I would just plant them as soon as the soil is warmed to about 12C directly where you want them (not in water). The roots formed in water often don't do well when planted in soil. The roots usually form at/near lenticels (on the bark) or the callus around the cut, not the cut surface. I happen to love cottonwoods!

We use them extensively around our barns for shade and greenery. We have 'cottonless' varieties, which don't cause the debris or seedlings. They do, however, sucker all along the surface roots, so just be aware that there will be maintenance keeping these chopped out. They are great shimmering in the breeze - the lowlander's aspen!
Sara

Silicaceae, How deep would you plant them? About 12 inches?
Ground is still frozen here. Maybe will plant at the end of the month.

John

I did a two of them several years ago. Stuck them both in 5 gallon pots of wet dirt and watered them along with my other pots. One of them developed roots and grew the other did not.
They were about 18" tall and were "suckers". Pushed them all the way in to bottom of pot, about 7-8" deep. Good luck.
Believe the root came from the bark, but don't really remember that part.

Roots develop from callus tissue along the bottom/damaged part of the cutting and sometimes from adventitious buds along the side of the cutting. In both cases, the growth is initiated from the cambium layer. Sometimes, cuttings are purposely "damaged" (slit, crushed, whittled upon, etc) to provide more surface area to develop callus.

For most woody plants, I like to take cuttings of about 8" to 1' long. I bury at least 2/3 of the cutting, usually leaving 1 or 2 buds exposed.

My sister buried a large limb that blew off her big tree out front. The limb was two feet in diameter or bigger. Everyone laughed, but it grew and grew into another large cottonwood like the one out front in a very short period of time. Unreal!

Sweetannie,

Over two feet in diameter!? What did she use to plant such a monstrous limb?

That would sure be one giant truncheon! And, a tree started that way would have a serious case of butt rot from almost the very beginning.

Unreal!

Many plants that grow along streams do this. It is a survival adaptation.