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I am often asked to recommend plants for problematic garden areas during my call-in radio program or after public-speaking engagements. As a result, over the years I have developed a list of my top picks for sunny and shady gardens depending on whether the soil is dense, heavy, and clay-based, or lean, sandy, and quick-draining. Fortunately, I have experience gardening with both soil types, and so I know that each presents its own challenges and opportunities. Here are a few options for perennials, trees, and shrubs that can survive and even thrive in the trickiest soil conditions.
Dry clay is difficult for roots to penetrate
Clay particles are extremely tiny, and because they are flat they tend to pack together tightly. When soil is made up of at least 40 percent clay particles, it feels dense, heavy, and sticky when wet. As water evaporates from the soil’s surface in dry weather, a hard crust may form that is difficult for plants to break through. Cracks in the soil’s surface are another sure sign of dry clay.
‘Dark Towers’ penstemon keeps its color through fall
Name: Penstemon ‘Dark Towers’
Zones: 3–8
Size: 18 to 36 inches tall and 12 to 24 inches wide
Conditions: Full sun; dry to average soil
Native range: Hybrid of North American species
Penstemons (Penstemon spp. and cvs., Zones 3–8) have seemingly caught the attention of breeders, with many new introductions that offer outstanding flowers and colorful foliage. Among these, ‘Dark Towers’ has proven to be a standout. Once established, even in dry clay soil, this plant impresses for months on end. In early spring the show begins with the unfurling of dark burgundy foliage that retains its intense color through fall. Once it is in bloom, its tubular flowers are a favorite stop for many pollinators, including hummingbirds. ‘Dark Towers’ has attractive seed heads that develop in mid to late summer and persist throughout fall and winter. These seed heads make excellent additions to garden bouquets, but leave some stalks standing for a spectacular late-season display.
Northern bush honeysuckle is extremely adaptable
Name: Diervilla lonicera
Zoens: 3–7
Size: 2 to 3 feet tall and 2 to 4 feet wide
Conditions: Full sun to partial shade; dry to average, well-drained soil
Native range: Eastern North America
If you are looking for a clay-busting shrub, give northern bush honeysuckle a try. I have observed this adaptable native plant thriving in a variety of soil conditions and sunlight levels. It may not be the showiest flowering shrub, but its small, yellow, nonfragrant blooms are a real draw for hummingbirds, butterflies, and a variety of bees. The plant is also the larval host for at least four different moth species; it is a true biodiversity builder. In fall, the glossy foliage turns yellow, red, and sometimes orange. Although a number of recently introduced cultivars offer dramatic foliage colors, the often overlooked straight species truly needs no improvement.
Hackberry feeds birds and butterflies
Name: Celtis occidentalis
Zones: 3–9
Size: 40 to 60 feet tall and wide
Conditions: Full sun to partial shade; dry to average soil
Native range: Central and northeastern North America
Like northern bush honeysuckle, hackberry is very adaptable to a wide range of soil types, including dry clay. It also tolerates pollution, so it is no surprise that this tree is being planted more frequently in urban centers. The subtle spring flowers give way to small fruit that turn purple in fall, persisting in the canopy and providing food for a variety of bird species. The fruit is also edible for gardeners. An often overlooked feature of hackberry is that its foliage is a food source for the larvae of a variety of butterfly and moth species, including one of my favorites—the morning cloak. Trees may reach a height of 70 feet; as they mature, their bark develops a beautiful corklike appearance.
Wet clay is slow to drain and prone to compaction
Clay soil swells and becomes sticky or slippery when wet, and it holds water in the microscopic spaces between its particles for a long time. This can become problematic in regions with heavy rainfall, in low-lying areas, and in shaded areas with reduced evaporation potential. It is very important to avoid working clay soil when it is wet, since that will often cause further compaction and damage to soil structure.
Bald cypress greets autumn with a blaze of color
Name: Taxodium distichum
Zones: 4–9
Size: 50 to 75 feet tall and 20 to 45 feet wide
Conditions: Full sun; average to wet soil
Native range: Southeastern United States
If you have enough space to grow a unique specimen tree in moist clay soil, I recommend bald cypress. Reaching 75 feet or taller, this
impressive eastern North American deciduous conifer only gets better with age. The soft-textured, ferny green foliage turns a golden copper before being shed in fall. With time, the tree will develop exfoliating reddish brown bark and a wealth of interesting round cones. In wet soil it is known to develop knobby knees at the base of its roots as it matures into a breathtaking focal point.
