Hi, it's staying tooo wet! The soil these things usually come in is crappy mucky stuff full of peat that holds water forever. You need to transplant into 2/3 small aquarium gravel and 1/3 coarse loam from a garden ctre. And keep it in the sun, but prop a white tile or something against the pot to keep the roots from cooking. Never water to a schedule. Do it when it's needed and finding out when that is for every tree is hard, but if yours is in a faster draining mix, and you water too often, it's less likely to expire from rot - and don't sit the pot in the drain water either (same problem). Forget the toothpicks and use your finger and or just let more of it dry before watering again (don't be afraid to wait X days in between times - it's better than overdoing it, and they need less in winter anyhow. Good luck.

It is very possible that Lucy has hit the nail on the head though I disagree with her soil mix in that she recommends "coarse loam" from the garden center. This is something that is a major problem in that the definition of loam is vague from area to area and any product sold in a garden center is more likely to be as bad as what your tree is already planted in with the exception of the aquarium gravel.

However; this may not be the whole story. Junipers, even though they are evergreens, are not without a cycle of shedding old needles. Usually this happens as the wood becomes lignified and develops bark. Where once green needles adhered, bark starts to appear and the once green needles trunk yellow then turn loose. This normally happens in the interior portions of the tree. The nearer the trunk the more the old needles tend to sluff off. The tree will need transplanting at some point sooner rather than latter but I suggest you do some research on suitable bonsai soil mixes and the methods and techniques of repotting.
Vance Wood.

Vance makes an excellent point regarding terminology. When I first began attempting bonsai there was no such thing as the internet and my reference material was also limited. The books that I owned then said that bonsai were grown in loam. Well to me loam was topsoil, so that is what I used, with less than stellar results. I later found that to the Japanese loam is, at least in the context of bonsai, something entirely different.

Norm

Here is my formula for a decent conifer mix. It is made of three elements.

1.) Sand; # 2 or #3 swimming pool filter sand, also sold as sand blasting sand, but no finer than #2.

2.) Filler: Turface, Red Lava Stone the small stuff 1/4 inch or smaller, Haydite, Scotts ceramic soil conditioner, if desperate the following can be used but not recommended: Hartz Mountain Kitty Litter, or Oil dry.

3.) Organics: Composted Pine Bark Mulch, sold as composted garden mulch, or composted soil conditioner. Do not use Peat Moss it is too fine and when it dries out it is virtually water repellent.

These are the tree basic groups of a soil mix as far as I am concerned. The number two group has a list of possible elements that can be used alone or in any combination of all of them if you wish, but still what ever you put together from this group will be measured as one, be it a cup or a gallon.

The basic mix is one measure by volume not weight of each of the groups, one cup group one, one cup group two, and one cup group three. Sometimes I will add an amount of charcoal especially when dealing with Junipers.

This basic mix can be amended for Maples and other deciduous trees by doubling the organics, group three. Azaleas need to have the organics doubled again.