Longwood is spectacular, and well worth the trip, although I'm not sure if there would be much to see outdoors in February. To be fair the Conservatory is worth a visit any time of year, and the new fountain show is impressive (I presume it runs year-round).Longwood Gardens is in Kennet Square not far from Wilmington https://longwoodgardens.org/
Personally I like the historical stuff in Philly, and virtually all of the museums in DC are worth it.
Also another vote for Baltimore Inner Harbor and the Aquarium there.