Ponderosa pine bonsai-a walk on the wild side
By Andrew Smith

Everybody has a favorite species for bonsai. Mine is ponderosa pine. Part of the reason for this is just convenience, for as a forester I work with ponderosas on a daily basis, and the shape, smell and feel of a ponderosa has become like the touch of an old familiar friend to me. But beyond this, ponderosa pine have some magnificent characteristics for bonsai. To get to the heart of the matter, ponderosa pine, especially old ones, have an undeniable, unmistakable character.

Ponderosa pine is one of the most common and widely distributed coniferous tree species in the western United States. It is also one of the most commercially important. Ponderosas can be found in every state from the Dakotas west to the Pacific Coast, and south all the way down into Mexico.
Ponderosa pine evolved through the eons with wildfire playing an integral part in its environment. In fact, ponderosas are one of the most fire resistant tree species in the world. It owes this fire resistance to its thick bark (which on a hot summer day smells like butterscotch), and, handily, makes for an especially handsome bonsai.

There are three subspecies of ponderosa. The most widely distributed is pinus ponderosa scopulorum. This is the species that is found over most of the western United States. It's the ponderosa pine that most people are familiar with, a three needled pine with bark that turns a luminous golden-orange as the tree ages. On the Northwest Coast pinus ponderosa ponderosa grows. In the humid climate of the northwest this species can grow 200 feet tall and reach eight feet in diameter. Needles may be up to 14 inches long. In Mexico and the mountains of Arizona and New Mexico pinus ponderosa arizonica grows. This subspecies is a little different than the other two, having needles that come in bundles of five, smaller cones, and a distinct appearance.

In the area where I live and work, that is, Eastern Wyoming and Western South Dakota, ponderosa pine can be found growing at elevations of about 3000' to about 8000'. Below 3000' the soils tend to be alkaline prairie soils and the forest gives way to sagebrush and open plains. Above 8000' the forest changes to lodgepole pine, limber pine, engelman spruce, subalpine fir and other higher elevation species.

I first became interested in bonsai through working on a research contract for the U.S. Forest Service, trying to locate and collect core samples from 400 year old and older ponderosa pine in western South Dakota. The core samples were being used to reconstruct the drought and fire history of the region for climate studies. In the process of this work, I began coring the stunted seedlings I found up on rocky ridges, so I could make some estimate of the amount of time it was taking mature trees on very poor sites to reach a height of 40 inches, which is the height I usually took core samples at. To my amazement, these stunted little seedlings were not 20, 30 or even 50 years old. Many of them were 150 years old and even older! It was from my fascination with these ancient, little twisted trees that my love of bonsai first sprung.

Of course, it wasn't long before I collected one of these estimable old ones and put it in a pot. I don't know if it was my previous work as a treeplanter, dumb luck, or some good advice I received from a travelling bonsai expert (and I have received an enormous amount of good advice from bonsai people), but despite doing almost everything wrong I still have that little tree. More than likely, it was just the toughness of the species itself. Ponderosa pine thrive under every condition from the rain and mists of the Pacific Coast, to the scorching heat of the Arizona deserts, to the -40 below winters of the northern Great Plains. From loamy valley floors to lightning scarred rocky ridgetops, through fires, droughts and floods, this tree is a survivor.

Collecting ponderosas, and other species for bonsai, is legal on most National Forest, National Grassland and Bureau of Land Management land. A pay per tree permit is required and regulations differ from locale to locale, so a little research will be in order before you go. Local ranchers may also allow collecting, if they are asked first. However, if you don't ask first they may fire a warning shot through your forehead and put a quick end to your adventure. It is almost never legal to collect anything in National Parks, Monuments, or Preserves.

I have collected many, many ponderosas since that first tree. I am often surprised when I read in books that collected trees will not be able to fit into a bonsai pot until several years after they are collected. The trees I collect go immediately into bonsai pots. This is because trees collected in the mountains are not dug from the ground, they are pried from the rock, usually with a crowbar.

In fact, rock seems almost necessary to the development of a good, wild bonsai. A tree growing on a rock will have a shallow, spreading root system that is perfect for bonsai. The same tree growing in the ground will often have a bad reverse taper to the trunk and disappear into the soil as much as six inches before roots appear.

