I agree with Vanessa. People can get really hung up on who should pay for stuff like this, but if you have a good relationship with your neighbor and don't want to ruin it, then bite the bullet and have the trees trimmed. He's given you his blessing, plus it is your right to do so. Yes, it would be the neighborly thing to do, but he's not interested in your side of the yard. I live in a mature neighborhood with many large maples, pines, oaks, etc. I like my neighbors, too, but very few people trim their trees. I won't spoil the relationship over something like that. That seems to be the biggest bone of contention amongst neighbors and it won't change. So every 4 or 5 years my husband and I hire out a service to have the trees trimmed and we're very happy. Yes, I'd like financial help from them, but it won't happen and it isn't worth getting upset about. If having the trees trimmed will greatly improve the enjoyment of your yard, then do it. (And make sure you have them trimmed as much as you can because it does get pricey and a tree doesn't stop growing. If your neighbor doesn't care, maybe he'll let you trim the branches totally back to the trunk.) If we didn't take care of this ourselves we'd be living in the Black Forest. And you never know, you might encourage him to do the same thing. Our neighbors really like the way the trees look now and are going to hire their own company to take care of the overgrown mess in their yard because the wife can't grow anything! Yahoo!

You need to look at the mature size. One source says Otto Luyken gets 6 to 8 feet wide. So that is 3-4 feet per side and you have the side of one plant facing the side of another. So ideally that would be about 6 feet apart (or 6 feet "on center" so that the planting holes are 6 feet apart). I just checked Monrovia's site and they say only 6 feet wide. P. S. Buck Jones nursery catalog says they have these in 3 gal, 5 gal and 7 gal sizes. Here is a link that might be useful: monrovia

Wow, I guess I better check my local laws. The concept that city government or a disgruntled neighbor can stop you from taking down or trimming trees on your own property is unbelievable to me. That's all we need, tree police. "Sir, did anyone tell you that certain varieties of holly sustain rare insect life and that by trimming that holly at the wrong time of year, you might have caused destruction of a colony of the super special and rare AB12 variety of Hungarian beetle? This beetle is a food source for the local box turtle population so in effect, you've now put at risk the ability for the mature turtles to feed their young. Yada, yada, yada." Give me a break. "But Officer Evergreen, the holly was rubbing against my siding and causing damage to my house." "Sorry Sir, that's no excuse and that'll be $1500.00." Don't anyone report this SF guy to Al Gore. Next thing you know, the type of pruning he had done will be the reason for global warming.

Many trees gdow from suckers. It looks like the sucker is clear of the rotting trunk so I think you will be fine. Cottonwood grows from cuttings also btw. As far as the lean, if it is leaning towards the sun it may really want to grow that way. Either way with a potentially huge tree like Cottonwood I would try to prune it reasonably straight.