Q. Will cutting spent flowers off of my perennials encourage more blooms?
A. Removing old or spent flowers is known as deadheading. Most ornamental plants benefit from deadheading; however, newly planted young plants are less likely to require frequent deadheading in their first year of growth.
There are several reasons for deadheading. Most gardeners do it because it aesthetically looks better when dead plant material is removed, such as peonies and annual pinks (Dianthus chinensis).
Deadheading can prevent self-seeding of plants that you don’t want to spread, such as clustered bellflower (Campanula glomerata). Don’t deadhead plants that you may want to spread, such as woodland phlox (Phlox divaricata) and lupine (Lupinus).
Another important reason to deadhead is to encourage rebloom and prolong the bloom period. Perennials such as tickseed (Coreopsis) usually require daily deadheading, by cutting the flowering stalk down to new lateral buds. Perennials that benefit from deadheading to prolong bloom or for rebloom include spike gayfeather (Liatris spicata), butterfly weed (Asclepias tuberosa), monkshood (Aconitum napellus), and garden phlox (Phlox paniculata).
Some perennials that will not rebloom with deadheading include astilbe (Astilbe x arendsii), siberian iris (Iris siberica), peony (Paeonia), and bigleaf ligularia (Ligularia dentata).
Later in the year, do not deadhead sturdy plants that will hold up to the heavy weight of snow because they are decorative and create nice winter interest. Also, avoid deadheading those that provide a food source for birds during the winter months.
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