Cool, shady, tropical: that’s the look tree ferns can give your
garden. These handsome plants with fibrous trunks and plumes of finely
cut fronds aremore at home outdoors in California’s mild coastal
climates than anywhere else in the country; their growth can be
especially luxuriant where summer fog prevails. Where to plant tree
ferns, what to plant with them
All look best when planted in clusters; try setting three of them
about 5 feet apart in a triangle.
They look especially handsome planted beneath high-pruned deodar
cedars, redwoods, or other conifers. Combine them with azaleas,
low-growing sasanqua camellias, Douglas iris, liriope, campanula, ajuga,
or impatients. They also look good when planted amid lower-growing
ferns such as Boston or sword ferns.
Plant tree ferns in a wind-protected spot in bright, indirect light
or open shade (they’ll tolerate full sun in the coastal fog belt)
in loose, well-drained soil amended with organic matter.
Give them plenty of room to mature, especially when planting them
near large trees with wandering roots or under house eaves. Set ferns
in planting holes 2 to 6 inches deeper than the original soil level (if
young ferns haven’t yet developed stems, don’t bury their
crowns); roots will form along the buried part of the trunk.
To transplant established tree ferns, cut off all fronds, then dig
out a rootball about 12 inches deep and 18 inches wide. Bury the stem
(depending on the plant’s height) as much as a foot. Keep both new
and newly transplanted ferns moist but not soggy. How to grow tree
For speediest growth, feed established Hawaiian and Australian tree
ferns two or three times during growing season (April to November) with
any fertilizer containing nitrogen; fish emulsion is a favorite. Feed
established Tasmanian tree ferns in spring and fall.
Water plants once or twice a week during the summer; douse trunks
as well as root area, especially during extremely hot, dry weather.
Unlike a regular tree trunk with trunk is really a vertical rhizome,
which benefits from watering. When kept moist, it often develops more
Hawaiian tree fern (Cibotium glaucum) grows a moderate 4 to 6
inches a year, forming a 6- to 8-foot-tall trunk with red-brown hair
after 20 to 25 years. In sun near the coast, it forms golden green
4-foot fronds. Grown in shade, fronds turn apple green. This fern is
hardy to 32 [deg.] prolonged exposure to frost can burn fronds but they
usually grow back. Protect from intense sun. It’s at its best in
frost-free coastal areas (Sunset climate zones 17 and 24).
Tasmanian tree fern (Dicksonia antarctica). This is the hardiest
of the three; mature plants tolerate 20 [deg.] for short periods. Thick,
fuzzy, reddish brown scaled trunks grow slowly to reach about 15 feet
after 20 to 25 years. Dark green 3- to 6-foot arching fronds from a
fountain-shaped head. Clip dead fronds, leaving 3- to 4-inch stems.
This is a reliable grower in Sunset zones 8, 9, 14 through 17, and 19
Australian tree fern (Sphaeropteris cooperi, also sold as Cyathea
or Alsophila cooperi, or A. australis). This is the fastest grower of
the three–10 to 12 inches per year. Skinny trunks covered with coarse,
light brown scales reach 20 feet, topped by 10- to 12-foot finely cut,
bright green fronds. Established plants can tolerate full sun in the
coastal fog belt; give them light to open shade elsewhere.
Recently introduced dwarf Australian tree fern grows only 5 feet
tall with 3- to 4-foot fronds that are darker green than those of its
full-size cousin. Both are hardy to about 20 [deg.], but fronds may
burn at that temperature. Grow in Sunset climate zones 15 through 24.