Platycerium bifurcatum, commonly known as the staghorn fern or elkhorn fern, is a modestly cold hardy subtropical epiphyte native to eastern Australia and parts of the the East Indies. Though no species of the genus Platycerium can be called truly cold hardy, this species is capable of handling temperatures down to 27 F (-3 C) with minimal damage. This article chronicles a plant I’ve grown in my yard in southern Japan for the last 11 years – a climate that has tested the boundary of its cold resistance many times.
P. bifurcatum is without a doubt the most commonly propagated member of this relatively small genus of epiphytic ferns (~18 known species). Like many ferns, these grow two types of fronds, fertile and infertile. The fertile fronds are elongate, leaf-like and bear spores, while the infertile fronds (also called shield fronds because of their flat, spreading habit) have no spores. In P. bifurcatum the fertile fronds are forked (bifurcate), looking like a deer’s antlers. The shield fronds grow more or less flat against whatever they are mounted on, and are roughly circular in shape. In time plants can form formidable clumps, spreading by “pups”, or offshoots that grow off small stems (called rhizomes), just below the shield fronds. Large clumps can grow to nearly the size of a small car!
P. bifurcatum is the most commonly available cold hardy staghorn fern. Only one other species is perhaps even more cold hardy, that being P. veitchii, which is said to handle 25 F (-4 C) without suffering. P. bifurcatum is reliably cold hardy down to 27 F provided that any given frost event is not terribly long, and the following summer is long and warm enough to allow it to recover fully. It can even take down to 24 F (-4.5 C), but events like this must be very sporadic, or the plant will not be able to recover.
I moved to my current house in the fall of 2004. It is situated on the edge of some moderately tall mountains (up to 3000 ft, or 900 m elevation), and is approximately 3 miles (~5 km) from the sea. The region rarely sees below 27 F, but can get down to 23 F (-5 C) on occasion. Winters are relatively short, starting in earnest by mid to late December, and finishing by late February. During this time frosts are frequent, but usually last no more than a day. Average temperatures during this period normally are 43-45 F (6-7 C) overall, with highs around 48 F (9 C) and lows just above freezing. Winter rain is frequent, but usually light to moderate. Snow is also common, but short lived, normally melting within a few hours of accumulating.
By contrast, both spring and fall are long and mild. The frost free months extend from early April through late November or early December. Spring is followed by a strong summer monsoon, lasting from early June to late July. Temperatures during this period are warm, averaging around 77 F (25 C), and most days are cloudy with at least some rain. From late July through mid September is the real heat, with daily highs averaging between 90-93 F (32-34 C), and lows only down to 79-83 F (26-28 C). This is a time of true tropical heat.
I mention all of this to give a context for describing how P. bifurcatum has performed in my garden over the last decade. Based on my results, you can get an idea of whether your climate will be suitable to try this one outdoors or not. I will add that my plant has received no special winter protection, not even from snow. So lets see how it has progressed through the years, and what setbacks it has also endured.
The plant started in fact as two distinct, sub-adult plants bought at a typical garden shop. In the summer of 2005 they were mounted onto a crape myrtle tree (Lagerstroemia indica) into a ball of sphagnum moss, pine bark, and other organic debris. This was contained by a chicken wire net formed around the trunk of the tree. By the fall of that year the two had established nicely, but remained separate (Figure 1, top left). December 2005 had a cold start, with temperatures reaching to as low as 24 F (-4.5 C) on a couple of occasions. Fortunately, the rest of the winter was fairly normal, with frosts above 29 F (-1.5 C). Nevertheless, the newly established plants were severely damaged, looking quite bad by the following spring. They managed to squeak through the next summer, increasing slightly, and thankfully the winter of 2006-07 wasn’t very cold.
Much to my surprise, during the next spring and summer the two plants exploded into growth, and by fall had completely colonized the entire ball of growing medium (Figure 1, top right). The winter of 2007-08 again proved to be rather cold and snowy with temperatures down to 27 F on a few occasions, and there were several significant snow events. Again, by spring the plant looked rather sad, with most of the fertile fronds in bad shape. I was beginning to wonder if this species was a good garden candidate for this climate.
