Having spent many many hours researching the subject of Pine trees, from Autumn through Winter, I have come to ‘a’ conclusion that freezing conditions alone are not the dreaded enemy for White Pine et al.
Scots yes, they will stand a tad more wet in the rootball, than say a Black or White Pine. For the sake of accuracy I am making reference to White as grafted material to Thunbergii (Black) root stock, and not White on own roots per se.
Having discussed the matter of recent winter conditions with experts in Bonsai, and in particular, a research professor with a well known University, I have concluded that one alone is not sufficient to cause the loss of this species (grown as bonsai) as has been sadly experienced up and down the land during 2008-2011.
I therefore am of the opinion that to keep these species as safe as possible, going into freezing conditions on the dry side is of the utmost importance. Oh yee of little faith! I can hear the sighing already. Pretty darned obvious if you think about it; yes, I agree, but not always possible with a larger Bonsai to pop it under cover. Do you heat or not? To some degree yes; this is about managing your trees. Not an easy one though as it is crucial not to overheat. For example; if we experience silly minus figures, then look to achieve an increase to just freezing. Bring it up to zero say from -10c and lower, but not to go into silly + figures.
If you must heat, then look to bring it up to say +1 or 2c (at the most) but try to do this during daylight when a Pine is at its most active. Heating at night with this species achieves very little indeed.
What is a potential killer is soggy wet conditions and severe freezing immediately afterwards. Keeping the root ball towards dry will do no harm whatsoever during the ‘off’ season, unless …. the tree has been subjected to harsh drying winds. Sure, movement is far less than during the growing season; but be warned; these very strong winds during the latter stages of 2011 and into 2012 will dry the tree out very very quickly. Not an easy one if your tree happens to be a heavy and large one. I hear much bantered about ‘popping’ it in the garage or shed. This will work fine as long as it is managed. Ensure light still gets to the pine; do not put it in a dark windowless environment … and don’t forget it either. I stress the need to manage! This is down to you, no-one else.
So, aim to keep it dry (ish), and if needs be use a moisture meter, a good one at that. On a deeper pot whilst the surface may seem dry, elsewhere, further down it could be amply moist. Check all round the rootball with a probe.
If you do nothing else then please just remember … manage-manage-manage the tree. Do not leave it to chance. I have, during a near three decade of this wonderful art, and sadly must say I was a fool!
On a nicer note although chilly today, the sun actually came out for a change. This winter sun will assist a JWP in particular, in keeping a grand colour.