1. The grass grows thick in the garden.

Question

2. The grass grows thickly in the garden.

3. The grass grows thin in the garden.
4. The grass grows thinly in the garden.
(Which expressions are correct and grammatical?)

Answer 1

Since I could say, "The grass is thick [or thin] in the garden," and keep the same meaning, I would use sentences 1 and 3.

http://www.chompchomp.com/terms/linkingverb.htm
Scroll down a bit and read all about the "multiple personalities" verbs!!