At times, the primary impediment to achieving an abundantly planted garden is the type of substrate. Each type comes with its own challenges, with pure clay and sand being the most difficult types to work with. Mixed or intermediate types are generally beneficial for the widest range of plants as they facilitate some drainage, yet can hold just enough water for an ideal amount of time. Clay soil, which has the finest particles and is thus the most packed, can often act as a clog in the garden.
Poorly draining, heavy clay can prevent oxygen from permeating into the lower layers of the substrate, creating anoxic conditions. It is often perceived as a low-fertility type of soil as it encourages waterlogged conditions. In wet, packed soil, roots may struggle to grow and may eventually rot. Moreover, clay soil tends to retain cool temperatures for longer; it may be exceedingly slow to warm up in spring. Under intense summer heat, it can break up into dense bricks.
Though there are a few ways to mechanically amend clay soils, it’s always possible to turn to plants for help. Some tough species, such as trees and shrubs with strong roots, are able to force their way into lower layers. This helps permit oxygen into the soil and increase drainage as well. As heavy clay soils tend to attract calcium, magnesium, and potassium particles, try to opt for plants with a high tolerance for minerals. Below are some fantastic species to cultivate in clay soil.
- Lombardo, Lisa (Author)
- English (Publication Language)
- 136 Pages - 06/29/2021 (Publication Date) - Callisto (Publisher)
1) Heartleaf bergenia (Bergenia cordifolia)
This flowering, evergreen perennial is also amusingly referred to as pigsqueak. The unlikely common name for such a pretty plant alludes to the sound that its large, glossy leaves make when rubbed together. Heart-shaped and leathery, the leaves arise as rosettes that eventually form thick clumps. These are initially dark green and turn into an enchanting purplish-bronze color in winter. For this reason, the stems are often picked and incorporated into dramatic floral arrangements.
Heartleaf bergenia flowers arise on thick stalks that grow up to 16 inches tall in spring. Dense inflorescences of deep pink-colored blooms make this species perfect for a perennial flower border. Bees and butterflies are often drawn to the blooms, which is why it is recognized by the RHS as an ideal plant for pollinators.
B. cordifolia is able to tolerate a wide variety of substrates, including clay soil. The plant seldom withers even when faced with sub-optimal growth conditions. Mass plantings of this species are known for growing quite vigorously (without being invasive) in partial shade.
2) Lady’s mantle (Alchemilla mollis)
Best for growing along the edges of clay soil patches, lady’s mantle is an attractive flowering plant with a tolerance for poor conditions. Its frothy appearance, caused by densely occurring clusters of chartreuse-colored flowers, make it a superb candidate for highly textural gardens. A recipient of the RHS Award of Garden Merit, this hardy species is one that should definitely be considered for struggling gardens.
The shoots of A. mollis grow to a maximum height of 18 inches. They produce eye-catching, palmately-veined leaves with wavy, scalloped margins. The wide leaves are known for collecting dewdrops each morning or after rain showers. These drops were once considered by alchemists as water in its purest form, perfect for use in alchemy (thus the genus name, Alchemilla).
Due to its tolerance for a wide range of substrates, this species has the tendency to become invasive. In Alaska and Oregon, it is considered a pest species. Note that it also self-seeds and can produce rapidly spreading colonies in moist conditions.
3) Japanese maple (Acer palmatum)
This stunning maple species is a small tree that thrives in shaded woodlands. It is often found in the understory layer of forests, creating distinctly dome-shaped canopies at a height of just 6 – 10 meters. This deciduous plant has three taxonomically accepted subspecies (palmatum, amoenum, and matsumurae) and dozens of cultivars. Due to its beauty as an ornamental tree, it is now cultivated across the globe.
Most A. palmatum cultivars favor partial shade conditions. They favor soils that are kept consistently moist. Though clay is not considered their primary substrate preference, there are cultivars that are able to tolerate its drawbacks. The coral bark or ‘sango-kaku’ cultivar, for example, is known for doing quite well in a wide range of soil types. This produces palm-shaped, light green to yellow leaves which turn into a pleasant salmon shade in fall.
