"Native sandy soil" in in situ situations is a whole lot different than the same soil in containers. There is a substantial difference in how water behaves in containers vs in the garden/beds ....

It's likely you're dealing with the negative consequences of 'perched water' and a lack of aeration, though there is no way to be certain from here.

The link below may help you understand soil air/water relationships a little better.

Al

Here is a link that might be useful: More about soils here

Thanks, Al, for the info. on soils. I moved the juniper underneath our house overhang to minimize rain interception, but am still a bit worried about it getting too wet this winter. There is a much drier spot underneath our front door entry, but the light conditions may not be so ideal, as the roof shades quite a bit (not that there is much, if any, direct sun in the winter here).

Regarding soils: should I repot now, given the native soil may not drain well enough to avoid ponding? If so, do you have any suggestions on preferred soil mixtures? Thanks so much for your help!

Just as a bit more background: I am working on thickening up the juniper stem in the 1 gal container before moving to a ceramic bonsai pot and shaping. I most likely will do this next Spring or Fall, assuming this is good logic...?

I would bury or partially bury the pot in an area that drains well & gets full sun. As far as hydrology is concerned, this turns your container into a small raised bed, so the water/soil relationship is much more like growing in situ. This arrangement takes advantage of the wicking action of the earth. Alternately, you could simply employ a wick in the pot to help you drain excess water. The wick 'fools' the excess water into 'thinking' the pot is deeper than it really is. The water moves down the wick, 'looking' for the bottom of the pot, and gets pushed off the end of the wick by more water moving downward behind it.

Al

Wow, March already! So my western juniper did pretty well over the wet oregonian winter (as did my hemlock). I buried the 1 gal containers in the backyard. Now I am wondering what I should do next to prepare them for bonsai potting and shaping? When is the best time to remove them from the ground, re-pot in ceramic pots, trim roots, shape, etc.? Thanks again!