chile peppers. The general rule is: when the peppers are ripe, they are hottest. Most people are used to green jalapenos and don’t even realize they are usually red when ripe! (Although there are a few purple and yellow jalapeno varieties.)

Also, the warmer the weather, the hotter the peppers seem to get. And remember — chile peppers like hot weather!

If you’re letting the jalapenos get ripe (probably red in your case) and the weather has been hot, then it could be the variety of jalapeno. There are some jalapenos bred to be extra-hot, and some that are bred to be mild.

One more thing; for jalapenos to have much heat, you’ll usually need to keep the seeds and the membranes with the pepper. The seeds and the whitish membrane hold most of the jalapeno’s heat.

Hope this helps!