Located at the busy end of York Road (just outside of the beltway), Watson's Garden Center has been a Lutherville institution for over a quarter of a century. I remember going here as a child and I still stop by even though I no longer live anywhere near it.
As garden centers go, it's not bad. It covers a large area and has an adequate selection, but overall I prefer Valley View Farms just down the road. With Valley View in such close proximity, Watson's just isn't able to keep up, so rather than compete directly, they are turning to other areas for specialization. As a result, they are becoming less and less a garden center and more an "outdoor living" store. They are a local dealer of the Rainbow play systems (overpriced, in my opinion) and have opened a fireplace and patio store as well.
If you are looking for a really good selection of plants, go to Valley View or Garlands, but if you don't mind a more limited selection, Watson's is fine.