Due to their miniature tree-like features, Japanese maples are perfect for small gardens and patio spaces. They can be grown in large pots or container gardens too. Hardy to USDA zones 5 – 9, these slow-growers are adaptable to several climate types and are known for being quite cold-hardy.
4) Roses (Rosa spp.)
Roses are known for thriving in clay soil as it is rich in minerals and organic matter. The high nutrient content is essential for increasing flowering rates. Horticulturists tend to amend clay soil even further by incorporating a mix of bark chips, compost, and leaf mold into the substrate.
This is great news for gardeners that have to deal with heavy substrates! Who would’ve thought that a beautiful rose garden could thrive in one of the most challenging soil types to work with? This doesn’t mean that rose cuttings or seeds can simply be propagated in clay without prior preparation, however. As roses are sensitive to high pH levels, it may be necessary to add sulfur-based compounds to alkaline clay soils.
For best results, create a separate bed of soil that is tailored to suit the requirements of roses. Any amendments can be applied as early as fall to give them time to permeate through the substrate prior to spring planting. Annual application of mulch is also key to keeping the roots healthy.
5) Lungwort (Pulmonaria spp.)
Lungworts are woodland plants under the Boraginaceae family. Closely related to forget-me-nots and Virginia bluebells, these flowering perennials are popular ornamentals due to their speckled foliage. Depending on the species, spots may be silver, white, or light green. Many new cultivars with impressive leaves and vivid flowers have been developed in just the last decade. Most of these are greenhouse hybrids between P. officinalis, P. saccharata, P. longifolia, and P. rubra.
Lungwort flowers are usually pink or violet just after they emerge in spring. Over time, the petals may gradually turn bluer. Blooms arise from floral stalks that are slightly taller than the foliage. They can appear as early as late winter, conditions permitting. The blooms are an important source of food for bees that appear early in the season.
Consistently moist soil is vital to maintaining pulmonaria, which are generally short-lived plants. To extend their longevity, they should be divided every few years. For best results, the soil should be kept consistently moist, but not waterlogged. Good drainage is beneficial, though these plants are known for being one of the best options for clay substrates as they favor high concentrations of organic matter.
6) Japanese meadowsweet (Spiraea japonica)
This species is known for tolerating rich, consistently moist, clay soil. Its roots are able to withstand slightly alkaline conditions as well. S. japonica makes for a beautiful, yet non-fussy, border shrub for areas with full sun exposure. On substrates with a high organic matter content, it can spread by self-seeding or by suckering. As a result, it has escaped from many private gardens and has become naturalized in several parts of North America.
Japanese meadowsweet is distinguished by its mounding growth habit. In the wild, it usually grows in riparian habitats, right next to natural water features. Its upright shrubs can grow up to 6 feet tall. Its simple, oval-shaped leaves occur alternately along wiry, occasionally hairy, stems. Pink flowers, which attract butterflies in summer, arise in clusters at the tips of erect stems.
Note that despite this plant’s tolerance for saturated soil conditions, extended exposure to too much trapped water can eventually cause the roots to decline. Additionally, as S. japonica is a member of the Rosaceae family, keep an eye out for pests that tend to attack its close relatives in your area. These include leaf rollers, aphids, leaf spot, powdery mildew, and scales.
7) Plantain lilies (Hosta spp.)
Plantain lilies are forgiving plants that can tolerate a wide variety of conditions. Though they grow best in well-draining substrates, they are able to persist in heavy clay soils as well. Known for being remarkably easy to cultivate and maintain, they are long-lived plants that can add texture and color to your perennial garden for years to come.
