I came across the sentence while studying linguistics in the 70s, and it has occupied a small and dusty crevice in my brain ever since. I was reminded of it while looking through Wikipedia for something related to a comment I was making on another site, which contained a reference to it, and I was drawn into reading the whole article.
Over the years, there have been several (usually unsuccessful) attempts to cast the five words into a sentence that would give them genuine meaning, but of course it is very difficult - impossible, in fact, unless one uses the words metaphorically. Stanford University held a literary competition in 1985, in which contestants had 100 words or 14 lines of poetry to make it meaningful. One entry, which may not have been the winner but should have been if it wasn't, was from one C M Street. I found it utterly charming and uplifting.
It can only be the thought of verdure to come, which prompts us in the autumn to buy these dormant white lumps of vegetable matter covered by a brown papery skin, and lovingly to plant them and care for them. It is a marvel to me that under this cover they are labouring unseen at such a rate within to give us the sudden awesome beauty of spring flowering bulbs. While winter reigns the earth reposes but these colourless green ideas sleep furiously.