That's great information Leo, Thanks so much for writing that out and sharing your experiences. I have two, one I've had for 2 yrs now and one I got this spring. I fed the hell out of them, even in the spring. So yes, I got long needles, but I have back budding and I haven't done any candle trimming yet. I just pruned to more proximal buds on my older this fall for the first time. The second is one of Andy's 'burlap' trees and given that it was just potted up this spring, it grew very well with a fair amount of back budding even! And I haven't done a darn thing to it exc. feed it aggressively. So I've taken a kinda hands off approach to needle reduction, candle trimming etc. so far.
My potting mix is a blend of dry stall pumice, turface, granite grit and some akadama. A small amount (10% or less) of used on the orchids, orchid bark. Since my main collection is orchids, used bark is easy to get, a full year of 'composting' before being repurposed to bonsai mix.
Fertilizers and feeding - Because of the orchids, I have a set up that makes using liquid fertilizer very easy. I don't use a proportioner, because the less than $100 units are prone to inaccuracy & break down. I am able to mix fertilizer directly into the water I'll be using. SO, that said, the bonsai get the same water the orchids do, which means, whether I want to or not, I am using a continuous feedling program. Every time I water by hand I am dosing the trees with a very dilute dose of fertilizer, about 50 to 70 ppm as N. The nutrient ratios were designed for producing bedding plants in synthetic soils, then modified slightly for orchids. Since we are using synthetic soils for bonsai, I am convinced this is a better blend than what is commonly recommended. The ratios are 13-1.8-2 with 8 calcium, 4 magnesium, and a very long list of minors in precise proportions. The color of my pine needles are excellent. My 6 Ponderosas went from yellow green to rich green with a little blue tone in the first season. Unfortunately needle length is a bit on the long side. This is not a heavy dose of fertilizer, I have to add cake fertilizer to my Jap. Black Pines because they clearly are not getting enough, especially in spring. This dose rate does seem near ideal for JWP, but then again all my JWP are youthful trees, still in early development. My longest in my care tree, a pomegranate, seems to really appreciate this, though like JBP I add cake fertilizer in spring after it goes outside.
The first one is in mainly pumice that has broken down over the last 3-4yrs since the initial pot up. Stays wet at the bottom of the pot, but is draining well and growing well. I'm thinking of repotting it, but like you said, if it's draining well, then does it really need to be repotted despite the wet feet? I'm unsure and haven't made up my mind yet.
Having lost 3 trees due to rushing them, my thought is that if a tree is over 100 years old, and has not been in captivity for at least 15 years, then be reluctant to re-pot. 4 or even 6 years between repotting is reasonable, especially if your mix is mostly mineral, without much in the way of organics. These trees are still adapting. If the mix is draining well, the break down of the pumice is likely not a big deal. I've noticed that Akadama will loose its appearance of structure fairly quickly, yet the trees don't seem to mind, grow quite well in fact, at least for another season or two. I do believe repotting is necessary, but I think until one sees very, very vigorous growth, it might be best to take it slow.
For the majority of us, I don't think we have seen truly vigorous ponderosa growth. Most of us are dealing with trees that have been less than 10 years in captivity. Judging by the dense needles on the upper branches of the largest and least 'worked' of my surviving ponderosas, I am guessing when they get truly growing, they will be very vigorous, more like a JBP growing in moist coastal California (not a desert grown JBP). I am thinking the large amount of back buds and nice big terminal buds is only the beginning of the pick up in vigor. I am going to still hold back and see if I can get the dense foxtails of needles even in the lower branches. Then I will work the tree like a tree that is established.
If I had your trees, the growth you describe I would guess is signs of 'half way' on the way to vigorous growth. I would still be slow to do much with them.
Pam W. in the Milwaukee bonsai club has a very nice small Ponderosa that looks more like a JBP with very old bark. She left it alone, without working it much beyond infrequent repotting for 15 years before starting to really work the tree. Part of that was she hadn't decided what
to do with it, initially no design options leaped out at her, except it kept saying 'potential'. I don't think we have to wait that long, but the health of this small tree was remarkable when I saw it at a workshop with Ted Matson we did together. SO my advice that I have to keep repeating to myself to keep myself in check is to GO SLOW at first and that SLOW zone may be 10 years.
Now I don't mean do nothing, but with 3 dead $250+ trees behind me, I am thinking SLOW is good. One work day per year, or one technique per 12 months for a while, for possibly 10 years or so. The reason I say 'per 12 months
' is that I tend to think pruning & needle work in fall and repotting in spring as being a year apart, yet only 5 months may have actually passed.