Gavin and Dan,
Black pine needles go through a 3 year cycle: year1 candles grow and new needles open; year2 needles feed the tree, new candles grow and new needles open; year3 new candles grow and new needles open, last year's needles feed the tree, 2yo needles are becoming old. Mid-late summer they will start to go yellow, then brown then fall off. Usually you can count back years of growth by looking for bare sections of trunk between needles.
Here's a photo from a post on my website
http://shibuibonsai.com.au/shibui-guide-to-pines/ to show this
Pine growth.PNG
Note that the picture was taken in winter (no leaves on the maples behind). In spring there will be an additional growth at the tips when the new spring candles grow and open.
From that you will be able to infer:
1. You can allow black pines to grow for at least 2 years. Needles do not fall until year 3.
2. If you have let it grow for 2 years (or you can't work out how old the growth is) you will need to prune before midsummer because the older needles will be getting ready to drop after that and may not bud readily.
In the picture above you could cut down to where the previous season growth arrow is pointing, just leaving 4 or 5 pairs of needles and expect to see new buds form from those needles (I think the needles on the 3yo section are looking too poorly to bud well). At the same time I would probably also cut all the branches back to leave just a few needles so they will bud back as well.
(In the case pictured that would still leave a long thin tree so, in that case, better to cut much lower and use a side branch to grow a whole new trunk and apex - at last to the 3year ago arrow and probably down to the 2nd small branch on the right side.)
3. In reality you can prune any time of year - as long as you leave some healthy needles- Autumn, winter and early spring pruning will result in strong, large candles which is good if you want the tree to continue to thicken. Late spring/ summer pruning results in smaller candles with needles closer to the base, just as it does when we decandle later.
and do you thin out the shots in summer ?
Not really sure what this is asking Dan but it does remind me that normal pine growth is whorls of branches - look at the photo again. 3, 4 or more branches at each spot if you allow them. You can see that those spots are already starting to enlarge - reverse taper does not look good so cut off extra shoots from any part of the tree you plan to keep - another reason for cutting low down on that tree and because I was planning to cut low there was no need to thin out those whorls
All the possibilities are difficult to write down. far easier to show so try to find someone who can take you through it with a couple of trees as examples.
Also note that there are always several ways to reach the same point so you may get advice which seems to conflict but may still achieve the same result.
