White fungus

Hi. I dont have a picture yet, so Ill just write a small text about it. I have seen that on every tree I have, there appears to be some kind of white fungus on the edges of the pots and on the trunk. It comes from the soil.. I have taken it away several times, but it comes back in a just 2 days or so. Do you think it could be a problem? The only problem I have seen is that it doesnt look good. My Ulmus is badly hit by it. The Ulmus is standing in just sand with a small amount of flower soil in it. (Not much). I have it standing mostly in the window sill. I was thinking it was something in the sand, or because of the heat. But now I might fear it can come from some root rot in the pot? Any suggestions are deeply appriciated.
And another small sidequestion. My Ulmus was losing leaves since I bought it, so I got it at a discount. It still is and I have had it for several months. It wont grow and the new leaves are coming really slowly.. I have tried my best to follow advice from pages that explain how to take care of them, but It doesnt help... Its in full sun, inside, and moist most of the time..

Thanks.
-Storm

This white "fungus" . . . is it a thin, dry crust, or is it a thicker, soft, white-bread-like growth on the soil?

If a thin dry crust it may just be a precipitate from very hard water. If soft and white, it may indicate you are watering too much.

Pictures will help.

The elm may also be suffering from a root problem.

How and how often do you water?

Its quite thin and dry at the trunk, and soft and mushy at the soil/edge of the pot. I water about 2 times a week. It holds good on the water and I only water it when its not so moist anymore. Some times 3 times a week if its hot.. Ill try to ad a pic in a few days..
When I water it I put it in a "bath" so the pot has water to the middle of the side. It stands in there untill the top of the soil is wet. Might it be because I use too much fertilizers?

I think it is salt buildup on the trunk and on the soil (and pot???) caused by watering your trees by submersion.

Ah, thanks. A bit better to hear than worrying about rotten roots, hehe. Was considering taking the trees out to check..