Been a lurker here for several months - love seeing what you're planting, Jack. I'm from central CA and miss it terribly - now in southwestern CO - high desert and still in major drought. I do have irrigation water, but it may be curtailed this summer if we don't get more mountain snow. I love seeing those cottonwood seedlings - am going to try some. I have two huge very old trees, right on the irrigation ditch, and they are way overdue to fall, so will try to propagate some new ones, though I'll never see them mature. Did you use a rooting hormone for them?
