The #1 Thing Your Ferns Need to Stay Lush All Summer, According to a Garden Expert

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Ferns are unsung garden heroes. Flowers like dahlias, peonies, or roses may steal the spotlight with their showy blooms, but ferns play an important supporting role in creating a visual feast with their textured fronds and verdant green color. Planted around the base of a tree, ferns conjure a cool woodland garden, while arranged in containers with other shade-lovers, they bring lush volume.

Ferns are perennials and will live for several years; some varieties are deciduous, dying down in the fall and returning in the spring, while others are evergreen. Ferns have survived and evolved since prehistoric times, yet these plants require attention to thrive in today’s landscapes and containers. Ahead, garden and lifestyle expert Carmen Johnston shares her tips for flourishing ferns throughout the season.

Select the Right Variety

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Fern varieties are not one-size-fits-all for planting in pots versus hanging baskets versus the ground. “I tell my clients: Boston ferns are for hanging baskets and Kimberly Queens are for containers. Boston ferns have arching, cascading fronds that want to spill over an edge, and they want shade,” says Johnston.

Kimberly Queens, on the other hand, are the most sun-tolerant of the tropical ferns with upright, sword-shaped fronds that maintain their shape in pots. “The key is planting her early in the spring so she acclimates while temperatures are still mild,” says Johnston. Though they can handle the sun, Kimberly Queens need more TLC once hot summer temperatures set in. At her home in the South, Johnston likes to give the plants morning sun with afternoon shade come July and waters consistently to balance the amount of sunlight they’re receiving.

If you’re getting started with ferns after spring has passed, Johnston recommends planting containers in the shade with autumn ferns. “They are hardy from about zones 5 through 9, so they come back year after year, and that coppery new growth is beautiful all season,” she says.

For tough, dry shady plots in a landscape, Johnston suggests holly ferns (which make great ground covers). For a variety of color, try Japanese painted ferns with graphic silver and burgundy foliage. And for filling out large containers, she reaches for voluptuous macho ferns.

Grow in Suitable Conditions

Ferns thrive when planted in filtered or dappled light, or in a spot with morning sun and afternoon shade, Johnston says. She uses a light, well-draining potting mix that’s slightly acidic (around 5.5 to 6.5 pH) and with plenty of organic matter. “Never use garden soil in a container. It compacts and suffocates the roots,” she says.

Happy ferns are watered consistently and stay evenly moist. “Never soggy and never bone dry,” Johnston advises. Test the top inch of the soil with your finger or a moisture meter to see how wet or dry the soil is. “In summer heat, a container fern may need water daily. Water in the morning until it runs out the drainage holes,” she says.

Watch for Warning Signs

Ferns will display their distress. “Ferns are shallow-rooted, so they show stress fast,” says Johnston. Crusty brown tips and edges signal not enough water, low humidity, or fertilizer burn, while yellowing fronds with a mushy base and sour smell mean too much water and the start of root rot. Too much direct sunlight results in pale, bleached, or washed-out foliage. “Wilting when the soil is still moist points to root rot or a fern that is badly root-bound,” she adds.

During the summer, keep an eye out for thinning fronds. “If fronds start thinning out fast and you see little black specks like ground pepper on the leaves or the porch below, that is frass from fern caterpillars, and they will strip a fern in a matter of days,” says Johnston.

However, neat rows of brown dots on the underside of a frond are spores. “That is a sign of a healthy fern doing exactly what she should,” Johnston says.

Follow a Fertilizing Schedule

Johnston’s secret to lush ferns throughout the season is to fertilize immediately after planting. “We do not wait. I treat it as prevention, not a rescue, because the goal is a full, healthy fern all season long, not nursing one back in August,” she says. “Once a fern is stressed, you are always playing catch-up, and ferns show damage long before they show recovery.”

She follows a five-week protocol and repeats it throughout the season.

Week One: She feeds newly planted ferns one to two tablespoons of Nelson Color Star. (For larger ferns, she gives a generous handful.)

Week Two: Fertilize with Jack’s Blossom Booster, mixing and watering according to package directions.

Week Three: Water ferns with a mixture of water and Epsom salt (one tablespoon to one pitcher of water) to boost magnesium and keep leaves green.

Week Four: Feed again with Jack’s Blossom Booster to support new growth.

Week Five: Flush with plain water (which will prevent the bronzing of foliage).

Johnston repeats weeks two through five throughout the season, in addition to regular watering. Every three to four months, she gives ferns another dose of Nelson Color Star.

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Courtesy of Williams-Sonoma