Shasta daisies (Leucanthemum X superbum) are undemanding plants, but pruning encourages more flowers and stronger growth. These perennials grow in U.S. Department of Agriculture plant hardiness zones 5 through 9, and thrive in full sun and well-drained, alkaline soils. They benefit from pruning from mid-summer onward, and dividing plants also encourages healthy growth. Shasta daisies grow 2 to 3 feet tall and 1 1/2 to 2 feet wide, depending on the cultivar.
Pruning Shasta daisy blooms as they fade encourages more flowers. Shasta daisies can flower less after they set seed, but removing the flowers before seeds develop prompts the plants to bloom again. Sterilize your pruning shear blades by wiping them with rubbing alcohol, and prune Shasta daisies when their petals droop and turn brown. Hold the flower in one hand and feel down to the base of the flower stem with the other hand. Prune the stem at the base, and remove the other fading blooms in the same way. Sterilize your pruning shears again after use.
Shasta daises benefit from pruning when the earliest blooms start to fade. Check your Shasta daisies every week, and prune fading flowers until late summer or the end of blooming. If the soil surface is dry after pruning, water plants until the water begins to puddle on the ground, and feed them with a liquid 15-30-15 fertilizer, which encourages more blooms. Dilute the product at a rate of 1 tablespoon per 1 gallon of water and apply it every 14 days, or dilute and apply the product according to the instructions on the label.
Severely pruning Shasta daisy clumps in early fall can prolong their lives. Shasta daisies are short-lived perennials, but removing their leaves and stems when flowering is over encourages strong growth, which helps plants store energy for winter. Prune Shasta daisies to 8 inches tall, using sterilized pruning shears, and put the trimmings on the compost pile or in the trash. If your plants are too tall and lanky, pinch out the tips of non-flowering stems with your thumb and forefinger in spring to encourage them to grow more compact and bushy.
Lifting and Dividing
Lift and divide Shasta daisies every two or three years to encourage strong, healthy growth and flowering. Dig up a Shasta daisy plant on a cool, cloudy day in winter or early spring by pushing a garden fork into the soil about 6 inches from the plant base and gently levering it up. Do this three or four times around the base until the root ball lifts out of the soil. Divide the plant into three sections by pushing a sharp spade down through the roots, and plant the sections 24 to 36 inches apart at their original growing depths. Water the plants thoroughly and continue to water them regularly so that the soil stays moist.