Wood filler for deadwood holes?

I have a general question about wood filler.

Some deadwood on a Utah Juniper I have is rotten, so I'm going to clean it all out. However, because of the shape of the deadwood, there's no way to remove the rotten wood without leaving a hole that is going to pool water. So, I need to fill that hole somehow. I was thinking that maybe wood filler/putty might work, but then I heard there might be expansion problems, whereby the trunk and the filler might expand and contract at different rates, potentially leading to problems.

So, does anyone have any advice about filler? Is there a good brand? Is there some other technique I could use?

I was even thinking that using some silly putty might do the trick better than anything else.

Concrete works.

Interesting. I'll look into that, but I think it might be too much. The hole is no more than half an inch in size (the tree is only 12 inches), so the work might not be worth it.

I think wood filler could work. We made our own in shop class out of wood glue and sawdust.

That's clever. I could even use the sawdust from the hole I hollow out. That just might work.

not sure if this is a good suggestion or not without a picture, but drilling a small drainage hole may alleviate the pooling...

That might work in other situations, but the hole lies at the soil level, more or less, so there's nowhere to drain too. Good idea though.

External wood filler is designed to expand and contract at the same rate as the wood it is attached to so it should work. Most of my trees with holes that look like water will pool in them actually drain into the tree within a few minutes of watering but that may not always be the case of course.

John T - MKBonsai