For some reason, the fall season is when many gardeners get the itch to prune back plants in their gardens. The guidelines are as follows, at least for our zone 4 to 5 gardens here in Ottawa, Ontario:
- if a shrub blooms early (before June) wait until after flowering to prune. Some examples of early bloomers that need that old wood to bloom on are lilacs, forsythia, bridal wreath spireas, sand cherries, weigela, ninebarks, rhododendrons, viburnum, cranberry bushes, flowering dogwoods, and magnolias.
- if the shrub blooms after June, it can be pruned back in the fall or in the early spring when new growth is visible. Examples include Snowball and PeeGee Hydrangeas, spireas (except for bridal wreath), Butterfly bush, smoke tree, hibiscus (rose of Sharon), and red-stemmed dogwoods.
- woody shrubs like boxwoods, junipers, and cedars can be trimmed back in the fall too, but also throughout the growing season (spring and summer)
- some shrubs are best pruned while dormant (late fall to very early spring, late February to early March) These include barberries, smoke bush, crepe myrtles, spireas (except bridal wreath variety), dogwoods, and cotoneasters.
- to rejuvenate shrubs that flower poorly, are overgrown or straggly, cut them back to just above the first bud above the soil while the plant is still dormant. Shrubs that do well with this drastic treatment include spireas, lilacs, ninebarks, forsythias, barberry, weigela, blue mist, forsythia, honeysuckle, and potentilla (cinquefoil). You may sacrifice the flowers the first season after this rejuvenation, but the plant will be healthier.
- deciduous (non-evergreen) trees are best pruned when dormant (late winter) as well. It is much easier to see the structure of the tree before the leaves come out. Winter pruning also prevents the formation of bacteria and disease in the cuts. The wounds will heal quickly as new growth starts shortly after pruning.
- dead branches can be cut off any time in the season.
- after the first frost, remove any leaves from roses and apply mulch to the crowns. This prevents the plants from heaving from the ground during freeze/thaw cycles. You can cut the longs stems of the most tender floribundas, hybrid teas, and grandifloras back to 20 inches before winter too to prevent them from breaking off under a heavy snowfall. Another tip for tender roses is to apply a collar around the bush and fill it (loosely) with leaves. Wait to prune others back until daffodils start to bloom in the spring to ensure the ground temperature is sufficiently warm. Dead or broken branches can be cut off in the fall or any other time of the season. Suckers can also be removed in the fall, cutting them out as close to the base of the plant as possible.
Perennials can be, but do not have to be, dead-headed (remove dead blossoms) and cut back in the fall. Remove sturdy flower stalks (coneflowers etc) right back to the foliage at the base of the plant. Some gardeners like to leave these stalks on the plants over the winter for birds and their snow-covered beauty. On softer plants simply remove the browned and dead looking, limp, or soggy foliage (daylilies, peonies, bleeding hearts, etc) and cut back their stems to six or eight inches from the ground. I like to do everything I can in the fall because spring seems to be so short-lived these days and I run out of springtime hours in the gardens. Whenever you clean up your gardens, remember to harvest the seeds for future (freebie) plants as I did for my cottage garden.