I want to encourage you to continue your bonsai journey. Glad that Ponderosa pines capture your imagination. What I'm going to type next may seem discouraging, but that is not my intention. You have a nice enough young pondersa pine, continue to work with it. At 18 years of age it is beginning to develop some character, but it needs another 20 or more years to get classic ponderosa pine bark and character.
Ponderosa pine are not particularly good for bonsai, it needles are far too long. It tends to have coarse branches with little or no ramification. They can be tricky to keep healthy in humid climates. There are better species for bonsai.
They are very popular in North America because we can get yamadori trunks, between 100 and 200 years old for modest prices in good quantity. A 100+ year old trunk causes even the most discerning critical bonsai art critic to forget about coarse branches and excessively long needles. Young Ponderosa pines won't show well until they have significant age, at least 75+ years. In the future, if one were selecting nursery stock from seed, I would choose North American species that have better bonsai traits, that will show better at a younger age.
in the future look for
Pinus rigida - pitch pine, it is more cold hardy than JBP, it back buds easily even on very old wood. A reddish brown to black plated bark. It's needles are about same length as JBP, though needles won't reduce quite as short as JBP. Only fault is needles naturally have a twist. It is a double flush pine, like JBP, with 2 or more flushes of candles a year. Trees from seed develop character as quickly as JBP. A good NA species to work with. Probably the best North American species to work with from seed.
These next couple species are good if you can find nursery material from seed or well done grafted cultivars. Some of the dwarf cultivars are really excellent if they have a reasonable growth rate. Most of these can be quite nice in less than 30 years.
Pinus contorta contorta, the shore pines
Pinus contorta latifolia, the lodge pole pine, more cold tolerance than shore pines.
Pinus flexilis, limber pine, a slightly longer needle, more robust growth pattern version of 5 needle pine.
For extreme cold hardieness, consider Pinus banksiana, the jack pine. Some excellent dwarf cultivars available, I have 'Chippewa' and 'Manoment'. Both grow well with very short needles.
there are more, but these come to mind as being better for bonsai from nursery material than ponderosa pine.
worse for bonsai than pondersa is Pinus strobus, eastern white pine. Don't bother, they will be an eternal source of frustration.
. Bark looks more than 18 years. Best suggestion is take to workshop with someone having or working Ponderosa. Please add location to profile for best help.
