Annual Plant Maintenance
Like old friends, perennials come back each year. Also like old friendships, perennials need some attention in order to flourish.
I leave the old stems and stalks on many perennials for a little extra cold protection over the winter. Those old stalks also discourage wayward feet and aggressive weeding. However, for those plants troubled by insects or disease, dispose of their spent leaves each fall. This will help thwart fungal diseases in peonies, roses, and iris, for example.
As the soil warms in the spring, new sprouts of herbaceous perennials (those plants that die to the ground but regrow in the spring) begin to poke up. When the frosts are finished, it’s time for the gardener to get back to work.
Many perennials can now be cut to the ground or just above new shoots. If old stems are alive and showing signs of growth, trim to perhaps a few inches above the ground. Examples are asters, Shasta daisies, many sages, upright kinds of phlox, yarrow, columbine, coneflower, catmint, Sedum ‘Autumn Joy’, hyssop and many more.
Most ornamental grasses, too, are ready for a major trim. It’s easier if you first tie the old blades together with twine, then trim a few inches above the soil. A hefty pair of pruners or power trimmers helps, plus the twine makes for easier cleanup.
While you’re at it, tidy evergreen perennials and shrubs as well. Remove dead leaves and stems and clip wayward branches. You can cut butterfly bushes back hard as they regrow quickly.
Get down and dirty with vigorous spreaders and ground covers by trimming or pulling rambunctious shoots; some oreganos, mint, and verbena are examples. Vinca and ivy can be truly invasive, requiring persistence and perhaps judicious spraying.
Clear away old leaves and other mulch from around the base of plants to prevent crown rot. Give susceptible perennials like hosta a little extra space to eliminate convenient hiding spots for snails and slugs.
Prune later.Wait to prune shrubs that bloom on old or last year’s wood. This includes lilacs and some hydrangeas. Leave old leaves on bulbs such as hyacinths, tulips, and daffodils until they have dried. These leaves help nourish the bulbs in preparation for next year’s bloom.
Somewhat later in the year, I like to make another quick pruning pass at my tall, potentially floppy perennials, shearing them back perhaps a foot or so above ground. This may delay blooming a bit but the result is usually shorter, better-behaved plants. Asters, tall bee balm (Monarda), some sages, and Joe Pye weed (Eupatorium) get this treatment.
Deadheading. Once perennials are in full swing, switch to the deadheading mode. This is an ominous sounding name for cutting off old, spent flowers while leaving buds and blooms still in their prime. Hand pruners or even scissors usually fill the bill here. This helps keep the garden attractive and encourages additional, even longer bloom on perennials and annuals alike. And, you may even find deadheading to be quite therapeutic after a stressful day!
Leave old flowers on when you want them to reseed as in the case of larkspur or hollyhocks, or when you want the flowers to form seeds for birds, perhaps sunflowers and coneflowers. Some plants don’t need deadheading since the withered flowers fall off with no help, as in the case of impatiens. But, it’s no calamity if you don’t deadhead. Your garden may not be picture perfect and flowering time may be limited, but it will otherwise be just fine.
What to do with all those leaves, flowers, and stems resulting from trimming and deadheading? If they are free of disease and insects, just let the material lie for additional mulch; it’s also great in the compost pile. Either way, you’ll help Mother Nature build healthier soil.
Vera Strader is a University of California Cooperative Extension Master Gardener of Tuolumne County.