Pick up any book on perennial pruning and it will focus on fall with the cutting back of herbaceous perennials after a hard frost. Clearly this is the best time of year for an annual clean-up, but its a narrow minded approach as there is much to gain with a late summer pruning. In fact perennials respond so well to shearing in summer that fresh young foliage arrives, often in a matter of weeks, and the fall garden can be a splendid arrangement of fresh new growth. In some cases the new basal growth will mature to a point where it will remain all winter, particularly when you live in the mid-atlantic states and/or have a mild winter.

Just a few excellent candidates for this include hollyhocks, lychnis, columbine, and hardy geraniums.

Knowing when to prune a perennial can be kind of tricky. A rather simple rule of thumb is to look at the crown of each perennial and look for small signs of new growth or basal growth. In the case of hollyhocks, you may find vigorous clusters of new leaves at the base of a flowering stem. This is more often the case if you've dead headed or removed spent flowers as the plant will replace its flower to seed energy back into new growth. By simply snipping off the old flower stalk, almost to the ground, you are encouraging the basal leaves to take over.

Not all perennials are as easily cut back as hollyhock, but the same general rule applies. Perennials that produce lots of flowering stems will be ratty looking with lax branches, often weighted down by seed pods. Lift the stems and examine the crown for new growth. If there are obvious signs of fresh shoots then simply grab the older stems and clip them back to where the new growth begins. Several good examples are yarrow or achillea, hardy geraniums, veronicas, and rudbeckia.

A few perennials are rather shy to show new growth but will still benefit from a good haircut. Daylilies fit into this category. Since daylilies are not bulbs, there is no harm done in cutting them back. I prefer to cut them to the ground. It will take 2 to 3 weeks for new leaves to develop, but these fresher new leaves will not only look better now, but turn gorgeously yellow in fall and remain for a much longer period.

Exuberant perennials that fall into this category include tradescantia or spiderwort, penstemon, and astilbe. If we were experiencing a particularly dry summer there might be a slight risk of harming perennials by cutting them back severely. In a situation where the garden is dry, irrigate the newly cut back perennials to encourage new growth.

Many of our perennials are actually sub-shrubs and need to be trimmed like a shrub. These include lavender, caryopteris and santolina. Trimmed rather than cut back severely, dead inner branches can be cut out and finished flowers can be trimmed back. Rejuvenation of sub-shrubs can be achieved with a severe pruning, but this is risky and is best achieved gradually, encouraging new growth a little at a time. Caryopteris and Russian sage benefit from a late spring pruning, cutting back to new shoots that sprout low on the plant.

Some perennials are often left to go to seed, either because they attract numerous birds or they are short lived and fresh seed will ensure their return. I particularly like to leave rudbeckia and echinacea seed for finches, although I deadhead most of them as they so readily seed about. Hosta seeds are enjoyed by chickadees, so you may want to leave a few in a corner of your garden. Foxglove or digitalis is allowed to seed for a short period, any longer and I would have too much! The truly biennial types will only return with seeding and the absence of mulch greatly enhances their chances. This is also true with hollyhocks and one will often find flowering stems, heavy with seed and no sign of basal growth. I leave these plants to seed as this may be their way of saying that's all for this plant.

There is really no reason your garden should look tired, especially after such a splendid summer. Remove the tired and tatty growth now to encourage a fresh look for fall.