Perennial Gardens in Autumn

Too often, perennial gardens in autumn go neglected. The enthusiasm, so urgent and robust in spring, has waned. When we think of the garden, we tend to think of life bursting forth in spring, or of the floral abundance of summer. But autumn, with its subtle beauty, has a charm all its own.

There are many perennial plants that offer interest late in the growing season.

Although this plant is a late spring bloomer (silvery-blue star like flowers that combine beautifully with Siberian Iris) it also provides an outstanding autumn foliage display. The narrow green foliage is an eye-catcher all season long and turns golden/yellow in fall. This is one of the few perennials that looks as great in October as it does in May! A favorite is x ‘Halfway to Arkansas’, a new hybrid that combines the vigor of Willowleaf Bluestar with the more graceful, finer foliage of Threadleaf Bluestar.

Gossamer blooms atop slender stalks in August and September provide a long-lasting early fall display. A delicate, fine-textured plant with a see-through look, perfect for middle or back of a border.

There are several Asters available that combine late bloom in a wide range of colors with disease-resistant foliage. A favorite is October Skies, with lavender flowers on arching stems that produce a solid mound of color around your perennial gardens in autumn.

Calamintha ‘Montrose White’, is a mass of airy white flowers from mid-summer through hard frost (added bonus: pollinators LOVE it but rabbits & deer won’t touch it!). Read more about the 2021 Perennial Plant of the Year, Calamintha nepeta.

Chelone lyonii ‘Hot Lips’ bears spikes of hooded pink flowers for many weeks around perennial gardens in autumn. The flowers are held above glossy foliage that remains attractive right up until hard frost. It will grow in sun or shade.

Showy “mums”, forced for the autumn show, are great seasonal additions but are the best thought of as annuals. However, there are also truly hardy fall-blooming Chrysanthemums that will bloom year after year. Read more about Mums.

Tall spires bear button-like black buds that open to palest pink/white fragrant bottlebrush flowers. The dark foliage is particularly stunning when combined with yellow or chartreuse foliage.

Our native Joe-Pye-Weed holds its heads of mauve-colored flowers high above the ground on 5’-7’ stems in autumn. The dwarf selection E. ‘Little Joe’ stands at a modest 3’-4’ tall and sports raspberry colored flower heads. This plant is a valuable late season nectar source for butterflies and is often covered with them.

Although this plant is a spring bloomer it bears mentioning here simply for its valuable slug-resistant foliage, which looks as pristine in September as it did in May. Once the frost hits the foliage it turns shades of red. Bonus: the rabbits & deer won’t eat it either! A great groundcover plant for difficult shaded sites.

The fluffy plumes of Miscanthus are the show-stealers but all the grasses look fabulous in the autumn. Calamogrostis ‘Brachytricha’, the lesser-known cousin of the ever-popular Karl Foerster is an autumn garden favorite of mine. Read more about Ornamental Grasses.

Huge dinner plate-sized flowers in a wide range of colors are a grand send-off to the gardening season. While it is difficult to believe that anything this tropical looking can be hardy in Wisconsin, be assured that it is. Remember, though, that it is very late to break dormancy in spring (often not showing growth until mid-June) so be patient! The exceptional Summerific® series is bred for earlier bloom, sturdy habit, and indeterminate bloom (flowering all along the stem rather than just on the tips).

Powder blue flowers over silver foliage. Highly scented silvery foliage is unattractive to deer & rabbits.

Snapdragon-like flowers bloom from mid-summer through September. ‘Vivid’ is a pink blooming form with a colonizing habit. ‘Miss Manners’ bears white flowers and is a well-behaved plant with a clumping habit.

The classic symbol of autumn in the flower border. Extremely popular for good reason. Combines beautifully with ornamental grasses.

Our native Vernonia fasciculata stands 5-6’ tall and bears clusters of purple flowers in fall that are irresistible to butterflies. Its more refined cousin, Vernonia lettermanii ‘Iron Butterfly’, has dainty thread-like foliage and a compact 24”-30” height. Learn more about Vernonia.

Herbaceous perennial plants will need to be cut to the ground before new growth begins in the spring. However, with few exceptions*, I recommend leaving perennials standing through the winter months. The reasons for this are threefold:

1. Leaving the previous season’s growth intact offers some insulation and protection to the crown of the plant and can increase winter hardiness.
2. Beneficial insects and native birds utilize the standing stems and seed-heads for food and shelter during the long, cold winter months.
3. Perennials left standing provide at least a modicum of winter interest. Their tan foliage and seed heads offer a visual reminder of the growing season.

*Exceptions: diseased foliage should be removed and destroyed to avoid overwintering pathogens that can re-infect new foliage in spring

Think of the cycle of nutrients that takes place in nature. Leaves fall and remain on the ground to decompose, adding organic matter and nutrients to the soil. While most gardeners won’t want to simply leave tree foliage where it falls, it is still possible to replicate this natural cycle.

A leaf mulcher or shredder will break leaves into small pieces, and they can then be applied as a mulch around trees, shrubs, and perennials.  Again, diseased foliage should not be mulched but should rather be removed and destroyed.

Check out our article on Fall Cleanup vs. Spring Cleanup.