Cool, shady, tropical: that’s the look tree ferns can give yourgarden.
These handsome plants with fibrous trunks and plumes of finelycut fronds aremore at home outdoors in California’s mild coastalclimates than anywhere else in the country; their growth can beespecially luxuriant where summer fog prevails. Where to plant treeferns, what to plant with them All look best when planted in clusters; try setting three of themabout 5 feet apart in a triangle. They look especially handsome planted beneath high-pruned deodarcedars, 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-growingferns such as Boston or sword ferns. Plant tree ferns in a wind-protected spot in bright, indirect lightor 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 themnear large trees with wandering roots or under house eaves.
Set fernsin planting holes 2 to 6 inches deeper than the original soil level (ifyoung ferns haven’t yet developed stems, don’t bury theircrowns); roots will form along the buried part of the trunk. To transplant established tree ferns, cut off all fronds, then digout 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 newand newly transplanted ferns moist but not soggy. How to grow treeferns For speediest growth, feed established Hawaiian and Australian treeferns two or three times during growing season (April to November) withany fertilizer containing nitrogen; fish emulsion is a favorite.
Feedestablished Tasmanian tree ferns in spring and fall. Water plants once or twice a week during the summer; douse trunksas 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 moreaerial roots.
Hawaiian tree fern (Cibotium glaucum) grows a moderate 4 to 6inches a year, forming a 6- to 8-foot-tall trunk with red-brown hairafter 20 to 25 years. In sun near the coast, it forms golden green4-foot fronds. Grown in shade, fronds turn apple green. This fern ishardy to 32 [deg.] prolonged exposure to frost can burn fronds but theyusually grow back. Protect from intense sun.
It’s at its best infrost-free coastal areas (Sunset climate zones 17 and 24). Tasmanian tree fern (Dicksonia antarctica). This is the hardiestof the three; mature plants tolerate 20 [deg.] for short periods. Thick,fuzzy, reddish brown scaled trunks grow slowly to reach about 15 feetafter 20 to 25 years.
Dark green 3- to 6-foot arching fronds from afountain-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 19through 24. Australian tree fern (Sphaeropteris cooperi, also sold as Cyatheaor Alsophila cooperi, or A. australis). This is the fastest grower ofthe 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 thecoastal fog belt; give them light to open shade elsewhere. Recently introduced dwarf Australian tree fern grows only 5 feettall with 3- to 4-foot fronds that are darker green than those of itsfull-size cousin. Both are hardy to about 20 [deg.], but fronds mayburn at that temperature.
Grow in Sunset climate zones 15 through 24.