What a great question. I planted a row of forsythia last Spring and have been wondering the same question myself. Can someone chime in? Anyone?

It was a much bigger tangled mess but I severely pruned it after it bloomed last spring.

==>>> patience grasshopper ... it really shouldnt surprise you in shrub time ... after the massacre .. lol ..

however.. i am guessing.. its not in full sun ... and its reaching out toward such ... if so.. it may never look the neighbors ..

that said... there are some much newer varieties that in form.. look nothing like the old versions .. and perhaps that is what your neighbor has ...

these things root in minutes ... if you are on good terms with your neighbor.. ask if you can harvest a few 6 to 8 inch pieces ... stick them in a vase.. and as soon as you see root nubs ... plant them into a pot of moist media.. and put in full bright shade ... [and if it leafs out.. a plastic bag for humidity might not hurt] .... and by fall.. you ought to have some nicely rooted plants.. you can plant in the garden ... others might just shove them in the ground .. and hope for the best ... if some water is available .. like right on your drip water system ...

i am sure you could verify the rooting process in a search engine ...

ken