Article by Houston Sanders
On Kermadec Pohutukawa
Pohutukawa: Bonsai Inspiration from Nature’s Wonders
By Houston Sanders
What’s a pohutukawa? It is the national tree of New Zealand, and one of the most interesting and beautiful tree species in the world. Imagine an old gnarled oak tree spreading its wide canopy of crooked branches from the steep bank of a rocky seaside cliff. Then imagine it completely covered in bright crimson red flowers, and you start to get the image.
A majestic old multi-trunked pohutukawa (Metrosideros excelsa).
Photo by Toni Kling. Used with permission from his art photography website Blende81 (www.Blende81.de).
Let’s start with the name: Pohutukawa. Po-Who-Too-COW-A (Easy if you try, and like many Polynesian words, kinda fun to say). In the poetic Maori language, it means “sprinkled by spray”, in reference to the trees’ preference for oceanside locations. This name refers mainly to a particular species (Metrosideros excelsa ) but there are many other species in the genus Metrosideros in New Zealand and the surrounding islands, and the name Pohutukawa is used as a general term for many of them.
The Metrosideros are fascinating members of the myrtle family, and like the more familiar myrtles, they share the characteristic of small glossy leaves, powderpuff flowers, and a very well-developed ability to produce buds on old branches. Reputedly, a Metrosideros excelsa may live to 1000 years of age. In addition, the Metrosideros family specializes in rooting. Species include the pohutukawa, the rata (Metrosideros robusta), and several smaller trees. To colonize rocky shorelines, the pohutukawa sends its roots along the ground surface, creeping over the bare rocks in search of pockets of soil. The rata often germinates high in the branches of other trees then sends aerial roots down to the ground, eventually surround and “strangling” the host tree. Unlike the popular Ficus species, Metrosideros species usually do not send out aerial roots from the branches to produce banyan style trees; they send out aerial roots from the base of the trunk. And also unlike the Ficus, Metrosideros aerial roots do not require tropical heat and humidity to form. In fact, they form very well in our Wisconsin summer climate! And these roots rapidly grow and thicken when they find a bit of soil to grow in. One can easily imagine how to take advantage of these rooting properties for bonsai!
Root-over-rock style bonsai are not commonly seen, perhaps because they are hard to grow from normal trees, and require many years of work to achieve effective results. With Metrosideros species, the root-over-rock style grows by itself!
But the Metrosideros have been woefully underutilized and are not widely available. Perhaps this is because of their climate requirements. Most Metrosideros species grow in the cool, humid climate of northern New Zealand. This is an environment somewhere between temperate and subtropical, where sub-freezing temperatures are as rare as 90° warmth. There are few, if any, places in the United States where these lovely species can thrive. So they are not available for landscape planting. But, in cool, humid Wisconsin, these climatic needs can easily be provided for bonsai - outdoors for summer and fall, and indoors or protected for the winter and early spring. Just watch out for early frosts.
Recently, a very short paragraph about Metrosideros excelsa was included in Werner Busch’s book, Indoor Bonsai. This is the only reference that I have been able to find showing the use of this species for bonsai. On a recent trip to New Zealand, I observed that few New Zealanders are making extensive use of their native species in bonsai. Most New Zealand species just grow too slowly and larger specimens do not survive well if collected from the wild. So pohutukawa bonsai specimens are rarely seen, even in their homeland.
There are two Metrosideros species that I have managed to acquire. One species is a garden/houseplant cultivar that forms beautiful glossy yellow-edged variegated leaves if given full sun. It is sold infrequently by Meehan’s nursery in Maryland under the name Metrosideros “Red and Gold”. The other is sold by Trans-Pacific Nursery, located in Washington, under the name Metrosideros villosus. A literature search showed that this tree was more commonly known as Metrosideros kermadecensis, and is native to the island of Kermadec, to the northeast of New Zealand. Both of my pohutukawas have identical appearance and growth characteristics, except for the variegated leaves. They have quarter-sized, glossy leaves and grow rapidly with a spreading habit – like a dwarf version of the Metrosideros excelsa. And, in my experience, they grow quite easily from cuttings.
Strangely, the Metrosideros’ season for fastest growth is in the fall, even as the temperatures and levels of sunlight are decreasing most rapidly. This is also the best time to repot, but there seems to be no difficulty in repotting them at almost any time of year. I have found that they like to be kept moist, with no special soil requirements except for good drainage. The aerial roots form in mid to late summer, starting from just above the soil line and creeping along the surface in search of fresh soil. As I have already mentioned, this is great for root-over-rock style, since the roots form themselves to the shape of the rock. I have had success by just planting year-old cuttings on top of rocks with a light covering of “muck” (peat and soil mix) held on by strips of panty hose (an old army trick…). The roots quickly grow into the ground, but it is best to leave the muck on for at least a year so that the roots will thicken faster. The branches extend rapidly, and it is necessary to ruthlessly cut back the new branches each fall to avoid losing the shape of the tree.
I have attached pictures of each of the two species described. Each of these trees is about 7 years old. The “red and gold” cultivar has been trained over a rock and cut back regularly as described above. The unvariegated species has been allowed to grow unrestrained in hopes of thickening the trunk and building the nebari. The trunk is now about 1 ½ in. thick, with a beautiful set of roots radiating out strongly on all sides. Oh yes, one more thing… if you choose a Metrosideros, you had better like the curves of the trunk. I am told that the name “Metrosideros” means “Ironwood” in Greek. If you don’t shape it when it is very young, forget about it!