Finding the best plants for clay soil
Whether you garden in the nutrient-poor red clay of the Southeast, the calcium-combined-with-clay caliche of the West or something in between, the common denominator is that clay soil is difficult to grow in. Why? Tiny particles of clay hold tightly together, slowing drainage and limiting the amount of oxygen that can reach plant roots. You’ve seen the results—anemic-looking or rotting plants.
To amend your clay soil or not?
While you can improve clay soil by amending with organic matter, such as compost, it’s not usually a practical solution for a large area. But it might help in a smaller spot, such as around your home’s foundation, where clay has sometimes been brought to the surface and compacted during construction. The old recommendation of tilling in sand will often result in an even harder, denser mess unless you get the proportions just right. Further, simply filling a planting hole with compost creates a small oasis for the roots so they may not venture outside of the hole.
The most successful solution when you want beautiful borders but have a yard full of clay soil is to choose plants that can grow in this sticky situation. Let me introduce you to some clay-tolerant beauties that are up to the challenge.
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1. Rough goldenrod (Solidago rugosa)
End your garden season on a high note with the bright yellow blooms of rough goldenrod. Flowers start in late summer, last until frost and are a hub of pollinator activity. The species has arching yellow blooms, but one of its hybrids, ‘Fireworks’ above, is an easy variety to find and has larger 18-inch-long sprays.
While some species of goldenrod are aggressive, rough goldenrod spreads slowly by rhizomes. Clay soil can help keep it in check. Goldenrod is a versatile plant that isn’t bothered by much — even deer leave it alone. And there’s no need to fertilize: Plants grow best in lean soil.
Good to know
In a five-year trial of goldenrod species at the Chicago Botanic Garden, ‘Fireworks’ was a favorite for its heavy blooming and disease resistance.
Type: Perennial
Blooms: Upright to arching plumes packed with tiny yellow individual blooms in late summer to fall
Light: Full sun to part shade
Size: 18 to 36 in. tall and wide
Cold hardy: USDA zones 4 to 9
Source: High Country Gardens, 801-769-0300
2. Russian sage (Perovskia atriplicifolia)
If you want long-lasting color and interest in your garden, Russian sage is an excellent choice. Long, billowy stems are covered with velvety gray foliage and tiny lavender to blue blooms that create a cloud of soft color from summer to fall. Flowers last for several weeks, but the colorful calyx remains for months.
Although some plants can reach 5 feet tall, many newer introductions, such as ‘Sage Advice’ are shorter. This hybrid tops out at 3 feet. ‘Lacy Blue’ grows just 18 to 24 inches tall. Russian sage is drought tolerant and quite long-lived once it gets established. Plants grow best in full sun—too much shade and stems will flop. Although this perennial prefers well-drained soil, it easily tolerates heavier clay soil as well. Finally, deer and rabbits won’t bother Russian sage, but pollinators love it.
Type: Perennial
Blooms: Long spikes of tiny lavender to blue blooms in midsummer to fall
Light: Full sun
Size: 2 to 5 ft. tall, 2 to 4 ft. wide
Hardiness: Cold hardy in USDA zones 5 to 9
Source: Great Garden Plants, 877-447-4769
3. Ostrich fern (Matteuccia struthiopteris)
It’s easy to take ostrich fern for granted — its elegant fronds have made it a shade-garden staple for generations. It’s virtually care-free, deer and rabbits generally leave it alone and it provides beautiful texture in deep shade. Plants can even grow in full sun if they have plenty of water.
You’ll often see ostrich fern growing in drifts because it spreads by underground rhizomes. Dense clay, especially if it tends to be dry, will often slow the spread. Learn about more types of garden ferns here.
Type: Perennial
Foliage: Finely dissected upright to arching medium-green fronds
Light: Part to full shade
Size: 3 to 6 ft. tall, 5 to 8 ft. wide
Hardiness: Cold hardy in USDA zones 3 to 7
Source: White Flower Farm, 800-503-9624
4. False sunflower (Heliopsis helianthoides)
Nothing says summer like the daisy-shaped, sunny yellow blooms of false sunflower. All kinds of insect pollinators love its cheery flowers, and birds eat the seeds. While it’s related to the annual types that are mostly grown from seed, false sunflower is a short-lived perennial that easily reseeds. If you’re growing a hybrid, new plants may or may not look like the parent, but it’s easy to pull unwanted seedlings.
False sunflower grows into a bushy upright plant, and the species has green foliage. ‘Prairie Sunset’ has deep purple stems and veins, and its yellow flowers have maroon rings in the centers. Variegated hybrids, such as ‘Loraine Sunshine’, bring colorful flowers and foliage to borders and are easy to find at the garden center. ‘Sunstruck’ above has a compact habit and a deeper flower color. Though false sunflower can grow in part shade, plants flower best in full sun.
Growing tip
Variegated false sunflower occasionally produces stems with solid green leaves that tend to be more vigorous. Cut those off at the crown so they don’t take over.
