Question
I am in Western New York (Buffalo area)

Can a forsythia bush be safely pruned back beyond where the leaves are showing?  If so, what cautions should be taken, what time of year should it be done and what is the likely length of time needed for the bush to recover, show good growth and regain the appearance of a healthy plant (fully green without showing much branch)?

Answer
Forsythia is kind of like asparagus, in that you prune it back all the way to the ground...you usually take about 1/3rd of the stalks out, starting with the oldest &/or dead branches that have bloomed already.  

Now is the time to prune, after blooming.  It will continue to grow, and send up new shoots, but the "showy" time, with the most new growth/blooms is in the Spring (Feb-April).

You won't kill it by pruning it now, in fact, you'll make it a better bloomer next Spring.  Its a tough plant.

Regards,   Marc