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Great Gardening by Sally Cunningham

What a great time to garden! It’s July, and the sun has come out after ample rain. The plants have exploded from their crowns, so many having rushed to flower when I was away. It’s all so beautiful.

Yet I can clearly see my next job: It is time to thin the perennials.

Thin, divide, conquer

Among gardening activities, the need to thin perennials becomes most apparent in the early weeks of summer. The plants that appeared so meek and mild-mannered in May now show their true selves, and some are just way too exuberant. Others are actually thugs.

The trouble is, many gardeners are truly gentle nurturers who don’t necessarily do what needs to be done. I have heard many sweet people admit, “I just can’t throw out anything.” Well, that can really get in the way of good design and a neat looking garden. Certain plants – picture dependable black-eyed Susans – just keep spreading and spreading. Kind Karen lets them have their way, or maybe she tries to foist whole clumps on innocent, new gardeners.

This lesson is for you, Kind Karen (and Ken): There is a time to plant and a time to thin, a time to nurture and a time to get ruthless about every plant that crowds another one. You are not being mean; you are creating harmony in the garden.

Timing is important, though. Right now it’s late to lift, divide, and transplant most perennials.

Thinning is simpler, and most of the job was for June, especially for large, spreading clumps. I always reach this stage with several of my favorite plants, including:

Cleome (Turtlehead, a wonderful native with pink flowers that look like turtle faces; great for bumblebees)

Leucanthemum (Shasta Daisy, even though contemporary cultivars don’t spread as rampantly as Grandpa’s; they are an important sunny garden element but do spread.)

Campanula (Bellflowers, several species and many cultivars; spread at varying speeds. One or two should be banned but most are an irreplaceable part of the early summer garden, and if cut back will re-bloom throughout the season.)

Physostegia (Obedience plant, notorious for not obeying the “Stay” command … “Miss Manners” is among the less obtrusive choices; beautiful late-season flower but hold it in check.)

Filipendula (Queen of the Prairie, one of my absolute favorites; makes a great, showy mass when its fluffy pink inflorescence opens, but it’s a little pushy with its neighbors.)

Rudbeckia (All the cultivars in this genus are related to Black-eyed Susans, and all are vigorous. The popular “Goldsturm” replaced many aggressive old-time plants; use them where you want a big drift, such as a back border or on a bank. Having watched the diligent Buffalo-in-Bloom volunteers fight to manage them in Niagara Square for so many years, I personally decided to garden without them, although they make a bold late summer statement.)

Not covered here are ground covering plants that you buy because you want them to spread, including many short sedums, gingers, sweet woodruff, lamiums, etc.

Here is where you practice the discipline of thinning: Where they have gone too far, rip out the sections that encroach on other plants. Dig roots too or they will immediately refill the holes. Then cut into the clump even farther. With spreaders, we are all too gentle.

The psychology of reluctance

While thinning the above-named clumps, I hear my own monologue. I love plants. I love their determination to spread and present their green leaves and flowers to the world. I remember when I bought one little Cleome, that grew into this wonderful 4-foot clump. I find it very difficult to grab a seedling by its roots and toss it. So I must recite: “It’s for the good of the whole. It’s choking that rose, hosta, new daylily.”

Then, adding to the difficulty, many plants that remain in our gardens are not worthy of the positions they hold. Often this is for sentimental reasons, not just about loving plants but because someone we love gave them to us. For design and appearance reasons, I should have pulled out all the old-time Lemon Lilies in my front bed long ago. They would be scorned in any respectable daylily society, unless they are studying heirlooms, but they came from Janet Gurley, my friend Susan’s mother, long deceased. They stay. Similarly, Grandpa’s moss roses, Mrs. Martin’s alliums, and Aunt Peg’s hellebore that is not nearly as nice as newer cultivars. Sometimes a plant is not just a plant; it’s a memory.

On the other hand, some plants simply do not deserve a position in your garden, especially if you have limited space.

Sally Cunningham is a gardening columnist.