Type: Perennial
Blooms: Daisy-shaped yellow blooms in midsummer to fall
Light: Full sun to part shade
Size: 1 to 6 ft. tall, 1 to 4 ft. wide
Hardiness: Cold hardy in USDA zones 3 to 9
Source: American Meadows, 802-227-7200
5. Foxglove penstemon (Penstemon digitalis)
There are nearly 300 species of penstemon, the majority of which are native to western North America and Mexico. Most prefer sharp drainage and dry summers, but foxglove penstemon and its hybrids thrive even in humid weather and denser soil. Even better, deer usually give it a pass. This upright perennial is super cold hardy and blooms for about a month from late spring to early summer with small tubular blooms in pink or white. Foxglove penstemon is tolerant of clay soil but doesn’t do well in boggy conditions.
You can sometimes buy the species from specialty native plant growers. It has green leaves and grows up to 5 feet tall, making a flowery addition to the back of the border. Its hybrids tend to be smaller, and some have burgundy foliage. ‘Husker Red’ is an old favorite with white flowers and grows 2 to 3 feet tall. ‘Dark Towers’ (above) is one of its progeny with pink blooms and even darker leaves. It grows 18 to 36 inches tall. Grow plants in full sun for the darkest foliage color.
Good to know
Foxglove penstemon’s small, tubular, nectar-rich blooms are a favorite among bees, hummingbirds and other pollinators.
Type: Perennial
Blooms: Lavender, pink or white tubular blooms in late spring to early summer
Light: Full sun
Size: 2 to 5 ft. tall, 1 to 3 ft. wide
Hardiness: Cold hardy in USDA zones 3 to 8
Sources: Prairie Moon Nursery, 866-417-8156 (species); Sooner Plant Farm, 918-453-0771 (hybrids)
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6. Goat’s beard (Aruncus dioicus)
When you plant goat’s beard, you need patience — these big plants take their time to get established. But once they reach maturity, you’ll be glad you waited for the 4- to 6-foot-tall stems topped by fluffy white plumes. Consistent moisture is key to good-looking plants, and they can grow in deep shade but won’t have as many flowers as in full sun.
In ideal conditions, plants will reseed. Goat’s beard thrives in humus-rich, well-drained soil and tolerates a mix of clay and loam well but won’t survive dense clay. One thing this perennial doesn’t like is hot, dry conditions.
Type: Perennial
Blooms: Fluffy white plumes in midspring to early summer
Light: Part to full shade
Size: 3 to 6 ft. tall, 2 to 4 ft. wide
Hardiness: Cold hardy in USDA zones 4 to 9
Source: Prairie Nursery, 800-476-9453
7. Siberian iris (Iris sibirica)
Siberian iris blooms are often found in shades of violet, but you can also find flowers in white, yellow, pink or maroon and those with solid petals or various patterns. Care is simple: Plant in spring so the roots have time to get established in a spot with plenty of sun. Too much shade and you won’t have as many of those lovely flowers. Consistent moisture is important for healthy plants, and while Siberian iris plants grow happily in humus-rich soil, they flourish in clay to boggy sites as well.
Keep Siberian iris vigorous by dividing every few years in spring as new growth is taking off. Dig plants out of the ground and split into pieces with your spade, making sure each new division has at least three leaves. Replant at the same level they were growing and water well.
Type: Perennial
Blooms: White, yellow, violet, blue, pink or maroon blooms in spring
Light: Full sun to part shade
Size: 24 to 48 in. tall, 18 to 36 in. wide
Hardiness: Cold hardy in USDA zones 3 to 9
Source: Local garden centers
8. False indigo (Baptisia australis)
When it comes to easy-care, it’s hard to beat false indigo. Plant this native perennial once and you’ll have loads of pealike blooms for years without a lot of effort on your part. You could deadhead, but then you’d miss out on the deep purple seedpods at the end of the season. Several species flower in violet, white or yellow. Newer hybrids have expanded the color palette to more unusual colors (for false indigo), such as pink and burgundy.
And while the species’ long stems sometimes flop, more compact varieties such as ‘Lemon Meringue’ (above) grow to just 3 feet tall and don't have that problem. False indigo has a big taproot that burrows deeply into the soil — even dense clay. As a result, plants are very drought tolerant but also slow to get established and a challenge to divide.
Type: Perennial
Blooms: Purple, blue, yellow, white, pink, burgundy or bicolor pealike blooms in late spring to early summer
Light: Full sun to part shade
Size: 2 to 4 ft. tall and wide
Hardiness: Cold hardy in USDA zones 3 to 9
Source: Sooner Plant Farm, 918-453-0771
9. Woodland phlox (Phlox divaricata)
The lavender-blue blooms of woodland phlox (also called wild sweet William) are a terrific way to brighten up shady borders with clay soil. Its loose clusters of five-petaled tubular blooms have a light fragrance and provide an early source of nectar for passing butterflies and hummingbirds.
Plant one woodland phlox and you’re sure to have more in time — stems root at leaf nodes and flowers self-seed. Once blooming is done, the green leaves provide a trouble-free ground cover. Most often you’ll find the species at garden centers, but there are a few hybrids. Although they’re usually the same height, they vary in flower color. Some easy-to-find varieties include ‘Blue Moon’, with loads of blue-violet blooms a bit larger than the species; ‘May Breeze’, with white flowers; and ‘Cloud of Perfume’, with a sweet fragrance.
Type: Perennial
Blooms: Lavender to blue or white blooms in spring
Light: Part to full shade
Size: 8 to 16 in. tall, 8 to 12 in. wide
Hardiness: Cold hardy in USDA zones 3 to 9
Source: Bluestone Perennials, 800-852-5243
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