Managing perennials in today’s mixed landscape designs has become a challenge for homeowners, as well as landscape professionals. But with such complicated plantings and diverse materials, how does one manage these landscapes to optimize the overall design? Communication with the designer is the best way to gain an understanding of how the composition was intended to work. Good designs are often orchestrated with a precision that approaches choreography; providing color and interest through all four seasons.
As a general rule, perennials are plants that live longer than annuals but are not quite as sturdy or woody as shrubs. All perennials benefit from cutting back after bloom to tidy them up and remove spent flowers; but how much to cut back and when depends on the plant type and the desired effect. For simplicity’s sake, group perennials by how they grow. There are three broad (and rather arbitrary) categories:
Crown Types: Phgelius, Echinacea, Verbascum, Salvias (rosette types):
Late summer is the best time to clean up Crown types. Cutting back crown type perennials in August/September promotes good stem and basal foliage development throughout winter. Some like Verbascum and Echinacea need winter chill on the stem primorda (newly emerging leaf buds) to promote bud development.
Herbaceous Types: Campanula, Coreopsis, Ajuga, Stachys:
Herbaceous types, both deciduous and evergreen, are best tidied up for winter in early fall. The stems of herbaceous perennials are typically soft and may be creeping, (Lamb’s Ears), tufting, (Agapanthus right) or bushy (Coreopsis). Early fall clean-up removes spent leaves, pests, diseases and built-up residue as well as preparing plants for winter with enough time to renew growth (if they’re not deciduous) and look presentable.
Root Types: Hemerocallis, Dahlias, Alstromerias, and Oenothera:
Take care when cleaning out the old foliage and flowering stems of Root types; their fragile growing points near the soil surface are easily damaged. Many root types need specialized care (Bearded Iris should be cleaned and divided, if necessary, in late summer/fall). Deciduous types (Dahlias & some Daylilies) need time to ripen foliage and store energy for next season’s bloom, so don’t cut them back until early December.
There may be no iron-clad rules when it comes to handling perennials but all good maintenance plans incorporate a thorough understanding of each plant Including how it grows and what part it plays within the garden as a whole.
Communicating with the designer, the guidelines above, combined with your own observations and experience are a surefire formula for creating the optimal maintenance plan for your garden.