Soils that were under spruces can develop very low pH (you mentioned acidity). I have seen soil tests from such soils at 4.3-4.5. I would suggest that you have a soil test done to see where yours is at and if lime might be required, or even if you should pick a different location. Honeylocust does fairly well around here (KS) in our HIGH pH soils. I have seen areas where spruces had been removed remain almost bare for years, leading me to question whether I would try what you are thinking about doing.

The US Forest Service and USDA both state that pH tolerance of Gleditsia triacanthos is 4.8 to 8.0. The "ideal" pH is 6.0-8.0. You also might talk to folks at your local extension service since in CO they have probably had experience with this.

In regard to pH....it is HIGHLY unlikely that you will have acidic soils in Denver, regardless of the presence of a spruce or not.

if you can dig the hole.. the stump is irrelevant ... took you more time to type up the post.. than it would have taken me to plant it ...

if you hit some dead old root.. work smart.. and dig your hole a few inches away from the root ..

the downspout will most likely wash soil away from the tree .. rather than provide water... as it will run right past it ... you will need to divert it.. and figure out how to slow it down ... to soak in, before it runs further down hill .. or better yet.. just water it properly..and dont rely on rain ...

see link for planting instructions...

do you see any other honey locust in town.. thats my usual indication of its tolerance to native soil ... also .... the same.. if purchased locally ... rather than mail ordered in.. most good nurseries.. dont sell things that wont live ... a quick call to your COUNTY extension office will also get you a fast LOCAL answer ... [if buying from a hardware store.. good luck with that]

ken

EDIT: fir typos.. lol .. FOR typos ... crikey ...

Here is a link that might be useful: link

This post was edited by ken_adrian on Wed, Apr 30, 14 at 9:39

Tough tree -- should be fine. Quite drought/heat tolerant once established. It's the only tree that grows non-stop thru the hottest, driest periods on my lot. Mine's 35' ft tall after 10 seasons.

heat and drought tolerance.. has nothing to do you new tree ... prior to a recently planted tree get ESTABLISHED ... which.. depending on size.. could be 2 or three years .. for those 2 or 3 years.. you are responsible for all watering.. and deeply thru the root mass planted ...

the easiest solution to avoid soil erosion.. would be to extend a 4 inch perforated pipe... past the tree ... then some water would shed.. and the remainder carried further on....

do not confuse yourself about how the big old pine coped.. and then make presumptions that the new babe.. will do the same.. immediately ... it will.. but it will take time ..

good luck

ken

Honeylocusts are usually recommended for adverse conditions, but most of the ones around here look like hell. Some bug disfigures the leaves and a lot have dieback.

FWIW, the gutter drainage could be made to benefit the new tree if you can somehow "slow down" the flow of water and maybe trap it.

In my climate, it would probably be too much water, but in yours it might be "just right".

One trick I've seen is to let the downspout hit the top of a large rock, and the water will then run down the sides of the rock, slowing it down enough to at least somewhat soak in.

I doubt the soil pH would be an issue. Your soils there are rather alkaline to start with, so even if acidified by the spruce, it won't be to a level where you'd have any concern.

Folks, we make calls based on our own experiences. Admittedly, I have only seen two soil tests from soils under old, large spruces, and as I said, they were 4.3 and 4.5 pH. The normal pH around here is typically high.

There is a ton of info on this if you google "soil acidification under spruce."

Here is a link that might be useful: Soil acidification