Hartley Magazine

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Hot Ferns for Cool Greenhouses

Ferns are the duct tape of garden design—they visually connect all other disparate plants. That’s why floral designers feature ferns in bouquets. And they perform the same function when you’re staging plants this winter in your greenhouse.

To find out which ferns thrive best under glass I called on my friend Judith Jones, the owner of Fancy Fronds in Goldbar, WA. She’s my go-to source for all things fern. I caught up with her by phone on her way to the San Francisco Airport to meet Martin Rickard, English author of The Plantfinder’s Guide to Garden Ferns. They planned to spend time examining specimens in the wilds of Oregon’s Siskiyou Mountains. These fern folks have way too much fun.

Cool vs. Warm

First, Judith gave me some practical glasshouse tips. Ferns—and houseplants in general—do best in cool (40 to 50 degrees) situations. Wintertime’s progressively lower light levels and shorter days signal most plants to stop growing. However if you provide too much warmth and humidity—conditions where we are most comfortable—they won’t rest. The resultant growth is often soft. A tasty meal for enterprising bugs and fungi. So keep plants cool, Judith says. “They’ll look good—just don’t ask them to grow.”

Circulate air with fans throughout your greenhouse. This lowers the humidity—a good thing (less fungi)—and allows plants to dry off. Judith says this drying toughens the plant cuticle, making them more resistant to diseases.

And there’s an aesthetic bonus. “With air movement,” she adds, “you can place your plants closer together.” That crowding will enable you to make fuller and more beautiful displays.

Best Ferns for Success

Judith suggests you seek out evergreen ferns with substantial waxy foliage. Here are several of her choices. Use repetition of the same kind for design impact.

  • Dwarf holly fern (Cyrtomium caryotedium) grows 12- to 15-inch light green fronds with serrated edges.
  • Hart’s tongue fern (Asplenium [or Phyllitis] scolopendrium) shows off upright strappy fronds—an excellent contrast to the lacier ferns. An unusual form, A.s. ‘Undulatum’, puts out wavy edging that spirals around the central stipe.
  • Long-eared holly fern (Polystichum neolobatum) displays erect two-foot dark green glossy fronds with lighter green undersides.
  • Tassel fern (Polystichum polyblepharum) has dark green lustrous fronds, to two feet tall. Best known for its springtime golden bristles.
  • Tasmanian tree fern (Dicksonia antarctica) has six-foot arching fronds, and eventually, a woody trunk for high drama in a larger greenhouse.