Boy chalks beanstalk or garden all over the pavement/sidewalk of his town, possibly as part of an art competition. Then rain washes it away, leaving only what was done in an alley way.
Children’s fiction - read in 1980/1990s. He was given an allotted space to do his chalk art but he went up the walls and through alley ways etc. At the end it was all rained away.
Beautiful illustrations as I recall - not a chapter book but a child’s story book.