Los Realejos claims, with good reason, to have more fiestas per inhabitant than any other municipality in the Canaries. That shapes its agenda: a dense calendar of neighbourhood fiestas, romerías and patron saint celebrations spread across the whole year, plus the usual cultural programming of theatre, concerts and council workshops.
You'll see it all here, ordered by date. Filter by category if you're after something specific; if you want free plans, the price filter will leave you most of the fiesta calendar, which is open to all.
The unmissable one is the Fuegos del Carmen in late May or early June, reckoned to be the biggest fireworks display in the Canaries and one of the biggest in Spain. They're set off from Cruz Santa and visible from half the Orotava valley, so you don't have to be in the municipality itself to enjoy them.