With the weather currently mild in ‘most’ of the UK, buds are certainly on the move with deciduous varieties of our Bonsai. I therefore felt it was relevant to say just hang on a moment before heading off to the potting shed and getting all the bonsai out of their containers and repotting everything now!
It is quite early in the year to really consider a full-on repotting schedule, and the optimum moment, certainly with deciduous trees is to undertake the repotting as the buds reach maximum swell and just before a leaf starts to appear; I can only speak for my own in the SW of England that are all over-wintered and not a one is anywhere near ready. Some species are not quite so simple to guage such as Larch. Once the new growth is hinting green with tiny little shaving brush type growth evident, then this is the usual time for a repot.
It does seem as if 2011 is going to be generally early for new growth; and this in the main will be down to any over-wintering you have organised in unheated greenhouses and similar, and of course temperatures above 10 degrees C for quite some consecutive days now.
It is vital to wait as long as possible; repotting too early will place even further strain on the Bonsai and it will not have reached anywhere near new growth and sustained health factors. Clearly when we repot it is not just because it amuses us to do so; Repotting must NEVER be carried out just on a whim; you will need to measure species type against when it was last repotted and compare also last seasons health and how it seems now.
Once extending buds are visible is the best time for a repot, be cautious though, this window can be easily missed as bud extension to an unfolding leaf takes place very quickly indeed. I cannot stress enough that when you have repotted, feed just the once, well with a multi-liquid-vitamin/hormone such as Superthrive or Superdrive; the latter basically being a watered down version of ST. Once repotting at the correct time has been undertaken DO NOT just put the tree outside on your display benches/area. It will need a time of protection from harsh weather elements and of course the cold weather which undoubtedly we will see a return to at some stage – before we can safely say we are out of the woods. No more watering until it requires it and NO feeds at all now for at least six further weeks.
As far as those evergreens are concerned later is better than sooner; new growth or developing shoots should be clearly seen and a usual good time as a mean average would be from early March (at the very earliest) to perhaps even mid to late April. Again general protection should be included post repot.
Above all else just keep an eye on the weather forecast for your own area from now onwards.