With grass growing slower due to less daylight and somewhat cooler temperatures, and fertilization not needed in the lawn and landscape, landscape managers with more time on their hands undoubtedly are tempted to prune back summer perennials and ornamental landscape shrubs such as roses and crape myrtles.
Many perennials, such as hibiscus species, hydrangea, salvia species, firebush (Hamelia patens), rudbeckia, echinacea, lantana (sterile dwarf) that are meant to die to the ground each winter look ugly and decayed after the first frost. When landscape professionals are faced with wilted leaves, seemingly dead branches and lack of flowers, the temptation is to prune them to the ground. That action might be a mistake.
Hamelia patens. Dormant now but wait until February to prune back. Image Credit: Matthew Orwat
While it may be advantageous to remove dead tips from frosty die back, cutting the plant to the ground in late fall or early winter will remove stored energy for regrowth in the spring. Instead, wait to cut perennial stems to the ground till the starches have fully translocated to the roots and the stems die. This usually occurs by February, but may occur earlier. An easy method to determine this is to scratch the stem. If there is no green or yellow tissue under the epidermal layer, the plant is likely fully dormant and ready to prune back.
If your client can stand to wait, allow the stalks to remain until February. If they contain any plant nutrients, this will give the plant some energy during the winter months. When practical, follow this practice to encourage stronger flowering perennials next season.
Regarding spring flowering shrubs, methods vary depending on species. They typical rule of thumb is to prune after flowering for shrubs that bloom before May to avoid reduced flowering.
With roses, it is tempting to severely prune unsightly stems and leaves now, so the plants will look orderly and manageable. While this may make the garden more attractive now, it may cause your plants trouble. Roses pruned in early winter may regrow during bouts of warm weather. This new growth will be killed by freezing temperatures, likely before flowering occurs. Also, plants will have expended energy so spring growth will be reduced, dieback may occur, and disease may set in.
Roses will look ragged this time of year, but heavy pruning now will sacrifice spring bloom and may induce disease. Image Credit: Matthew Orwat
Instead, wait to prune roses in February, or when daytime temperatures reach 70oF for 4-5 days in late winter. This will give the plants time to translocate nutrients to the roots, and once pruned, give a more bountiful display in the spring.
Azaleas follow a different rule for pruning. They need to be pruned after the spring bloom. Pruning now or before the bloom will eliminate the bloom for the 2016 season. Instead, they need to be pruned anytime between cessation of flowering until June.