Some of the most popular Hosta cultivars for ornamental cultivation include ‘Captain Kirk’, ‘Earth Angel’, ‘Enterprise’, ‘Fire Island’, and ‘Blue Angel’. Obviously developed by horticulturists that just so happen to be huge Star Trek fans, these cultivars are also recipients of the RHS Award of Garden Merit.
These herbaceous plants have foliar colors that range from deep shades of green to the lightest shades of yellow. Many have stunning variegation, but just as remarkable are the spiky white to pastel-colored blooms. In general, plantain lilies grow anywhere from 6 – 36 inches tall. They can usually be grown in borders or used as ground cover species in partly shaded areas of the garden.
8) Weigela (Weigela spp.)
Deciduous flowering plants, weigela shrubs are classified under the honeysuckle (Caprifoliaceae) family. Popular species for ornamental use include W. florida, W. subsessilis, and W. coraeensis. These are known for blooming profusely each spring in USDA zones 4 – 8. A second bloom period may occur in summer – fall. Depending on the cultivar, weigela can grow as tall as 12 feet and cover a spread of up to 18 inches.
Sometimes glossy, weigela leaves tend to be oblong-shaped and are distinguished by their serrated edges, petiole color, and leaf hairiness. They range in color from deep green to purple, with fall colors being relatively insignificant. The tube-shaped, white to red blooms, which arise in a corymb formation, are five-lobed. These are pollinated by butterflies, bees, and hummingbirds, though moths have a more special relationship with the plants as their larvae tend to feed on the leaves.
Although weigela performs best in well-draining substrates, it is fairly tolerant of all soil types. It can also thrive in slightly alkaline conditions as long as the soil is kept moderately moist throughout the peak growth periods. Mature plants will benefit from being occasionally pruned as the removal of older branches can help stimulate vigorous growth and flowering.
9) Black-eyed Susan (Rudbeckia hirta)
This plant’s unique common name springs from its distinctly eye-catching blooms. Its daisy-like flower heads are set apart by their vivid yellow petals, which surround a dark-colored cone of smaller disc florets. From afar, these look uncannily like eyes. Other common names include English bull’s eye, brown betty, and yellow ox-eye daisy.
In the wild, this coneflower species is usually found growing in prairies, plains, meadows, pastures, and woodlands. As Maryland’s official state flower, it is an ideal plant to grow in native gardens located in central to eastern regions of the US. Several populations have become naturalized further west and even as far as Europe, owing to their tolerance for all sorts of environmental conditions.
Black-eyed Susan is a great annual for enhancing the pollinator profile of gardens. Butterflies quickly hone in on the flower heads and eventually lay their eggs on the plant’s hairy foliage. R. hirta serves as a larval host to several Lepidopterans in the Chlosyne genus – C. lacinia, C. gorgone, and C. nycteis. Note that despite all of these merits, this plant must be grown with caution as consumption may lead to toxicity symptoms in household pets.
10) Tartarian dogwood (Cornus alba)
If your heavy clay garden is in need of some winter interest, consider planting a few Tartarian dogwood shrubs. With stems and branches that grow increasingly blood red in color as temperatures dip, this plant forms seemingly fire-like thickets. The ‘Sibirica’ variety, or red-stemmed dogwood, is particularly tolerant of poor soils and grows at a remarkably fast rate. Note that its survival through suboptimal conditions may be compromised by warm summer temperatures.
Another recipient of the RHS Award of Garden Merit, this species is generally disease-free and low-maintenance. It is also able to spread on its own via underground suckers. If you’d like to discourage colonial spread, it would be best to remove suckers before they can firmly take hold.
Though known for its vivid stems, Tartarian dogwood does produce delicate clusters of cream-colored flowers in late spring to summer. Once these are pollinated and have developed into bluish-white berries, they are feasted on by birds. Foliage is dark green for most of the year, becoming purplish-red in fall just before they drop to reveal the fiery branches.
Another superb article, thank you!
Thank you – I’m struggling to find suitable plants for Clay Soil With Poor Drainage! (i.e. boggy in winter)