The word perennial literally means returning. The leaves of perennials die in the fall when it freezes, but the plant returns from the root in the spring when the soil temperature warms up.
It is necessary to remove the spent foliage either in the late fall, or in the early spring. Cut the spent foliage right down to the mulch so that nothing is left. Many perennials provide winter interest with their dried leaves or seed heads against the snow, so we like to leave those until spring. A partial list of common perennials with winter interest is: ornamental grasses, echinacea, rudbeckia, achillea, liatris, aster, astilbe, sedum, chelone, baptisia and any others with strong stems. Do not wait too late in the spring to remove the leaves because they can mold and cause disease if left too long.
Removing the spent flowers and most importantly, the seed head forming behind the flower petals, is a technique called “dead-heading”. A plant’s whole purpose in life is to form seeds so that the specie can continue on in the cycle of life. Removing the seed heads usually stimulates the plant to re-flower in an effort to make more seeds. Stop dead-heading in the early fall so that the plant can rest and naturally prepare for the winter ahead.
Dead-heading also works to help control the seed spreading of plants. Dead-heading does not work with every plant as some simply will only re-flower once, but what an extended show of flowers for the plants that respond well to it! We recommend the following perennials that respond well to dead-heading: aconitum, alcea, aquilegia, armeria, asclepias, bergenia, buddleia, campanula, centaurea, chelone, cimicifuga, coreopsis, delphinium, dianthus, digitalis, echinacea, gaillardia, geranium, gypsophila, hemerocallis, heuchera, iris, leucanthemum, lobelia, lychinis, nepeta, oenothera, penstemon, phlox paniculata, platycodon, polemonium, salvia, scabiosa, and veronica.
We recommend that after the first season, you fertilize with a slow release fertilizer only. This is done in the spring before the weather gets hot. Usually they will specify that they feed for 6-9 months and will specify that they are for perennials and flowers. Follow the manufacturer’s recommendations for rate of application. Do not use a fertilizer with the first number in the formula (nitrogen) that is higher than 15. Please don’t fertilize the first season of installation as we applied a starter fertilizer when we installed your perennials.
Root division of your perennials can help some species to increase in vigor and will help to control the spreading and overcrowding of the clump. Typically this needs to be done every 5 years or so. You will know it is time when the plant seems to die out in the center or looks weaker than it did before. It is also fun to share the plant divisions with others or add more garden beds. Division is best in early spring before they break dormancy for most species. Peonies, dicentra and other early spring bloomers, however, are best divided in late fall.