Soon as i read the part about the 'tree' ... not 'plant' staying indoors i stopped reading...

Al

To clarify on the previous post, Japanese maples, Acer palmatum, are NOT houseplants. They will not receive the necessary requirements for good health and proper growth being kept indoors.

Take your plant outside and keep in a somewhat protected environment (out of direct sun/wind for at least part of the day). Pay close attention to watering and fertilization. Once it has lost its leaves in fall, bring indoors into a cool location. Not into the main house with 70F heat........a cool basement or attached unheated garage, etc. The tree wants to become dormant in winter so needs the cold but needs to be protected against freezing weather.

Ggal is correct...i should have explained further. Sorry if i came off rude.
Best of luck!

Al

Gardengal and alley_cat,

I did not try to make a houseplant out of it, but a bonsai. I guess I should've picked the right forum from the beginning! That'll teach me. :)

Thanks a lot anyway! It is outside already.

A maple tree shouldn't spend anytime indoors, bonsai or otherwise.
They need a period of dormancy to grow well. All my bonsai's have never been inside.
Where do you live? What Zone are you in? If you live in a real cold climate in winter you can bring your potted maples inside in a unheated garage to escape winter's coldest weather. The smaller the container, the more important it is.
Check out the Bonsai Forum.
http://forums.gardenweb.com/forums/
Mike

Hmmmm.......if the plant stays indoors, it's a houseplant, bonsai or not. And it really doesn't make any difference what forum you choose to discuss this on, they will all tell you the same thing - bonsai or not, maples CANNOT live indoors.

That's what's the matter with your plant. It is suffering because it is not getting sufficient daylight or sufficient humidity and is provided inadequate temperature variations. And because of the confines of bonsai growth (small pot, little soil, restricted root run) you will need to fertilize frequently, which has not been confirmed.

Mike,

thank you for the suggestions, I have read a lot of discussions on the bonsai forum, very useful indeed.

Gardengal,

sorry, what I meant is - the idea was not to have a maple as such, otherwise it would be outside in a huge pot like our willow.

The plan was to train it into a bonsai, so after we bought it, it was outside until the winter (and did well too - got a nice thick trunk, went from about 9 mm to 15-16 mm and developed lovely foliage). Winters are not cold here in Belgium but very-very-very wet, so after it shed its leaves, somewhere in November we took it inside to prevent its roots from rotting. I guess inside was too warm, even in the unheated room it was put in. So the new leaves appeared way too early and looked unhealthy. It seemed logical in that February to not put out a tree in such bad state, but keep it inside until figuring out what's wrong (I suspected an infection/infestation so I sprayed it with a combined fungicide/acaricide once). Later in the spring I have put it outside for a few days, as mentioned, but it did not improve at all, even got a bit worse from the sun and since then it was inside (a year and a bit, this winter it went also bald and sleeping, but too short I suppose, since the leaves look the same).

I have been trying ever since to find the cause/treat it. Now it's obvious it is the bad dormancy(ies) and not a bug or virus/fungus. Plus keeping it inside probably made it even weaker.

Now it is outside. The pot it is in is not a real bonsai pot, it's big and deep enough, wider than the crown and about 13 cm deep (it does get fertilizer - none in the winter, once in two weeks since the leaves appeared), so I won't stress it with a repotting so late in the year. I'll just leave it outside and improvise something to keep it relatively dry in the winter.

Hopefully next year we'll have a healthier tree and can resume bonsai-ing it in the years to come. :)

"(I suspected an infection/infestation so I sprayed it with a combined fungicide/acaricide once)"

Never, never, never treat any plant for a pest or problem you merely suspect. Identify the pest or problem to a certainty, then investigate treatments or controls.
Always choose the mildest remedy, and even then some plants JM's being one, do not take kindly to being sprayed with anything.

A stressed plant is particularly unable to withstand chemical treatments, especially those not warranted.
Sometimes our best chance at growing a healthy plant is to leave it alone.