The length of time it takes an old stump to rot really depends a great deal on the type of tree. For example, a cottonwood is relatively quick to decompose, but an osage orange may take decades. The best answer is to have the old stump ground out and for the old wood chips from the process removed, filling the hole with topsoil. This prevents any old remaining wood chips from using up available nitrogen as they decompose. Also, realize that this topsoil fill will settle over time and any new tree's root flare will tend to settle down too deeply if not planted very high. Tamping as the hole is backfilled helps but take it from me, if your hole has had any loose soil in it, even tamped, it will still tend to settle and sink the new tree's root flare. If possible, move over four or five feet and plant the new tree in undisturbed soil.
hortster

Not only does it depend on what type of tree, as hortster says, but where you are. Here in western Washington State, trees rot out relatively fast because of the rain. I imagine in west Texas the same tree tree would take years longer. You don't say what zone, or in what location you live, so that limits valid answers.
You can cut the stump off low, and if you can find a spot next to the stump to dig a hole, go ahead and plant. The roots will find a way to grow.
I cut off a stump as low as I could and started a small compost pile above it. Added fertilizer to it to speed up the decomposition, and the stump went away relatively fast.
I kept the compost pile and stump damp.

Filling with the same soil as is around the hole is what should be done. You do not want pockets or zones of differing textures inside the rooting area of a newly planted specimen. It can have adverse effects on movement of water into and out of the rooting area.

Botann, I am in zone 6B, in southeast PA, around Philly. I just added that info to my user name.

Stumps still rotting are detrimental to many newly-planted woody ornamentals. Not knowing what kind of tree was removed it is almost impossible to make recommendations.

Dan

Dan,

I don't have any information on what kind of tree it was. I don't even know when it was removed. The stump came with the yard which came with the house that we bought and all I know is we bought the house two years ago.

Dan, are the new trees silverneedle should avoid generally low or high PH trees?

I'm not very experienced in this soil science stuff but can't see a bunch of swampland bald cypresses, red maples, or black gum (Nyssa sylvatica) caring if there is a rotting trunk near by. Do poor soil loving trees care more?

yep, my worry too - honey fungus is a dreadful problem which might not manifest for some time but there is no cure apart from removal of massive amounts of soil. Some trees/plants must be either more problematic or more susceptible because I come across old stumps in gardens all the time. I do know that people manage their gardens with armilleria present but is is a big risk. Does anyone know whether pyracantha/firethorn is particularly susceptible to HF?

The ID'ing of the tree gives us an idea of how long it will take to rot. If we don't know that, then caution is warranted as the rotting/decomposing fungi may not discriminate between living and dead in their search for usable compounds to complete their life cycle.

Do some exploratory digging and if there are white mycelia still on the scaffold roots, you must wait or dig it out. Or risk mortality on new plantings.

Dan

When you look into the topic long enough you end up with very few kinds of plants being reliably able to fend off a serious Armillaria attack. I think probably the most common variable is whether or not it happens to be present on a planting site.

Another key point it that it does not invariably infest and destroy live tissue. A shrub may grow for decades and then be killed. The fungus was either not present around it up to that point or it was present for some time but did not become aggressive towards that particular specimen until later.

One thing said about honey fungus (oak root fungus) that may be consistent is that it needs moist soil. Here, where we have marked annual summer drought starting in July, older plantings of tough Hardy Hybrid rhododendrons able to tolerate this climate phenomenon (when established) often display dried up, apparently dead Armillaria rhizomorphs on their lower stems. It is as if they were attacked at some point, perhaps a long time ago but were able to survive it. I wonder what role the drying of the stems and uppermost soil in non-irrigated plantings here (summer watering is very often neglected in these parts, where "it rains all the time") might have in this.

Altho honey fungus is yummy and I try never to pass up an opportunity to pick it when I see it, so there are benefits to having it in the landscape. Much less common here than when I lived in WA and CA, however.

Dan

I have an update, and more info -- I was able to speak to the previous owner of the house last weekend and he said that the stump was a sugar maple, and it has been in the ground for at least five years.

What are your verdicts?

Interesting topic, in that just today, we've been told that our 'Autumn Blaze' Maple probably caught a fungus from our old Deodar(dor?) Cedar. About three weeks ago after a very strong wind followed by a couple of 80-85 degree days, the newly forming buds turned to dust. Our gardner was told by the nursery that sold the tree that it was probably had a fungus from being planted ontop of old tree.

The soil is clay, landscaper amended soil, used 'Gro Power' and in the 2 yrs it's been in the ground the area has sunk and it's been a pretty wet winter for So. Calif. Maple is planted surrounded by Marathon II lawn and lawn comes right up to trunk. The trunk/bark has some 'cracks' in it and looks brown around the crack but another area shows green. Also, when the gardner dug up some lawn and soil it does look as if the trunk below ground leveal has some sort of fungus.

Any idea's out here in cyber help?