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Hardy Fern Trials

Since 1992, the University of Alaska Fairbanks Georgeson Botanical Garden has conducted hardy fern trials. For nearly 20 years, we have watched a lot of ferns die or at the very least, struggle to produce one or two fronds then finally succumb. When a fern survives, we regard it with a bit of disbelief and a healthy skepticism – it couldn’t possibly last another year!

fiddle HFF trial results
phego PDF

Fairbanks is located in the central interior of Alaska (64 deg. 51 min. N, 147 deg. 52 min.W) and experiences a continental climate with some of the hottest summer and coldest winter temperatures in the state (climatic zones 1 & 2). The average annual temperature is a balmy 32F (0C), but daily temperatures can range from the mid 90s (F) in June and July to –60s (F) in winter. Despite these extremes, we are fortunate to have the moderating effect of ample snow cover. The Interior can grow a diversity of perennial ornamentals, many rated in zones 3 and 4 because snow cover buffers the temperature around the roots and crown. In Fairbanks, snow begins the first or second week of October and usually does not melt until April. 

Ferns often fail because they do not harden off quickly in the fall after a very short growing season. Many plants do not adapt to our long photoperiods, and they are actively growing when winter arrives. In addition, if sufficient snow has not fallen by the end of October, there will be a lot of death in the garden the next spring.  Of course, mulches help, but we don’t use any protection in the botanical garden choosing instead, to weed out the wimps from the truly hardy plants. Most winters are characterized by a long, cold season with an average of 50 inches of dry, powdery snow.

Even if a fern survives our brutal winter, summer conditions can prevent growth.  The average summer soil temperature in a sunny garden at a 4-inch depth is 50F. Shade gardens are colder, and it is not uncommon to dig through ice especially in organic soils. Plants may survive winter but cannot grow well because their roots are cold or encased in ice for up to half the growing season! Consequently, our list of hardy ferns is fairly small and includes mostly native Alaska ferns. The frost-free season is about 115 days with less than 10 inches of rainfall.  Short growing seasons, cold soils, and dry conditions all combine to make gardening with ferns a challenge.

shade

 Despite the small number of ferns deemed hardy in Interior, Alaska gardens, they remain very popular in home gardens and public landscapes. Hardiness trials are important, even though most plants die, simply for the list of plants that did not make it. Fairbanks, Alaska hosts many large retailers that import perennial ornamentals including ferns for Alaska gardens. The plants available for purchase have been chosen at corporate headquarters far removed from the realities of a subartic garden. Our lists, even the long “did not survive” list, provides valuable information to make better informed consumers.  These trials have also expanded our knowledge of native ferns and their ability to adapt to gardens. No doubt the list of “don’t bother” ferns will expand, but the few that survive are given a royal treatment.

Photos: Top left: Phegopteris connectilis, top right: Matteuccia struthiopteris fiddlehead, bottom right: the GBG shade house
The University of Alaska Fairbanks Georgeson Botanical Garden, PO Box 757200, Fairbanks, Alaska 99775 (907) 474-1944, gbgardensuaf@gmail.com