EDITOR’S NOTE: This month we are adding a new recurring column – ‘The Garden Guy’ will discuss various horticultural topics that he considers local residents may find noteworthy or that are suggested by you, our readers. WSU Certified Master Gardener and landscape designer, Bruce Bennett, is also available to answer your gardening questions. Look for his column on the third Friday of each month.

By Bruce Bennett
WSU Certified Master Gardener

An Important Perennial Garden Tip

Although many people are not aware of this, one of the best gardening tasks for you to learn about in the effort to keep your perennial garden looking well-groomed all summer is to regularly prune many of the plants. This is especially important in years with cool, rainy springs when, by this time of year, many plants can grow to twice their normal size.  Improving pruning technique and timing skills can help with many gardening issues in the landscape.  Pruning can mean anything from simple ‘deadheading’, which is the removal of the spent flower heads, to cutting plants all the way down to the ground. Pruning can have many beneficial impacts, including extending plant bloom periods and/or promoting rebloom, encouraging lush new growth, reducing plant size to improve surrounding air flow thus reducing mildew and fungal problems, to staggering plant heights and bloom times for an enhanced view worthy garden.

I think the single most important type of pruning we can do is deadheading spent flowers. Yes, it may be a boring task (and a good one to teach to the kiddos in the house or from the neighborhood who want to earn a bit of money), but, it often extends the bloom period of the plant by encouraging growth of additional flower buds. How far below the spent flower you prune depends upon the growth habit of the plant. Look at the stem below the spent flower and see if there are any new flower buds forming. If there are, prune to just above the first flower bud below the dead flower. This works well for perennials such as Black-eyed Susan (Rudbeckia hirta – see left), Cone Flower (Echinacea purpurea – see left), Shasta Daisy (Lucanthemum x superbum) and Bee Balm (Monarda didyma). When you see no more flower buds on a stem on these plants, cut the stem to the ground. This will promote new growth at the base of the plant. Although you will probably have no additional flowers for the season, you will have fresh attractive foliage. 

One more word about Black-eyed Susans and Purple Coneflowers — their seed heads attract birds. If you are interested in feeding the birds during the winter months, leave spent flowers on the plant at the end of the bloom period. You will see your over-wintering birds returning to your yard all year.  Enjoy their aerial acrobatics and insect devouring services all for the price of a few seed heads.  Be aware though that in addition to providing food for the birds, the plants may lightly reseed themselves in your garden (which is not a terrible thing) if the seed heads fully develop.  Similarly, even your basil and other herbs can benefit from such pruning.  When you see the beginnings of flowers on the top of the plants, count down three leaf nodes and prune the plant.  The two small branch buds just below the cut will grow and they, in turn, can be pruned at the same third leaf node when ready for harvesting.  More and better tasting basil for a longer growing period – who can complain?  

Many perennials, like Hardy Geraniums (G. ‘Patricia’ seen left) (not the annual summer Pelargonium that we call geraniums) and Thread-leaf Coreopsis (C. verticulata) have fine foliage and many small flowers. Rather than removing individual flowers, these plants can be deadheaded by shearing off the tops after the first bloom. You can actually remove the foliage of these plants to within 4” – 6” of the ground if you want to. This shearing helps keep the plants in their place and promotes rebloom.

Daylilies (Hemerocallis) are another perennial that can begin to look rather shabby by mid-summer. Daylilies produce only one cluster of flowers on a stem. You can remove the entire stem once the flowers have finished. On repeat-blooming daylilies, like ‘Stella d’Oro’ and ‘Adena Imposter’ among others, this will encourage even more reblooming. On daylilies that bloom only once, removing spent flower stems simply improves the appearance of the plant and redirects plant energy from seed production to tuber growth. If the foliage of a daylily begins to look really bad, you can cut it off to within 2” – 3” above the ground after bloom. This will promote lush new growth. 

Some perennials just get too tall for their space or so tall that they tend to fall over. You can reduce the size of these plants by cutting them back in spring before they bloom. Although this will delay bloom slightly, you will generally have shorter, denser plants and more flowers. This technique works well for Bee Balm (Monarda didyma), Yarrow (Achillea millefolium – see left), Coneflower (Echinacea purpurea) and Cardinal Flower (Lobelia cardinalis) among others. The technique is to cut the stems back 3 to 6 inches when flower buds begin to form.  You are probably beginning to get the idea that I think pruning perennials (and many shrubs) is a beneficial gardening task and you’d be right!  

There’s one final type of plant I want to mention before closing out this column. Some perennials are planted in our gardens specifically for fall color, like Chrysanthemums and Asters.  However, these plants can begin blooming in mid-summer if they are not cut back in early summer. Generally, the plants should be cut back by about one-half when they are 12” – 16” tall. Not only will this delay bloom, but it will also produce more compact plants with more branches and, of course, many more flowers.  Match them up with other late-blooming perennials such as Montbretia (Crocosmia crocosmiflora), Blanket flower (Gaillardia), Goldenrod (Solidago species) and Japanese Anemone (Anemone hupehensis) for late-season garden and container vignettes.  And, yes, there are a great many perennials already in your gardens that I did not mention.  Who has the space in a single article?  But, that’s why I always recommend that gardeners do some research ahead of time, say on a cold and rainy winter day or a rainy and cold springtime day. In July and August?  Not so much.   Happy gardening all!

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Contributing columnist Bruce Bennett is a WSU Certified Master Gardener, Certified Professional Horticulturalist and lecturer.  If you have questions concerning this article, have a gardening question or two to ask concerning your own landscape or want to suggest a topic for a future column, please contact him at gardenguy4u@gmail.com.