This article is about Japan’s only native cycad, Cycas revoluta, the so called King Sago palm. Of course, like other cycads it is not a palm at all, but rather a member of a very ancient group of plants that predate all flowering plants and modern conifer trees. This lovely species is perhaps the most cold resistant of all cycads and yet can be grown in tropical climates as well. It can grow in either sun or shade, it is able to withstand both monsoonal rains and extended droughts, it responds well to both container culture and open gardens, and for the most part needs little care. In Japan it is called sotetsu, and has been an important garden plant for centuries here.
Cycas revoluta is native only to Japan’s southern islands and the extreme south end of the southernmost main island, Kyushu, in Kagoshima Prefecture. It’s habitat is rocky shores where it can be found growing on near vertical rock faces in full sun. This region is essentially frost free and is classified as a subtropical climate. Winters average around 10 C (50 F) in the north of its range and 18 C (65 F) in the south. Winter extremes can go to freezing or even below in Kagoshima, but this is rare, particularly along the seacoast where this species is found. Summer temperatures throughout its range average nearly 30 C (86 F) with extremes rarely getting above 35 C (95 F) due to the moderating effects of warm coastal waters.
Rainfall is high with 2000-2200 mm (78-86 inches) falling in an average year. Most of that falls in the late spring, summer, and fall, particularly during the monsoon season. The summer monsoon starts early on the southern island of Okinawa, in May usually, but is a little later in Kyushu. This season typically ends in July. August is often dry, sunny, and hot, but towards its end, typhoons become more and more common and so another peak of moisture comes at this time. Falls are drier and often sunny, but by December skies grow cloudy, rainfall drops considerably, and temperatures cool down. Humidity is the one stable element – averaging between 75-80% year round.
Coming from a place like the one just described, you would imagine that this plant doesn’t have much cold tolerance, but you’d be wrong! This cycad has been grown successfully in the warmer parts of the UK and parts of the southeastern USA that routinely get hard freezes. This natural ability to withstand cold conditions has made this one of the most versatile cycads for the open garden throughout the world. In Japan it is commonly seen in parks and next to public buildings, but rarely in private yards. No doubt this due to the ultimate size these plants can attain, which can mean up to 3 meters or more tall (10+ feet) and with a frond spread nearly as large. It is grown throughout the warmer parts of Japan far beyond its native range – clear up to central Honshu at least where it requires protection in winter. In terms of the USDA’s cold hardiness scale, it can withstand zone 8, and the warmer parts of zone 7 if winter protective measures are taken.
The oldest specimens in Japan are found near temples and shrines. Some of these can be of immense size with stems up to 5 meters long and multi-headed. Usually such long stems cannot stand erect on their own, so they will grow essentially horizontal without support. One ancient multi-stemmed specimen exists at the Glover Garden residence in Nagasaki that stands at least 9 meters tall (around 30 feet). It is held up with steel supports, taking away its beauty to some degree. Indeed, many of the truly old C. revoluta in Japan are not the loveliest to look at, but you cannot help but marvel at their age and size.
There also exist a number of unusual varieties that have atypical leaf forms that have a distorted look much like the various crested forms of ferns. Probably the best known are ones that have golden leaves or are variegated. One of the more common of these is C. revoluta v. aurea. It flushes with yellow tipped fronds, but in time these become more golden orange and eventually they brown off. This type is commonly available in Japan and can also be found on the world market. Much less common is the pure yellow flushing form, v. alba, known as kogane sotetsu in Japanese (literally meaning “golden cycad”).
The starkly yellow to whitish fronds eventually turn light green within a few months, hence allowing the plant to photosynthesize and survive. This type is very uncommon in Japan, and commands high prices even as a seedling plant. Adults fetch into the thousands of dollars. Finally, a third yellow leaf form exists that is the most sought after of them all, v. variegata. In this form the fronds are a blend of yellow and green with no definite pattern. To many western eyes these plants might even appear to be sick due to the irregular patterning, but to the Japanese they are shear beauty. If you want one you’ll have to truly drain your pocket book though!
If all of this weren’t enough, these plants can be grown as bonsai as well. The trick to dwarfing them is much like the way you would take a woody plant and make a bonsai – restrict the roots and don’t over feed them. Since cycads cannot be pruned like a typical woody plant, it is necessary to limit root growth by keeping them in undersized pots if you want to dwarf them. One problem is that this process can take many years since cycads are not what you’d call fast growing, not even C. revoluta. Fertilizer is applied only enough to keep them healthy, but not enough to let them get big. In Japan this is a common technique to keep any plant small, for example palms. The result is quite interesting. Given that this species tends to form pups along its stem, plants often end up with bizarre branching, but stand no more than a meter or less tall. Again, not for everyone, but another way Japanese growers keep this species.
The only negative thing about this species is that it, like other cycads, is poisonous if eaten. All parts of the plant contain the glycoside, cycasin. If eaten it will lead to gastrointestinal distress and liver failure. There have been cases during famine when people have turned to this species as a food and suffered horribly and the phrase sotetsu jigoku, “cycad hell”, was born. Nevertheless, this species has been used as a starch source on Amami Oshima for centuries, much like coontie, Zamia floridana, was used by native tribes in Florida. The stems are mashed into a pulp and then fermented, thus slowly removing the toxins. Likewise, seeds have been used this way in Japan’s southern islands to make a “cycad cake” called sotetsu mochi.
Moreover, crushed seeds are made made into sotetsu miso, a paste much like the normal miso made from beans, in the same area. All of these practices are considered dangerous, but to this day, these traditions persist in local areas. My recommendation is enjoy the plant without sampling a piece! Still, care is needed especially for pets that seem drawn to this plant and likely will die if they eat it. The good news is that it is not a problem for humans. Children don’t find the plant attractive due to its spiny stems and sharp fronds and even the trunk is rough to the touch, so most kids shy away.
A hardy plant in the garden with a rich history – any way you look at it, this species deserves attention.