‘Blood Brothers’ switchgrass is resilient, adaptable, and long-lived
Name: Panicum virgatum ‘Blood Brothers’
Zones: 4–9
Size: 4 to 6 feet tall and 2 to 3 feet wide
Conditions: Full sun; average to poor soil
Native range: North America
‘Blood Brothers’ switchgrass will bring color, texture, and motion to a site with wet clay as long as there is no standing water. This Canadian introduction is extremely durable and has continued to perform over many years where other plants have perished. It is attractive too, with blue-gray leaves that develop eye-catching red tips crowned with abundant, airy sprays of small red flowers. The entire plant turns a warm tan color in autumn, and the stems persist and remain upright through fall and winter. I have often observed birds picking away at the seeds well into winter.
Gray dogwood produces a bounty of blooms and berries
Name: Cornus racemosa
Zones: 4–8
Size: 10 to 15 feet tall and wide
Conditions: Full sun to partial shade; moist to moderately dry soil
Native range: Eastern North America
To attract birds to a location with wet clay soil, consider adding gray dogwood to your shopping list. I have grown and observed it in a wide range of soil-moisture conditions and sunlight levels. This tall, spreading shrub puts on multiple displays throughout the seasons. A variety of insects visit its white blossoms, which appear from late spring to early summer. The flowers are followed by white fruit that provides another food source for wildlife. As the fruit is eaten or drops to the ground, the showy red pedicels that were supporting the fruit are revealed. If that were not enough, gray dogwood provides another show in fall when the green foliage transitions to shades of red, purple, and smoky gray.
Dry, lean soil in full sun drains very quickly
Sandy soil is easy to work and does not tend to get compacted, even when wet. However, the large spaces between sand particles allow water and nutrients to move rapidly through the top layer of soil and out of the reach of plant roots. Without an ample layer of mulch, sun-baked soil with a high sand content dries out very quickly after rainfall or irrigation.
Seven-son flower is especially showy at the end of the season
Name: Heptacodium miconioides
Zones: 5–9
Size: 15 to 20 feet tall and 8 to 10 feet wide
Conditions: Full sun; well-drained soil
Native range: China
For a larger showpiece in poor soil, seven-son flower is a true standout. I must confess that this multistemmed small tree or large shrub may not be very impressive when you first come across it for sale at a nursery or garden center, but give it some time and space. As new and existing stems thicken in diameter, they reveal one of my favorite features: multicolored tan and whitish exfoliating bark. I find myself stopping and admiring the trunks in every season, especially winter. From late summer into fall the garden air is sweetened by the many clusters of small, fragrant white blossoms that develop along the tips of the branches, providing a late-season treat for a wide range of insect visitors. As the white petals are shed, pink sepals are revealed; these put on a second show that lasts for a few more weeks into autumn.
Knautia blooms from midspring through fall
Name: Knautia macedonica
Zones: 5–9
Size: 18 to 24 inches tall and wide
Conditions: Full sun; well-drained soil
Native range: Southeastern Europe
Knautia may not be the longest-lived perennial, but it makes up for this by being a nonstop bloomer and a generous self-seeder. It thrives in full baking sun and appreciates the excellent drainage that a sloped site provides. In midspring it starts sending up airy stems topped by maroon to crimson pincushion flowers, and the show continues into late fall. These flowers are constantly visited by a variety of insects, and as soon as the plant sets seeds the goldfinches swoop in to harvest them, scattering a few for next year’s crop in the process. Do some deadheading and a light cutback in midsummer for an even better display that lasts further into late fall.
Knautia may not be the longest-lived perennial, but it makes up for this by being a nonstop bloomer and a generous self-seeder.
‘Worcester Gold’ caryopteris tops its bright foliage with cool late-season blooms
Name: Caryopteris × clandonensis ‘Worcester Gold’
Zones: 5–9
Size: 24 to 30 inches tall and wide
Conditions: Full sun; well-drained soil
Native range: Hybrid of Asian species
Another reliable late-season performer is ‘Worcester Gold’ caryopteris. This small shrub rarely gets to be 3 feet tall in my garden, in part because I give it a hard cutback in late spring after its new growth begins to emerge. Compared to some other shrubs, caryopteris is very late to wake up and resume growth each spring. I use this feature to my advantage by underplanting it with small spring-flowering bulbs such as species tulips (Tulipa spp. and cvs., Zones 3–7) and crocus (Crocus spp. and cvs., Zones 3–9). These early bloomers retreat and go dormant at the base of the shrub as the canopy fills in with electric gold foliage. The leaf color does lose some of its pop in the heat of summer, but that’s when a new show begins. From late summer to early fall, vivid blue spikes appear at the end of each branch, feeding a variety of bees.
