It used to be accepted practice to cut down most perennials in autumn. Fortunately, as our appreciation for the winter forms and our awareness of the habits of birds and butterflies advances, we no longer mindlessly go out and cut everything back at once, leaving the garden naked of any sign of dormant plants.
Generally speaking, plants that are not pruned in the autumn need to be cut back, or possibly deadleafed, in the spring. Perennials like species of Asarum, Bergenia, Helleborus, and Heuchera need to have their dead leaves removed, particularly if they have been exposed to windburn or sunscald. Epimedium and helleborus need to be cut back early in spring so that the new flowers and leaves are not masked by the previous season’s tattered remains. Rotary mowers can be used on large plantings of epimedium. The groundcover Liriope spicata also can be mown down in the spring. Moss phlox (Phlox subulata) may incur dead branches over the winter, or portions of the plant may die out, and these should be removed at this time. Evergreens may not need any additional pruning in the spring in some years, as their foliage can stay fresh over the winter. Phlox stolonifera and Dianthus gratianopolitanus are a couple that usually fair well. Most often, evergreen basal foliage doesn’t need any additional pruning in the spring.
Certain subshrubs have their overwintering buds aboveground, which classifies them botanically as woody plants, but horticulturally they are classified with herbaceous perennials. They benefit from snow cover for protection and may experience tip dieback on the part of the plant above the snow line. Spring is the time to prune off those dead tips. This group includes evergreen candytuft (Iberis sempervirens), lavender, germander, and thyme. They may also need a hard cutting back in the spring if they start to grow leggy. Lavender normally only needs its dead tips cut off in late spring or early summer, once all the woody growth has had a chance to break. Often the beginning gardener will prune back lavender hard before winter, only to be disappointed that it doesn’t return at all the following spring. Lavender may need a hard cutting back (down to 4–6 in.) in spring every 2–3 years to hold a decent habit if it has become open and leggy, or if it’s being used as a hedge. It can be cut back hard annually for hedging. Perovskia can be cut to the ground to encourage sturdier plants; I prefer to cut mine down to live buds, which can be 6 in. or more above ground.
Electric hedge shears work best for ornamental grasses on large jobs. First tie the grasses together, which keeps excessive debris to a minimum, and then cut it down. It helps to have two people working together on this. Handheld hedge shears do the trick on small quantities. A weed whacker with a rigid plastic blade can also be used. I’ve even heard of people using chain saws, but I’ve never needed such heavy machinery, even for very large grasses. Do wear gloves, as the grass blades can cut like razors. Festuca glauca ‘Elijah Blue’ normally only needs dead blades pulled from within the clump by hand. After severe winters I have had to cut ‘Elijah Blue’ fescue back because of excessive tip burn on the blades.
I do most spring pruning early on, before new growth begins, usually sometime in late March or early April. Gardeners in milder climates may need to get an earlier start. You don’t want a lot of new growth in the way while you are trying to clean up the old stems and leaves. If some new growth is hit during spring cleanup, no harm done—perennials are very forgiving and will be quick to fill in, but if you cut too late you may be altering the plant’s ultimate height, and even flowering time on early-blooming species.
Tracy DiSabato-Aust has earned international acclaim as one of America’s most entertaining and knowledgeable garden writers and professional speakers. She has extensive experience in the United States and abroad with more than 35 years in the industry and is a gifted and award-winning designer who combines artistic vision with practical horticultural strategies.
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