The Challenge of Successfully Mixing Perennials

Coneflowers with catmint.

When people think of a garden, they usually envision a perennial garden. Perennial gardens can be a massive grouping of plants that includes everything from non-flowering ferns to shrubs like Roses and vines like Clematis, and of course, perennials. Perennials are plants that go dormant over winter and grow new from the plant's roots every spring.

Gardeners who grow perennials have a tendency to become slightly crazed. Some become addicted to a certain plant family and grow only plants of that genus, acquiring every species and cultivar. Others go to Herculean efforts to grow a particular type of perennial not suited to their area. All perennial growers become opinionated in their likes and dislikes.

Developing a perennial garden can be a challenge. Perennials are expensive to purchase, but in a few years gardeners frequently have so many, they dig them up and give them away.  Many perennials have short blooming periods that leave the garden filled with ugly foliage. Some perennials, like Asiatic poppies, disappear all together leaving a barren hole in the garden. Gardeners often place perennials with dramatically different growing needs in the same garden, ensuring some plants will fail to grow. Often the end result is a perennial garden that seems more a green space than a flower garden.

Like many amateur gardeners, I seem unable to resist a perennial sale. The urge to find some new cultivar, or something not grown before, is part of the fascination. I've learned as much from plant failures as successes.

Mixing plants is part science and part art. The science part is mixing plants that have similar growing needs. Checking the plant's nursery label or a good garden book helps eliminate the problem of knowing a plant's requirements. The art part enters in the mixing of plants. The intent is for the garden to have a succession of blooming plants, while ensuring plants that bloom together harmonize with each other. Usually I need to grow a plant for one season to learn the time of bloom in my area and how well it mixes with other plants. Once familiar with the plant, I move it to the best placement in my garden.

After many disappointments, I now experiment watching for the plants that look best the longest in my garden.  I have developed a list of characteristics for my perennial plant purchases.

Number one is interesting foliage that stays attractive for the whole growing season. The foliage is part of the garden for much longer than the flowers. Hosta, Sedum, Dianthus, Heuchera, and ferns are a few good selections. Siberian iris (Iris sibirica) also have season-long attractive foliage as do the low-growing Moss Phlox (Phlox subulata) and some of the Salvias.

Siberian Iris

The Second is hardiness and care needed to keep the plant attractive.  At the cost of perennial plants, it seems thrifty to grow ones that can survive harsh winters, humid summers and our generally unpredictable weather.  A plant can also be too hardy and become a rampant weed,  like Creeping Buttercup. While I love Daylilies and Shasta Daisies, I hate the deadheading needed to keep the plants attractive. Others need staking.

Third is the length of the blooming season.  The Sedum Autumn Joy, while blooming in the fall, carries light green flower heads for a long time during the summer. Coreopsis verticillata combines beautiful thread-like foliage and near summer-long bloom. Some of the Achillea, Campanula and Geraniums also have long blooming times.

Fourth is beauty of the bloom, which sometimes suppresses all the other characteristics. Which is why I have done a lot of deadheading on some very short-season plants like Iris and Daylily.

So my advice? Mix it up and see what happens. Make your garden pleasing to you,  And as you plant your perennials sternly tell them, "Don't sink your roots too deep. You'll most likely move in a year or two."