Some gardens look better than others even when their gardeners are growing the same plants. If plant selection and cultural conditions are similar, plant grooming is usually the reason a garden looks better. Grooming is the finishing touch for perennials. And fortunately, grooming techniques, thinning, pinching, disbudding, and deadheading, are easy and fast. But grooming provides more than a tidy garden. It can change the shape of your plants, double your bloom, or produce huge, showy flowers.
Pinching creates more compact, bushier plants, prevents flopping, and ensures more bloom. To pinch a plant, start in late spring or early summer. With forefinger and thumb, pinch out the tips of the stems. From each pinched stem, two branches will grow. You can pinch again a few weeks later for even bushier plants with still more flowers, but don't pinch after flower buds are set or you'll cut off flowers rather than encouraging them.
If you aren't sure when to pinch your perennials, keep these basic guidelines in mind. For fall-blooming plants like mums, you'll need to stop pinching around the first of July so that the plants can set flower buds for fall bloom. Pinch plants that bloom in late spring or summer once or twice in early spring, so you don't risk removing the flower buds by pinching later. Experiment by pinching one or two stems on different plants, and note the results in your garden journal so that you'll know what to do the following year. But don't pinch an entire plant you're not sure it's the right time; it's better to have a leggy plant that blooms than a compact one that doesn't.
Pinching produces more flowers, but the individual flowers will be slightly smaller than those from an pinched plant. If you want extra-large, fair-size flowers, the technique for you is disbudding.
Thinning is removing some of the stems of dense, bushy plants to let the light and air circulation. This technique helps prevent mildew on susceptible plants like garden phlox (Phlox paniculata), bee balm (Monarda didyma), and delphiniums. Thin in spring by cutting or pinching out stems at soil level Thin each plant to the 4 or 5 strongest shoots, leaving 2 to 4 inches between the stems.
Like pinching, disbudding is a simple technique. Where one bud is larger than the others in a cluster, pinch out the smaller buds and just leave the largest. Disbudding will give you showy results on plants like peonies and roses. Don't use this technique on spike-blooming perennials like delphiniums and lobelias (Lobelia spp.), since a single large flower on the top of a denuded flower spike wouldn't be ornamental. However, you can pinch the smaller side spikes of perennials like delphiniums and monk's hoods (Aconitum spp.) for a larger central spike.
Deadheading is a gruesome name for a very useful technique, removing spent flowers. Some perennials deadhead themselves, dropping old flowers to the ground. But the brown, papery ruins of other flowers will spoil your pleasure in a perennial border unless you take them off regularly. Daylilies and bearded irises are prime offenders.
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Deadheading provides your perennials with more than good looks, though. It's an important maintenance technique for several reasons.
Flowers usually fade after pollination, so if you leave them on the plant, you're encouraging seed formation. This robs the plant of vigor, since it takes a great deal of the plant's energy to mature seed. By deadheading, you'll allow the plant to channel that energy back into flower, leaf, and root production.
Removing spent flowers (and potential seeds) keeps invasive perennials from self-sowing all over your garden.
Deadheading often extends the bloom season, since the plants will keep flowering rather than stopping after the first flush, as they would if they had set seed. In fact, if you shear back some plants after blooming, you'll often get second flush of bloom later in the season.
Although an attraction of perennial flowers is their perennial nature, "perennial" doesn't mean that the plants never need any care. With time, these plants suffer from age as their clumps spread outward, the old centers dying out, or inch upward and then weaken from exposure. Crown division keeps a plant young.
As soon as you see the first green shoots of an aged perennial poking through the ground in the spring, grab a shovel and lift the clump out of the earth. Shake some soil from the roots so you can see what you are doing, then start cutting apart the crown. Depending on how the crown grows and its age, use your bare hands, a shovel, a sharp knife, or hand pruning shears.
The pieces that you want to save for replanting are the youngest ones, typically those at the outer edge and having some roots attached. Replant only the most vigorous young crown pieces, first enriching the soil, if necessary with humus, fertilizers, and other amendments.
Perennials vary in the frequency with which they need division. To look their best, asters and hardy chrysanthemums require division every year. The same goes for bee balm, tansy (Tanacetum vulgarae), goldenrod (Solidago spp.), and artemisia (Artemisia spp.), not for the sake of appearances, but to keep them from spreading.
Division every 3 or 4 years is sufficient for sea pink (Armeria maritima), phlox (Phlox spp.), coralbells (Heuchera sanguinea), Canterbury-bells (Campanula medium), snow-in-summer (Cerastium tomentosum), Siberian and Japanese irises, veronica, and yarrow.
Don't be too eager to divide certain perennials. Wait until after blossoms fade to divide Oriental poppies (Papaver orientale), bleeding heart (Dicentra spectabilis), bearded iris (Iris spp.) and Virginia cowslip (Mertensia virginica), all of which go dormant by midsummer.