Instead of Europe you might as well say East Coast.
Growing Ponderosa in Europe
by Walter Pall
When I first got in touch with Ponderosa Pines in America I listened to all sorts of advice of how to take care of them. The advice I got in a nutshell: water sparingly, do not expose to rain in winter, keep very dry, feed very little, almost no nitrogene as it will cause very long needles. In more than ten years of caring intensively for more than a handful of Ponderosa Pines in my garden in Germany I can say that obviously the opposite of the general advice works much better. I can say this comparing the looks and vigor of my trees with just about all Ponderosa Pines that I see in America on my many trips. I have seen too many trees which were not in good shape at all and obviously going downhill. Most Americans coming to my garden could not believe that what they say were Ponderosa pines. They mistake them for black pines normally. So it cannot all be wrong what I am doing.
What do I do?
Water: It is correct that the Ponderosa Pine is able to survive long periods of draught, but it clearly grows much better with normal watering which compares to other pines. A prerequisite is a very well draining substrate. Then one can and even should water every day heftily. If the right soil mixture is used one can leave the pines in one location all year round, also during long rainy periods. It sometimes rains for ten days in a row where I live and the ponderosas afterwards look healthier than ever.
The chemical contents of the water don’t seem to matter. If water with a high concentration of calcium is used over extended periods of time it does not do harm to the trees but a grey film on the needles may well be the result.
Long needles are the result of a combination of much water and feeding as advised here. Therefore a ‘finished’ bonsai will finally get less water and feed. But this only after more than a decade in development.
Repotting: Collected trees can stay in the same substrate for a very long time. But this is only true if they stand in modern bonsai substrate! The soil from the natural habitat must be removed as soon as possible. Coming to think of it the main difference between my ponderosas and the ones that I see in America is that mine had to be bare rooted at import and that the American ones usually stand in the soil of their habitat surrounded by modern substrate. Afterthis original soil is removed it often is not necessary to repot for more than five years. The best time is spring. When repotting one should use the chance to remove old soil from the root ball which still might be there. Collected trees should not be root pruned for a long time. The roots should be left in the full length as the tree was collected. If necessary they can be somehow crammed in a spiral form into the container. Collected trees often have a very firm root ball which has awkward shapes. It has the shape of the pocket in the rock where the tree used to grow. Sometimes it is difficult to plant this root ball into a decent bonsai pot. The ancient roots cannot be bent without severe damage. Therefore the bonsai enthusiast is advised to first of all try to find out into what sort of container the tree will fit at all before the crown is styled. It does not make sense to style a good crown over many years, only to find out that the pine never will fit into the forseen kind of container.
Soil: The substrate must be very well draining and aeriating. It should be slightly acid to neutral, sandy with no or almost no organic content. Andy Smith recommends 70% coarse Akadama or similar plus 30 % bark mulch. Other bonsai enthusiasts work with granite gravel with added organic contents. Very good results were achieved in Central Europe with a mixture of 85% coarse pumice or lava or baked loam plus 15% rough peat. With all these substrates it is quite important to know that they contain almost no feed. It is therefore indispensable to feed a lot and often.
Cutting and pinching: As with all pines one must never cut back a branch to where no or very few needles are left. The branch will die inevitably. One can expect that a Ponderosa Pine will develop several buds on the tips, but they hardly ever bud back into old wood. Therefore one should avoid cutting off branches as far as possible and rather work with what is there and create a good crown with the existing needle whirls.
For getting shorter needles one can also practice the following method: In May with all whirls the needles are cut back to the length that one would have liked. The buds must remain intact. These buds will develop candles which have a bit shorter needles, because they get somewhat less energy from the shortened needles. The tips of the needles will look slightly ugly though for one season.
In late summer the buds for next year appear. With Ponderosa Pines these are very often the rhombical flower buds all over the tree. Flowers should be avoided. In fall the rhombs are rubbed off in such a way that the very center, which is the normal needle bud stays. On very healthy trees one can also take off the whole flower bud.
Feeding: Regular feeding throughout the vegetation period is a must. Good results are achieved with organic as well as anorganic feeds with medium to high nitrogen content. Strong feeding in fall stimulates the development of buds, even several buds on one whirl. In spring and summer slightly less feeding is appropriate to avoid too long needles. But during development of a bonsai one can well work with very high nitrogen contents in organic feed. Long needles will create a lot of energy which leads to lots of backbudding. Later, when the bonsai is ‘finished’ one can feed less.
Location: Ponderosa Pines want a lot of sunshine. A location in full sun is just right. Even in very hot and sunny summers they grow very well as long as they are watered well. In summer at temperatures of above 30°C partial half shade is required when one cannot water fully every day. When substrate is used that is not very well draining it is important to protect the tree from long rain periods. In most areas a location on a wall facing to southeast is good. The rain, which usually comes from the west will be kept away by the wall. If the recommended kind of soil mixture is used it is possible to leave the Ponderosa Pine at the spot even in long rainy periods.
Hardiness: The pine is hardy to very hardy (zone 5b). It is jeopardized by late frosts. Recently collected trees need good protection for several years before they are fully established. In winter they should be protected from permanent rain. On the other hand it is a big mistake to keep them too dry in winter.
Diseases: The Ponderosa Pine is usually free of diseases and critters as bonsai. Sometimes one finds aphids which can be removed with the fingers. One can spray with oil emulsion in late winter as preventive measure. Collected pines with much deadwood can contain bores which can become quite dangerous. Small mistle toes in the branches are not cute but reason for immediate alarm. They will kill the tree and there is no cure.