Marguerite daisies (Argyranthemum spp.) are often confused with shasta daisies, but have a more rounded, bushy form. They bloom from spring to autumn frost and prefer cool, mild temperatures. In cool climates, the plants die back during the winter and require little pruning to keep their shape. In warm climates, they may become woody or straggly. Annual pruning improves their appearance.
Although deadheading isn't necessary to encourage new blooming, removing spent flowers improves the plant's appearance. Pinch the white, yellow or pink flowers off the stem once they wither and die.
In warm regions, cut back one-third of the plant's growth in the spring to remove woody stems and stimulate new growth. As the plant grows, occasionally pinch tips back 5 to 7.5 cm (2 to 3 inches) to encourage bushy growth. Otherwise, the plants become leggy, with sparse growth at the base of the plant.
Divide marguerite daisies every two to three years, as the plants become thick and wide. Marguerite daisies typically grow 30 to 90 cm (1 to 3 feet) high and spread up to 45 cm (18 inches). To divide the plants, dig them up in early spring. Gently cut the plant in half with a spade or shovel and replant both parts, spacing them at least 45 cm (18 inches) apart. Dividing marguerite daisies not only improves their health, but increases your plantings.
Occasionally, when the base of the plant becomes thin and straggly, marguerite daisy plants may break apart. If this occurs, prune the plant back severely to 10 cm (4 inches) high. Keep the plant well watered to reduce stress. Over a season or two, the base of the plant will grow back and the plant will recover.