i have seen them.. as big as a two story house ...

once established ... it is not a shy plant ...

if you cut it at height... expect it to fall over in a year or two... as it puts 4 or 5 new stems.. just as vigorous at the height you cut it ...

google: renovation pruning of flowering shrubs.. to learn how to keep it SOMEWHAT in check ...

i would have never sited it in front of the window.. unless you simply dont want to see past it ....

cut it off 3 to 6 inches from the ground.. and wait for the next one...

ken

I had the same problem with one of my newly planted (as in last spring) Forsythias last year.

ONE single branch over last spring and summer, grew 3 feet taller than the rest of the branches. It looked ridiculous. I was actually a little embarrassed about it, because it's right smack in the front yard, but I left it alone, and this year, in just 4 months of growing, ALL, as in every single one of the other branches, have all caught up with it. I can't even believe the change in this bush. I had no idea Forsythias grew this fast or filled out so thickly, so quickly.

This bush is now 5 feet tall, at least, and so full and heavily branched and leafed that I can't even see where to stick the hose to water it. I am going by how great it looks that it is indeed getting enough water. lol

My advice, going by my own personal experience, is to leave it alone, and that the other branches will catch up.

Edited to add: We put one of our Forsythias in front of our front bay window. It's not right up against the house, but it is in front of the window nonetheless. We did that because we live on a lake and our house is not far off the road at all. You wouldn't believe the number of people who, when they walk past our house to walk to the lake, look right in our front window, sometimes the entire time they are walking by. :Looking at the bush now, I suspect by next year nobody will be able to see in our living room.

This post was edited by ilovemytrees on Wed, Jul 10, 13 at 1:12

If you prune it after it has leafed out it will not respond as vigorously as if you prune it in dormancy. If it is a straight C. coggygria cultivar it will be aggressive but nowhere near as aggressive as Cotinus 'Grace', that has C. obovatus as a parent. C. obovatus is a TREE and 'Grace' is capable of putting on 15' a year. These are shrubs that need to be given enough room. Even the coggygrias can be pruned as small trees (I was just at a wholesale nursery today that had an entire row of standards in 24" boxes), so don't try to shoehorn it in someplace where you have to be cutting it back three times a season.

Having said that, they have lovely foliage, especially in autumn, and the flowers aren't bad, either!

Sara

Yes, they do want to be trees. Some grow them as shrubs and some as trees, and most people never prune them.Then they grow vertically with leggy looking branches. I always prune mine and shape it loosely in the spring before it leafs out so it doesn't have a dozen stems like the one in your photo. So just cut that one back to where it looks consistent with the others.

We have two, and one was infested with borers two years ago. It never dropped its leaves in winter, but dropped them in spring and wasn't leafing out. We figured it was a goner, but I procrastinated having it removed and one day I noticed new growth all over it. Score one for the procrastinator! It's gorgeous now, but the only issue I have with it -- as well as another one in our backyard -- is that they don't "smoke". They bloom beautifully but the spent blooms don't go smoky, which is a disappointment. We had them in Chicago, too, and they always smoked, but not here in KC.

Thanks for the suggestions everyone.

@ilovemytrees, we have the same problem with passers by looking in our front window so we might just let it grow tall. Thanks for posting that...

If you are looking to block the view this might not be the right plant.

If that isn't the plan then I guess you could keep it there. I would prune it back to encourage back budding and more branching. Otherwise that branch will become bare except for the top and may not be able to support itself.

I just pruned back my Grace the other week. You can see it has multiple stems budding out. The nice thing with doing it now is that it won't be as vigorous. Another added bonus is the purple foliage against the aged blue green foliage.

Basically I end up with a 6' plant late June, prune it back early July and then end up with a well branched, compact 6' plant at the end of the year.

You don't have to do this its just what I do as I can't dedicate the space it may need nor do I want lanky growth.

{{gwi:268524}}