For plants and vegetation it would be Lush. Luscious. Lush is also a slang word for a drunkard, from the 1790's and early 1800's

I don't think we'd use 'luxurious' to describe plants. We do use 'luscious' to describe plants, greenery, a jungle or landscape....it would describe a rich, green, vibrant place with plants. If you're specifically talking about expensive or rare plants, we would use 'exotic.'