Rocky growing sites also force the roots to stay contained in a very small area-a sort of natural bonsai pot. Usually a wild ponderosa will be anchored to the site by one or more thick roots that go directly into a crack in the rock to hold the tree in place. If you are lucky, there will also be a stiff mat of small feeder roots growing in a shallow hollow, filled with decayed pine duff, gravel and soil. It is these small feeder roots that gather most of the nutrients and water for the tree. Unlike a tree that has been growing in soil, the rocky site will force these roots to remain clustered right around the base of the tree. If there are enough feeder roots to support the tree, then the anchor roots can be safely cut off and the tree can be taken home and planted in a pot. The duff that the roots are growing in will need to be slowly removed over the next several years.

A rocky site also does a few other things for a potential bonsai. Since the root mass is contained in a very small area, the tree will only get water when conditions allow. In our area temperatures of 90-105 F are common through the summer months, humidity hovers between 15-30%, and it may go for many weeks between rain showers. As a result, ponderosas collected from a rocky ridge may have needles averaging one and a half inches long, and I've seen ones with needles as short as an inch, while the same trees growing at the base of the hill may have needles three to five inches long.

In addition, clinging to life for a century or more on a windswept rocky ridge will give a ponderosa an unmistakable character that is hard to duplicate with any amount of training. Ponderosas seem to reflect this fight for survival better than most of the other mountain species I collect. These trees have been tormented by the wind, eaten by mountain goats and porcupines, scarred by rockslides, scorched by lightning fires and beaten by hail. They have survived it all, and as a result they express the ineffable charm and individuality that only a long and fierce struggle for existence can make visible. They twist into unimaginable shapes, defying every rule of bonsai, and yet, they are still beautiful.

This harsh struggle for existence, with its associated slow growth, may be responsible for some of the great ages attained by these dwarf trees. Paradoxically, healthy trees on good growing sites usually do not live nearly as long as the stunted trees that cling to existence on the edge of a cliff. This leads to an even stranger paradox when you're collecting bonsai on a rocky site-that quite often the smaller a tree is, the older it is (within limits). The larger trees merely got started in a better microsite, and have been growing faster as a result. I don't know why slow growth adds to tree longevity, but I wouldn't be surprised if it had something to do with very dry soils inhibiting root rot. It would be interesting to know. The oldest known ponderosa in this area, by the way, is about 735 years old, and was found by my wife, Judy. In other areas ponderosas have been documented over 1000 years old.

Most collected ponderosas are planted in a very coarse growing mix. I use a turface-like clay product mixed with 30% crushed pine bark. Some growers prefer decomposed granite. Whatever is used, the mixture should allow free drainage and encourage rooting, while still absorbing some water. I water my trees when the soil in the pot is dry a half inch down. Where I live this means every two or three days in the summer, but in some areas it could be considerably less.

( Note to readers: Since writing this I have changed my watering schedule somewhat. I am now using a bigger particle size (pea size) for the soil mix and watering every day during the heat of the summer.)

I give my ponderosas as much sun as I can, but I live in a wooded area. In my climate they will grow equally well in full sun or under a partial canopy. Ponderosa pine do well as bonsai throughout the United States. But when you consider the amount of solar radiation that's available at 5000 feet under a clear western sky, you can easily imagine that to thrive in the East, or where conditions are hazy, they will need as much sun as is possible.

For winter care I keep all my trees on the ground in an unheated greenhouse. The temperature seldom goes below zero, and I heat it above 40 F in the fall and spring to encourage root growth on newly collected specimens. I also put newly collected specimens into a mist house for a few weeks to help the roots get established.

I have read all kinds of information about the temperatures that various species of tree roots will withstand in the winter. According to most of what I've read tree roots should be kept above 20 F at all times. But when I see a ponderosa growing in a two inch deep pocket of soil on bare rock, where winter temperatures can sometimes reach -40 below, I have to assume that they can take a bit of cold.
Ponderosas adapt to life in a pot well, and are generally disease free. The most common pests I have encountered are needle scale insects, which I remove by hand. In the wild the tree is occasionally attacked by several notable diseases and pests including mountain pine beetle, ips beetle, turpentine beetle, sawfly larvae, western gall rust and dwarf mistletoe. All of these except western gall rust can be fairly easily controlled in a potted tree. I avoid diseased trees when collecting to minimize problems later on.
Well, that's my pitch (okay, pun intended) for ponderosa pine, a tree that I think truly captures the spirit of the mountains.