Purple Cliffbrake Fern

Year-round

Purple cliffbrake is an evergreen fern that grows in fissures of dry limestone bluffs. In Illinois it occurs naturally only in the southern half of the state, well south of the Chicago area, so a Chicago planting is a garden or rock garden fern rather than a native planting here. Its documented range reaches north into Minnesota, Wisconsin, and Michigan, so it is winter hardy through Chicago's cold winters.

• Give it full to nearly full sun and a gritty, sharply drained soil. It grows naturally in bare limestone cracks, so the heavy clay common around Chicago needs extra grit or crushed rock mixed in before planting.
• Work crushed limestone or dolomitic lime chips into the soil. This fern needs an alkaline, calcium rich substrate, which sets it apart from most of the ferns native to wooded parts of Illinois.
• Let the top few inches of soil dry out between waterings once it is established. It handles drought well and is more likely to rot from sitting in wet soil than to suffer from underwatering.
• Because its natural Illinois range is limestone bluffs well south of the Chicago area, plan on managing its drainage and lime needs by hand rather than counting on the surrounding yard to provide them.

Fall

Fall in the Chicago area brings cooler, wetter weather, which suits this fern better than summer's heat. It stays evergreen, so there is little seasonal dieback to manage, but fall is a reasonable second window to plant or divide it before winter.

• Fall is a second good planting window, after spring. Cooler air and steadier rain help new plants establish roots before winter.
• Watch drainage as fall rains pick up. This is the same rot risk as summer storms, just from a different source.
• Do not cut back the fronds for winter. This fern keeps its foliage year round and does not need a fall cutback like many perennials.
• If you added mulch for a summer planting, pull it back slightly from the crown so the base is not sitting in damp material heading into winter.

Winter

Purple cliffbrake stays evergreen through the Chicago winter, and its documented range reaches into Minnesota, Wisconsin, and Michigan, so the cold itself is not a concern here. The bigger risk is wet soil that freezes and thaws repeatedly around the crown.

• No winter protection is needed for cold alone. Its native range extends well north of Chicago into colder parts of the upper Midwest.
• Make sure the planting site sheds meltwater. Repeated freeze and thaw cycles in soggy soil are harder on this fern than a hard freeze in well drained ground.
• Leave the evergreen fronds as they are. They will look slightly duller than in summer but should stay green through the season.
• Hold off on any pruning until spring, when you can see clearly which fronds were actually damaged by winter weather.

Because it stays green through winter in a tidy, low clump, it reads as an intentional planting in a front rock garden or bed edge at a time of year when most neighboring plants are bare.

Spring

Spring is a good window to plant or divide purple cliffbrake in the Chicago area, while temperatures are still cool and rainfall is more reliable than in midsummer. Established plants stay evergreen through winter, so spring is mostly about cleanup and new plantings rather than watching for regrowth.

• Plant new ferns in spring once the ground has thawed and is workable, so roots can settle in before summer heat arrives.
• Water regularly while roots are getting established, even though this fern is drought tolerant once mature.
• Trim off any fronds that browned or shattered over winter to tidy the clump and make room for new growth.
• Avoid working compost or rich topsoil into the planting area. Extra fertility works against a fern that is adapted to bare rock.

Summer

Chicago summers bring more heat and humidity than the dry limestone bluffs this fern is adapted to. Good drainage matters most in this season, since heavy summer rain on top of Chicago's clay soil is the biggest risk to the plant.

• Keep it in full sun if possible. It tolerates part shade but the color and form stay best with strong light.
• Do not add supplemental water beyond what rain provides unless there is a real drought. Overwatering in summer heat is the most common way this fern fails.
• Check that the planting spot drains well after heavy summer storms. Standing water for more than a few hours around the crown can cause rot.
• Leave the evergreen fronds in place through summer. This fern does not go dormant or dieback the way many prairie wildflowers do.