UNITED STATES—Shade influences every ecosystem. Where it is scarce, some vegetation adapts to harsh exposure to sunlight. Some develops glaucous foliar color to reflect some of the sunlight. Some develops tomentum, or foliar fuzz, to shade its foliar surfaces below. Where shade is abundant, understory vegetation adapts as efficiently. Essentially, it is made for shade.
Understory vegetation naturally grows beneath larger trees and shrubbery. It is therefore more tolerant of partial shade. Some tolerates significant shade. Ferns that inhabit forest floors beneath shady redwood trees are notable examples. So are most houseplants that originated from tropical rainforest. Naturally, most live in the shade of bigger forest trees.
Not all understory vegetation is diminutive. Some Japanese maple trees can grow rather large. However, they naturally inhabit forests of trees that grow larger. Some palms begin as understory vegetation to become the tallest trees of their gardens. Their foliage simply adapts as it becomes more exposed. Banana and tree fern foliage might adapt similarly.
Home gardens are shadier than ever.
Such adaptation is an advantage now that home gardens are becoming shadier. Modern homes are taller, so produce bigger shadows than older homes. They are closer to other tall homes with comparable shadows. Fences are higher to compensate for the proximity of homes. Garden spaces are more compact, with less space that is not partially shaded.
No vegetation survives without sunlight. Understory vegetation is simply more tolerant of partial shade than most other sorts. It is adapted to it, just as some vegetation is adapted to extreme exposure. Generally, understory vegetation is deep green, to absorb as much sunlight as possible. For the same reason, individual leaves are typically large and lush.
Cast iron plant seems to tolerate more shade than any other understory vegetation. Kaffir lily and Hosta tolerate almost as much shade as some ferns. Rhododendron, azalea and andromeda prefer only partial shade. Excessive shade inhibits bloom. The same applies to camellia and hydrangea. Realistically, all species of understory vegetation are unique. Each tolerates a particular degree of shade that it is adapted to.
Highlight: Hosta
Even for some understory species, shade can inhibit bloom. For Hosta, that would not be much of a problem. Its late summer bloom is merely an added bonus to its lushly colorful foliage. Actually, the foliage is more appealing without its tall floral spikes. Such bloom is prettier in a vase anyway. The hanging white or lavender flowers are an inch or two long.
Where summer weather is cooler, some Hosta can grow three feet tall and twice as wide. Locally, only a few of the largest cultivars can grow as wide as three feet during summer. Then, they defoliate by winter. Most have broadly rounded leaves, but a few have narrow or wavy leaves. Many have paler green, yellow or white variegation, or glaucous foliage.
Hosta is uncommon here, probably because it may be somewhat demanding. It requires very regular watering to avoid desiccation. It craves organically rich soil or potting media. Fertilizer can enhance lushness but can burn foliage if just slightly excessive. Slugs and snails can ruin foliage. However, Hosta are understory plants that tolerate a bit of shade.
