Not seeing it ...it's hard to know... but if it's the main branch you may ultimatly screw yourself by having a weakened main stem that will break at a later date when it's really nice. If it were mine I'd cut below the split and live with it ... most JM's are fast growers and next season should look fine... but if you have it go kaput as an older tree it might take years to look "good" again..Jm's enjoy trimming anyway and now is a good time to do it...take the plunge you'll be glad you did IMHO ...of course not seeing it I am basing this on your rather sparse description ...David

David thanks.
You bring up a very good point. I did some research on google and it seems that plants do not actually heal like we do, they just build tissue to cover cuts etc. and the integrity of a split branch is always compromised.
So I guess now is probably a good time to cut it below the split rather than later.

thanks

yes the sooner the better... I learned from another that late winter and spring unlike most other trees and bushes is an especially bad time to prune JM's since the sap starts running then and can cause more stress to the trees remember it it a maple and it will bleed sap... even in the middle of summer is better than the time most trees are pruned ..David

David,

I read somewhere that early spring is the best time to prune, and some place else that winter is the best. I am confused as to when is the best time. I have another 4 year viridis that has gotten very twiggy that need pruning, but is still in full leaf(not even started the fall colors yet). Should I wait for all the leaves to fall and for it to go dormant before I prune, or should I prune now (hoping to remove 10-20 % of the twiggy branches)?

thanks,
xman

Here is a link that might be useful: Here is a link

The general rule of thumb on most trees is to prune in late winter and early spring .except for blooming bushes ( and I guess blooming trees also ?) which should be trimmed just after blooming or you'll screw up the bloom for next season I pruned one of mine in July and it was fine...BUT maples are trees that the sap rises in late winter and early spring ...so when you prune during that period it makes some sense it will not be the best time since it may stress them ... But most JM's are very hard to screw up once they get established so if you do it in sap rising time I'm sure it would be ok but only if you have no choice ...you do though...BUT I see no reason NOT to wait til the fall color is over and do it then...the sap won't be anywhere near the spring stage...So if I were you I'd wait and enjoy the color then immidiately do the deed ...David