We have one, so speaking from personal experience only, it being grafted is much smaller than its cousin. The tank being probably concrete should be impervious to the roots unless there are cracks. Even so, 15 ft should not be a problem on this tree. I would not plant anything that will get regular tree size.

i would suspect.. they were talking about the 50 to 100 foot willow..

rather than this little thing.. which i would call a shrub.. long before i would call it a tree ...

the issue would be the access point to your holding tank .... no plants have access to cement drills.. and go thru an otherwise intact sidewall ...

so if your tank top is secure.. then i dont see where a tree will invade it ...

but i would still stay 10 to 15 feet away ...

there are plenty of large perennials.. that could go closer... that lack the root mass.. to be a problem ...

BTW .. willow roots rather freely ... if you were to take six .. 6 to 8 inch cuttings... and stick them in some good media.. and put it in full shade.. no sun ... and keep it damp thru summer.. not sodden.. just damp.. and being willow.. you will probably have 7 footlings by fall ... dont ask me how.. lol ...

just an issue of instant gratification .. as to size ...

ken

Exactly! This is not a tree - it is a shrub willow grafted to another willow rootstock. But even the understock is rather docile compared to larger growing willows and is unlikely to become problematic with septic systems, leach fields, inground plumbing or ponds or pools.

Thank you for feedback. I will plant another one. Beautiful ornamental tree, BTW.

New growth is spectacular. Give it a hard pruning early every spring (March works best around here)