Advice from Colin Lewis.
You don't need to worry about needle reduction until the branch structure
> is
> complete and you have a reasonable number of buds and shoots.
>
> Ponderosas are the opposite of black pine - needle reduction is the result
> of deprivation and density rather than vigor.
>
> Deprivation-1:
> Water normally in spring until the needles are about one and a quarter
> inch
> long, whereupon reduce watering to an absolute minimum, probably less than
> you feel comfortable with. If you water other trees every day, water the
> ponderosa every three days, etc. (Modify this regime to account for soil
> type and age.) Do not resume normal watering until the needles are dark
> green and fully hardened, probably not until mid to late August, maybe
> even
> early September - you'll need to use your judgement there.
>
> Deprivation-2:
> In spring do NOT feed nitrogen. Use 0-10-10 or a combination of
> superphosphate and potash. Only include nitrogen in a balanced feed once
> the needles have become dark green and fully hardened. This influx of
> nitrogenous energy will go into bud production rather than needle and
> shoot
> growth.
>
> Deprivation-3:
> Repot very INfrequently. Most bonsai are repotted too often anyway, but
> once every seven to ten years should do for ponderosas. The slow-down in
> root growth is reflected in slower and more compact crown growth. The
> longer the tree has to tolerate an inhospitable root environment, the
> smaller will be the buds and the shorter will be the needles.
>
> Density
> The theory goes that any given root mass has the ability to support a
> given
> maximum surface area of foliage. When roots are confined in a pot
> (especially for a long time) the tree eventually develops the maximum
> number
> of buds that it can support with full-size needles. The following year,
> with even more buds, the tree has to choose between sacrificing some buds
> or
> reducing the size of the emerging foliage. Provided the tree is healthy
> it
> will chose the latter. This principle applies to almost all species,
> coniferous, deciduous or tropical.
Harry, Don't remove buds from ponderosas! Unlike black pine, they're not
strong enough to regenerate over winter. You can cut NEW candles back to
three or four pairs of needles in spring, or remove them completely of they
are very vigorous, but in fall, no.
Last year's needles can and should be thinned. You'll find that if you try
to pull them the bark will tear. Ponderosa needles need to be cut off with
sharp scissors, just above the fascicle (the papery sheath at the base.
This preserves the meristematic tissue at the base of the needles where new
buds form. By next spring the remains of the needles will dry out and fall
away.
Colin
Here's the one I bought from Colin,
Harry