Spring Cleaning
Cleanup should begin late March/early April.
Pruning:
Evergreen plants not pruned in the fall, such as heuchera, tiarella, epimediums, helleborus, and Christmas fern (polystichum) benefit from a late March grooming. Cut away winter damage on the fern, heuchera, asarum, and bergenia. Fully cut back helleborus, liriope and epimediums. Cut away dead patches on phlox subulata and dianthus. Prune off the dead tips of candytuft (iberis) and lavender teucrium and thyme. With lavender, unless a compact plant is desired, it is often better to prune in late April/early May to determine what is alive or dead. Lavender sometimes benefits from a hard pruning every two to three years.
Do not over-prune artemesia ‘Powis Castle.’ It may die if old wood is cut too much. As for buddleia and perovskia, wait until you see what has survived winter before pruning. Then prune away old wood. You can cut perovskia down each year to a few inches to get a short bushy plant.
Grasses:
In early April, before you start seeing new growth, cut grasses down to about six inches above the ground. It helps to tie the tops first. Electric hedge sheers make the job quick and easy. Cut sweet flag (acorus) and sedges (carex) three to four inches above the ground. Do not cut fescue or blue oat grass (helictotrichon), just pull away dead blades. April is a great time for dividing grasses. Dainty tools do not help with this job.
General Cleanup:
Late March or early April, rake away dead leaves and debris. Doing it in stages helps the plants adjust. Cut down the plants left up in the fall, like the fronds of ferns. Push the roots that have been heaved up by frost back into the soil. Apply lime to the perennials and vines that like a sweet soil. Clematis, bellflower, delphinium, dianthus, lavender, iris, candytuft, hollyhocks and peonies all fall in this category. In April, apply Plantone, an all-purpose organic fertilizer, around the perennials.
Divide & Transplant:
Mid- to late April is a great time to divide grasses and other perennials. In general, do not divide spring bloomers, like peonies, oriental poppies, and irises. Dianthus benefits nicely from frequent division. Perennials with woody roots such as aruncus, asclepias, cimicifuga, echinops and filipendula should be divided in early spring before top growth emerges. Spring is also a good time for transplanting.