Camellias are long-lived trees and shrubs that provide year-round glossy-green foliage and cool-season flowers. Cultivars of Camellia japonica (Japonicas) and Camellia sasanqua (Sasanquas) are the most commonly grown types of camellias. There are hybrids as well (look for an “X” in the plant name), created by crossing cultivars to achieve different colors, shapes, or desirable characteristics such as cold hardiness or unusual growth habits. While they’ll do fine if left alone, camellias will truly thrive when provided with appropriate growing conditions, timed pruning and fertilizing, and good garden hygiene.

Feed with an acid-forming azalea or camellia fertilizer in spring, after the flowers have dropped; fertilize again in the midsummer if growth seems sluggish or foliage looks sparse and begins to lose its deep green color (take care to water the plants the day before feeding in summer). Select a fertilizer specifically blended for camellias or azaleas. Apply at the rate recommended on the label. Don’t overdo it, as plants grown in fertile soil need little fertilizer―and never feed plants that are sick or distressed. Do not fertilize after August, as the plants will be entering a period of dormancy. Fertilizer could cause unwanted growth without enough time to harden off before cold weather.

Main source- https://www.monrovia.com/how-to-grow-camellias/