This spring, I wrote an article about spring ephemerals – those woodland species that flower early in the spring and then, for the most part, disappear till the following year. Summer has arrived and we have a number of shade tolerant plants for your woodland gardens that bloom through the summer and into the fall. In today’s article, I’ll talk about some of these and share some images from my shadier gardens.
Plants that grow under the tree canopy of a forest have to be tough. Not only do they need to compete with tree roots for moisture, they need to be able to collect light that filters through often dense canopies of leaves. Many of these plants collect as much energy from the sun as possible before the trees leaf out, then “coast” on that stored energy for the rest of the summer. But a few plants buck the trend and manage to grow, produce flowers and set seed under shady conditions that few others could tolerate.
One thing I have observed that almost all these plants have in common is large leaves. They require maximum leaf area to absorb the few photons of light that filter through the trees, with their leaves designed to work at maximum efficiency. (Compare, for instance, the leaf of shade tolerant Asclepias exaltata – Poke Milkweed – to those of the sunny, open prairie species Asclepias verticillata – Whorled Milkweed or of the shade tolerant Lobelia inflata – Indian Tobacco – with the sun-loving Lobelia spicata – Pale Spiked Lobelia).
Another thing I have noticed these plants tend to have in common is that their flowers are mostly white, green, pale blue or pale yellow (at least until the fall, when a few brighter colours – mostly yellows – appear). Whether this has to do with the plants requiring more energy to produce colourful flowers (speculation on my part) or because in shady areas these colours show up more for the pollinators to find, I have no idea. Two exceptions are the brilliant reds of Monarda didyma (Beebalm) – not normally associated with shade gardens, but it thrives in moist dappled shade in my garden – and Lobelia cardinalis (Cardinal Flower).
It is the end of July as I write this, and a few late-spring/early-summer shade tolerant plants have now finished blooming and are setting seed. These include Thalictrum pubescens (Tall Meadowrue), T. dasycarpum (Purple Meadowrue), T. revolutum (Waxy Meadowrue) and Asclepias exaltata (Poke Milkweed).
Monarda didyma (Beebalm) and Lobelia cardinalis (Cardinal Flower) are both in full flower right now in full light shade where they brighten dark corners with a brilliant flash of colour, and attract hummingbirds and butterflies. And new to my shade garden this year, but doing nicely, is the porcelain blue Campanulastrum americanum (American Bellflower). Lobelia inflata (Indian Tobacco, aka Puke Weed) is also flowering now in full (but relatively light), moist shade with delicate, pale bluish flowers.
Just starting to bloom in my shade gardens are Eurybia macrophylla (Large-leaf Aster), Eurybia schreberi (Schreber’s Aster), Aralia racemosa (American Spikenard), Ageratina altissima (White Snakeroot), Actaea racemosa (Black Cohosh), Scrophularia marilandica (Late Figwort) and Circaea lutetiana (Enchanter’s Nightshade). These are joined by a large patch of Impatiens pallida (Yellow Jewelweed). Even some Veronicastrum virginicum (Culver’s Root), another plant like Beebalm that isn’t normally thought of as a shade tolerant plant, is doing great under the dappled shade of Gymnocladus dioicus (Kentucky Coffeetree).
We also have some lovely plants suitable for part shade. These would normally be found at the edges of forests, and can tolerate quite a bit of shade. However, many of them tend to flower more prolifically with the benefit of more sunlight. Most books suggest that Solidago juncea (Early Goldenrod) requires full sun, but it is doing well under a large sugar maple in my yard where it gets only a half hour or so of direct, late afternoon sun. As its common name suggests, it is one of the earliest goldenrods to flower and starts flowering in my southwestern Ontario garden around the third week of July.
A number of other shade plants – mostly asters and goldenrods, but also some interesting woodland species – will start to bloom in the next few weeks but I’ll leave those for a later article. We also have lots of shade-loving ferns, grasses and sedges, and a few great shrubs for shade, but those, too, will have to wait.
Note that none of the plants listed above will thrive in deep shade such as that often found under Norway Maple, evergreens (like spruce or cedar) or close to the north side of a building, but they will all do very well in dappled shade (from less dense canopies such as under Kentucky Coffeetree) or if planted near the edge of the shade where they can get sun for at least part of the day. If you do have deep shade, you may want to consider some of our spring ephemerals mixed with ferns, for now.
Happy native plant gardening.