Answer: What you describe sound like suckers emerging from buried roots. This is a normal growth habit for forsythia - it tends to want to colonize an area by producing lots of suckers. You may be able to sever the root between the sucker and the main stem of the plant by digging straight down with a sharp shovel. Once you've cut through the root you can dig the sucker up and replant it. It should have no trouble growing for you. You can do it now or you can wait until next spring after it has finished flowering.
Best wishes with your garden!
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