I bought three large 60 cm pitch pine saplings and I want to air payer them to make a lot of smaller trees as a shohin material, but is early spring a good time to do it or I should wait and do it when the trees are growing. And also should I use the wire or the ring method? I have read that JBPs can be layered by the ring method. I did two branches today and I used the ring method, but I didn't strip whole ring of bark, just 2/3.
Adventitious root formation depends upon blocking the Polar Auxin Transport chain so that cambium cells get upregulated to being root tips. In my experience anytime a girdle is bridged, the bridge transports enough auxin to preclude adventitious root formation. There are exceptions, of course, but none are pines, AFAIK. IOW, I think you need to remove the entire ring of bark to have a hope. Furthermore, when you do, leave it exposed to the open air for a day or so to assure that any remnant cambium is desiccated (dead) before bundling it up in a rooting medium.
Pines that root are slow to do so. Unfortunately, the older the wood, the less likely it is. I have successfully layered p. thunbegrii, but met total failure with p. mugo and p. sylvestris and p. densiflora. I do enjoy just finding things out, so it will be interesting to know how your attempts with p. rigida work out. On the other hand, pine seedlings tend to thicken pretty rapidly. So much so that I prefer to just grow 0-3 year seedlings instead of trying to air layer older stock. It is so easy to create interesting trunks in small seedlings instead. So, I think
@penumbra is pretty much correct
I don't believe it will air layer. I don't believe pines do in general.
for all practical intents. Regardless, carry through with what you've started.
Also, How important the rooting hormone is? I only have one random nameless rooting powder, no brand stuff.
Rooting hormone will only give the process a kick start. With cuttings it is a race against time because photosynthesis is pretty much a necessity for generating roots. An air layer is still connected to its water and mineral supply, so it won't desiccate in the process = rooting hormone is of negligible benefit.