Choose a spot with full sun and a naturally moist soil, dig a typical planting hole and mulch after planting. Even with irrigation it will be a chore to fulfill the moisture requirements of a willow of much size year after year unless the spot is not already suitable on its own.

I'm not sure if you understood my question. If the tree in 2 or 3 inches below the ground at a 5 foot diameter and you fill it with water once a week it's will get lots of water without it running off.

I'm not sure any trees *LIKE* having their trunks surrounded by water, willows just tolerate it better then most. Depending on how well your soil drains, you could still rot the trunk. Also, you don't want mulch to touch the trunk...it can hold moisture against the trunk to long, and provide both food and shelter to bugs.

First, the roots of a weeping willow will extend far beyond a 5' diameter circle in no time at all. And I don't know how long you think that moat of weekly water will last, but in decently draining soil, not long at all. You should probably bump that up to every other day in summer for the first couple of seasons

Honestly, the first response you got summed it all up very well. These trees prefer a consistently moist soil and will typically tolerate a wet soil, which is why you often see them sited immediately adjacent to ponds, lakes, streams and other water courses.

Lostsoul, where are you?

If you are in a climate similar to StLouis I say stick a cutting in the ground, water it for the first year and see what happens. My neighbor has one which I swear he has watered ONCE since its first year in the ground a decade ago. Its HUGE now and planted on a well draining hill with deep soil. Other yard willows I see in old neighborhoods seem to do well. Sometimes new construction yards require a bit of help if the soil was stripped.

If you are stuck to a dry mountain in Colorado or in the dry Phoenix desert I say don't bother.

bill_minn_2b(Z3b WestCentral MN)

I would never plant a woody plant below the natural grade. Why?

You could build a little dyke to keep water from running away . That seems silly because I don't want to be running my lawn mover over a dyke. So what is the difference? The whole idea is to keep the water from running off.

'Why?'

Simply because that's not the way trees grow. The trees root crown is meant to be out of the ground so it can breath. Putting it below grade invites it to stay too wet. Also over time the depression can fill with rotting mulch, leaves and dirt, essentially smothering the plant.

Why would you want to run your lawn mower over the area that you have filled with wood chips? That would seem more silly and would make a mess of things.

And the dyke can be removed after it outlives it purpose. :)

first... weeping willow is a nice park or golf course tree .. most of us would suggest no closer than 50 feet to a structure ... of course you dont say what kind ... so i generalize ...

second .... you dont mention size .... and i am sure.. 5 feet is way over the top... maybe a foot for every inch caliper ...

once extablished.. in a year for a willow .... you should never have to water it again ...

first link is a plnating guide ...

second link is a pictorial on what i call a moat for watering ...

its a good idea for the short period a transplant will need water.. but most likely way over the top ...

ken

guide

https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub

pictorial ... but i cant see the pix... and hoping they will show later ...

http://forums.gardenweb.com/discussions/1827881/how-to-transpalnt-a-conifer-tree-huge-pix-post

see new note at bottom of link above ... ken