Lean, sandy soil in shade may be the trickiest condition of all
Sites with dry shade accommodate a rather limited selection of plants that are equipped to endure low levels of sunlight, moisture, and soil nutrients. Tree roots may also be present in the soil, taking up a share of the scarce resources. Plants that are able to adapt to these conditions often do so by developing strong, extensive root systems.
Striped maple thrives as an understory tree
Name: Acer pensylvanicum
Zones: 3–7
Size: 15 to 25 feet tall and 12 to 20 feet wide
Conditions: Partial to full shade; well-drained soil
Native range: Northeastern United States, eastern Canada
Striped maple is an excellent small tree for lean, dry soil. I am always amazed at the amount of shade it will tolerate and the poor, dry soil in which it can survive, despite most references suggesting that it prefers moister conditions. Unlike most maples, this species has foliage with three lobes, giving the leaves a goosefoot appearance; hence another common name, goosefoot maple. Long-hanging clusters of green and yellow flowers appear after the leaves have emerged in late spring, and these are followed by whimsical chains of winged seedpods in later summer. The foliage of this underused tree turns a pleasant yellow in autumn, and the characteristic green and white streaks on the bark make a great visual addition to the shaded understory in every season.
‘George P. Baker’ fumewort is an unforgettable spring ephemeral
Name: Corydalis solida ’George P. Baker’
Zones: 5–8
Size: 6 to 12 inches tall and wide
Conditions: Partial shade; well-drained soil
Native range: Europe to Central Asia
‘George P. Baker’ fumewort is one of my favorite perennials for the dry shade under the tree canopy of my home garden. Each spring the fine, fernlike foliage is quick to emerge as the first flowering bulbs take center stage. Soon after, the glowing dark pink to red tubular flowers become the main attraction for adoring and hungry bumblebees. Lower daytime temperatures at this time of year will prolong the display. As warmer temperatures arrive, both the flowers and the foliage of this spring ephemeral disappear underground to await the following spring. When I first researched and planted this cultivar, I read that it prefers moist, free-draining soil. My garden soil may drain well, but it is certainly not moist. The fact that ‘George P. Baker’ has thrived and multiplied over the years beneath a canopy of large trees and an understory of shrubs is proof that plants do not always read up on what growing conditions the books recommend.
‘Ruby Slippers’, a compact selection that is perfect for a small space or a large container, has even more exceptional late-season color than some of the other cultivars.
‘Ruby Slippers’ oakleaf hydrangea is compact and colorful
Name: Hydrangea quercifolia ‘Ruby Slippers’
Zones: 5–9
Size: 3 to 4 feet tall and wide
Conditions: Full sun to partial shade; well-drained soil
Native range: Southeastern United States
In a similar vein, ‘Ruby Slippers’ oakleaf hydrangea has proven to be extremely adaptable to dry sandy soil and shady conditions. Hydrangeas in general are known to be moisture-loving shrubs, but once established their drought tolerance is quite impressive. We grow a few different oakleaf hydrangea cultivars; their uniquely shaped foliage provides amazing textural contrast throughout the growing season, with a finale of long-lasting red to burgundy autumn color. A compact selection that is perfect for a small space or a large container, ‘Ruby Slippers’ has even more exceptional late-season color than some of the other cultivars, and those plants that receive more sunlight develop more-intense fall color. Cone-shaped flowers appear each summer at the end of mature stems. If you prune the stems by up to a third in early spring, the floral display will be sacrificed in favor of abundant new growth from the base of the shrub with lots of beautiful, fresh foliage.
Paul Zammit is a professor of sustainable horticulture at Niagara College in southern Ontario.
Sources:
The following mail-order retailers offer many of the plants featured in this article:
- Cold Stream Farm, Free Soil, MI; 231-464-5809; coldstreamfarm.net
- Dancing Oaks Nursery, Monmouth, OR; 503-838-6058; dancingoaks.com
- Great Plains Nursery, Weston, NE; 402-540-4801; greatplainsnursery.com
- High Country Gardens, Williston, VT; 800-925-9387; highcountrygardens.com
- White Flower Farm, Morris, CT; 860-567-8789; whiteflowerfarm.com
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