We treat many woody plants as if they are herbaceous perennials. That is, we ask them to grow back right from the ground every year. The reasons we do this vary with the plant species and situation, but one advantage that applies across the board is that it makes gardening simpler. "Nothing quicker than one-cut pruning," Steven says.
Janet agrees, "Yes, cut it all the way back to the ground." People new to this strategy often wonder if they heard us right, and say, "What, about six inches above ground? Or a foot?" to clarify, we say, "No! All the way down. When it's cut back to the ground you should be able to walk on it without stubbing a toe. Stubble is trouble, so make fewer, bigger cuts rather than a lot of little cuts. Stronger, cleaner growth comes from bigger cuts."
Why and What to Cut to the Ground
Here are the main objectives, with example shrubs. Sometimes we cut for one reason, sometimes for multiple reasons, but since Steven insists Janet keep this brief, a shrub like butterfly bush that could be listed under several categories is listed here just once. Steven says to, "Tell you what to look for overall then you can choose whether and why to continue to cut."
A hard cut will keep some shrubs a bit smaller than they would be otherwise. When it starts new every spring the plant may be shorter and almost always it is less wide.
Dwarf spirea (Spiraea japonica and S. x bumalda)
Purple beautyberry (Callicarpa dichotoma)
Panicle hydrangea (Hydrangea paniculata 'Limelight' et al)
Rose of Sharon (Hibiscus syriacus)
Hard cuts can improve summer color in a garden. Summer blooming shrubs that are cut hard in spring may bloom two or three weeks later than otherwise. It's the answer if dwarf spirea's pink flowers will serve you better in July than June, or you want to stall butterfly bush to better serve butterflies that fly in August and September.
Examples: Butterfly bush (Buddleia davidii)
Ural false spirea/Ash-leaf spirea (Sorbaria sorbifolia)
Creating clean, straight lines is often our goal. Branches that grow straight up from the base in year one often put all their energy into side branches in subsequent years, making the shrub bushier and eventually so tip-heavy that main canes bow outward. The whole plant becomes denser and wider. Cut back, it is more of a fountain spray.
Blue mist spirea/Bluebeard (Caryopteris x clandonensis)
Buttonbush (Cephalanthus occidentalis)
Shrubby potentilla (Potentilla fruticosa 'Goldfinger,' 'Abbotswood'' et al)
Japanese beautyberry (Callicarpa japonica)
Cut hard, shrubs and trees grown for foliage effect may produce extra large leaves and new growth with its more saturated color may continue longer into summer.
Barberry (Berberis thunbergii)
Dappled willow (Salix integra 'Hakura Nishiki')
Elderberry (Sambucus nigra, S. canadensis, S. racemosa ) (Sacrifices the bloom)
Golden vicary privet (Ligustrum x vicaryi)
Smoke bush ( i and hybrids) (sacrifices the bloom)
We do love redtwig dogwood's winter stem color. Blue willow and green kerria stems light up the dull February landscape. Traditionally, we're told to cut 1/3 to 1/2 of the stems to the ground every year but all can be cut completely to the ground.
Examples: Dwarf blue willow (Salix purpurea nana)
Golden willow (Salix alba tritellina)
Japanese kerria (K. japonica)
Redtwig/Yellowtwig dogwood (Cornus alba, C. sericea, C. stolonifera)
Some of our hard cuts aim to keep all parts of the plant young and limber, eliminating the troublesome debris that can build up in very fast growing species, shrubs that are likely to die back over winter, and those that are prickly. A tangle of deadwood can be an eyesore in any plant. The plant racks up strike two if its accumulated dried leaves and twigs provide a nurturing environment for pest insects and mites. Worst, if the twigs that die, become brittle and fall are thorny or prickly, their presence in ground litter and mulch can pose more hazard to gardeners than barbs on live branches.
Groundcover roses ('Knockout', 'Carefree' et al)
Late blooming St. Johnsworts (Hypericum prolificum, H. kalmianum 'Ames', 'Blues Festival', H. frondosum 'Sunburst')
Snowball hydrangea (Hydrangea arborescens)
Now! In late winter the growth for the season has not yet begun. Cut now, a plant won't waste stored energy in shoots you will later remove. All of its resources will go into fewer, stronger stems. Also, neighboring herbaceous perennials and bulbs are not yet up or not yet expanding. It's easier for the gardener to walk, kneel or sit.
Every year? For some yes, others maybe. We cut hard on all butterfly bushes and Japanese beautyberry every spring because we want the straight canes and clean vase shape. Barberry and dwarf spirea we cut every year in some gardens. Elsewhere we cut them hard only every second or third year depending on how quickly they become cluttered and too large.