On the old ABS Yahoo forumTom Simonyi asked for people's experience with forsythia. I've worked with a forsythia quite a few years. The leaves don't seem to reduce all that much, but they do to a certian extent if one keeps on top of pinching new shoots. They will develop pretty good ramification as well if new shoots are kept pinched back.
One needs to pinch the new shoots back to one or two leaves as they start to elongate and are still soft. You really need to stay on top of this in the spring after flowering. Forsythia should be repotted every year or every other year. Mine is pushing itself up out of the pot after two years. It produces a ton of roots, so repotting every year isn't a bad idea. They are fairly thirsty, so use a reasonably deep pot and don't fail to water in the hot weather. For soil I recommend either straight lava rock, or 2/3 lava rock and 1/3 akadama, which is what I am using. Repotting can either be done early spring before flowering, or after flowering. I prefer to repot before flowering.
I like to clean up the branches and wire in the middle of winter. At that time of year the new buds are hard and tight and you can clean off old flower debris and wire without damaging them. I always bring mine out right around January first or thereabouts and trim and wire branches as necessary. If you wait until spring the buds start to swell and get soft and you will end up knocking off a lot of flower buds at that time.
Here are some pictures of my forsythia.
I have let the lower right branches grow a little long to thicken them up.
