Right, so "a wind-up for the horticulturalist?" is the whimsical definition — a garden hose, of course, being the thing gardeners literally wind up onto a reel. For the wordplay: "kid's" gives us RAG (to kid or tease someone), and "knocked over" tells you to reverse it, turning RAG into GAR. Then "shed one rebuilt" is an anagram (that's the "rebuilt") of the letters in "shed one", which sorts itself out into DENHOSE. Stick GAR and DENHOSE together and you've built your GARDEN HOSE.