This is lovage, a perennial herb that tastes very much like celery. I started some seeds in the greenhouse and transplanted it into the garden last year and it was kind of spindly and thin. It struggled. This year it looks like it's going to do quite well.
This photo was taken last week after an extended period of highs in the upper 60s and lower 70s (fahrenheit) and lows in the 40s. We've had snow for the last 4 or 5 days, and for the most part my lovage is wilted on the ground, with a few new leaves bravely sprouting. I'm confident that when the temperatures warm up the lovage will flourish.
When I taste the leaves I cannot tell the difference between lovage and celery leaves. I've read that you use it "just like celery" but last year the stems were thin and woody. I couldn't imagine those stems in my cooking and they certainly had no place in my salads. It hasn't yet grown enough to see if the stems will be larger and more tender this year.
At any rate, I intend to harvest and dry the leaves, as I would oregano or basil. That should make for some nice seasonings for winter soups and stews.