Timely summer pruning is the key to more flowers – and less flopping – in the perennial (and annual and shrub) border. Many annuals and perennials bloom better and longer if their spent flowers are regularly pruned – a practice known as deadheading. In addition to boosting floral display, deadheading also prevents self-sowing by fecund perennials and annuals such as spiderwort (Tradescantia), garden phlox (Phlox suffruticosa), and mulleins (Verbascum).
Different plants favor different deadheading regimes. Some perennials require minimal deadheading other than a hard pruning back to their basal foliage as their last flowers fade. Among these are columbine (Aquilegia), Delphinium, most catmints (Nepeta) and Salvia, most perennial geraniums, lungwort (Pulmonaria), mountain bluet (Centaurea montana), and lamb’s ear (Stachys byzantina). Many of these will send up a second round of flowers later in the season.
Numerous long-blooming perennials – including bellflowers (Campanula), balloon flower (Platycodon), Jupiter’s beard (Centranthus ruber), Shasta daisy (Chrysanthemum × superbum), bee balm (Monarda), most Veronica, garden phlox, and daylilies (Hemerocallis) – do best with frequent deadheading of individual flowers or flower clusters. In most cases, the cut should be made just above the next bud or leaf below the spent flower(s).
Similarly, most long-blooming annuals benefit from regular, light deadheading, although heavier pruning may be necessary if growth flags in summer (as sometimes happens with diascias, sweet alyssum, and others).
Shrubby perennials that flower relatively briefly (e.g., goatsbeard and Cimicfuga) usually require nothing more than a single tip-pruning after they bloom.
Some plants are better not deadheaded, particularly if their seeds are valued for ornament (as with nigellas and shrubby Clematis), bird forage (e.g., echinaceas and rudbeckias), or self-sowing. Knowing when not to prune is also important!
Deadheading is not the only type of pruning that benefits perennials. A good early-summer (or late-spring) shearing can do wonders for large, late-blooming species with unruly habits such as asters, Joe Pye weed (Eupatorium), and perennial sunflowers (Helianthus). Left unchecked, the statuesque stems of these perennials topple under the weight of their flowers.
A far better solution than trussing them with stakes and string after they flop is to cut them back halfway in June. Shorter, sturdier, swoon-resistant plants will result. Flowers may be a bit later and smaller than those of unpruned plants, but they’ll also be abundant and upright.
June is also the ideal time to prune lanky early-blooming perennials such as moss phlox (Phlox subulata), Dianthus, and perennial candytuft (Iberis). Sheared back halfway immediately after flowering, they’ll produce fresh basal growth and possibly a few repeat blooms. Straggly stems of lavender, sage, and other woody-based perennials respond well to pruning in early spring, before bloom.
And then there are shrubs. Weigela, mock-oranges (Philadelphus), Deutzia, and other shrubs of similar growth habit should be cut back hard to vigorous new lateral shoots that break growth as the flowers fade in late spring and early summer. These new shoots will eventually provide next year’s floral display. Unpruned shrubs from this group decline into a lanky mass of leggy stems topped with old, unproductive wood that chokes out new growth.
Numerous other spring-blooming shrubs (including rhododendrons and lilacs) exhibit a somewhat different growth pattern, bearing relatively short new shoots mostly at their tips. Consequently, they generally do best with a relatively light early summer pruning, with care taken to preserve as much new growth as possible (which will give rise to next year’s flowers).
Whatever the plant – shrub, perennial, or annual – it will respond well to a post-pruning application of a nutrient-rich compost such as Fafard Natural & Organic Compost. Fertile soil and proper pruning make for happy plants (and gardeners!).