Then the plant surprised me again by exploding into growth and becoming an even larger ball of fronds by early fall 2008. This growth pattern continued into the next growing season and by 2009, the plant was solidly established and getting positively large, a good 5 ft (1.5 m) across (Figure 1 bottom). By now my confidence in the fern’s ability to handle local winters and rebound each summer was growing. I thought I had found the perfect subtropical epiphyte for my garden. Every person who saw it was intrigued by this most unusual plant, and many commented “your garden looks like a jungle!”
This pattern of growth continued for the next six years, even through the dreaded winter of 2010-11, which killed many of my other subtropical plants – Platycerium superbum, several epiphytic orchid species, and even Cyathea australis (a “cold hardy” tree fern). That winter was brutal not because the lowest temperatures were severe, but rather that frosts were essentially daily events throughout January, with the average temperature for that month coming in at only 37 F (3 C). Remarkably, the P. bifurcatum just sailed on with a few frost burned fertile fronds. That convinced me this plant was indestructible. I even stopped photographing it, since by now it seemed a permanent feature of the garden. Then January 2016 changed everything.
The fall of 2015 was unusually warm and frost less up through Christmas. January started out warm as well such that quite a few plants remained in flower, particularly in the city’s heat island. I even remember seeing bougainvillea in flower for the first two weeks after New Year’s. Then starting on January 24th temperatures plummeted below freezing and remained there for the next 40 hours. The first day was the worst, quickly dropping to 24 F and staying below 30 F for nearly two days straight. Moderate snow fell throughout the region, leaving accumulations up to 4 inches (10 cm) in my area. Interestingly, on the 24th there were white out conditions due to high winds, so the storm was categorized as a blizzard. In the end it wasn’t the snow that mattered for the tender plants, but rather the nonstop below freezing conditions.
At first I thought that maybe everything would be OK since many plants had lived through the long cold spell in 2011. A few days after the temperatures returned to normal the truth was revealed – many plants had taken a serious hit, and many more would likely die outright. My now huge P. bifurcatum was hit hard, as evidenced by the death of essentially all of its fronds (Figure 2). I had to wait another 2 months for spring before I knew whether it would recover or not.
At first the plant grew just a few new fertile fronds, but no new shield fronds. By the end of the summer monsoon (mid July), I began to worry about its health. I had already removed all the dead fertile fronds earlier in the spring, but the dead shield fronds remained (Figure 3, left). Fearing that they were causing harm, I removed as many of them as possible in the hopes of better air circulation in the fern’s root ball. The plant grew very little in August through mid September. Starting in late September and continuing for the next two months it began to grow more and even grew new shield fronds – a good sign. By early December it was looking much better, but still in recovery (Figure 4).
So what’s the take home message? Simply this, if you live in a climate that stays above 27 F most of the time and the average monthly winter temperature doesn’t go below 41 F (5 C) or so, you have a good shot at growing this species outdoors without much, if any winter protection. However, if frost events are common (meaning more than once a week), your chances of succeeding are less likely. On the other hand, if you live in a climate that gets occasional hard freezes (such as north Florida), but otherwise has high average temperatures, you can grow this plant, though you will need to protect it from frosts below 24 F or risk loosing your fern. In mild, relatively frost free maritime climates such as parts of the British Isles, coastal northern California and Oregon, or in city heat islands in otherwise cold climates, this fern may persist for several winters – as long as there is no serious cold event.
I would feel remiss if I didn’t mention a couple other important details about growing this fern successfully, even in warmer climates. First of all, this fern will not tolerate soggy roots. For that reason I do not recommend growing it long term in plastic pots, especially if the compost is old. Following that, the compost should be fully draining, yet moisture retentive. Soggy roots is a common reason why people fail with this plant. If you are growing this plant on the edge of its cold tolerance, I highly recommend keeping it just moist enough to prevent it from withering. A combination of cold with a wet root ball is a probable death sentence. That said, my plant has endured many rain and snow events and survived (Figure 5).
Fertilizer should be applied only in warm weather, and shouldn’t be too strong. I would recommend a slow release pelleted type with relatively low N-P-K, or any good organic fertilizer. Some folks recommend banana peels tucked into the shield fronds. I use pelleted organic fertilizer with an N-P-K around 5-5-5. Once a month is enough to keep this fern happy, backing off in the fall as the cold weather approaches.
If you follow these basic guidelines, you will be surprised at this subtropical fern’s cold hardiness and vigor. Without a doubt it will add a very tropical look to your garden. Large specimens mounted on a tree can be real show stoppers. One added benefit – these ferns are fast growing and cheap, so why not give this staghorn fern a try?