This is a larger-format picture book, in full color, with illustrations that cover most/all of each page. I read it in the early- to mid-80’s. There’s a farmer who grows vegetables and something happens to his farm where he starts growing GIGANTIC vegetables. There’s a bad guy (I think he’s dressed in a black suit and might have a black top hat?) who wants to get his hands on the farm or the stuff that makes the farm miraculous. I can’t remember if the thing that makes the vegetables big starts to affect the farmer’s kids or not?
Thank you for reading!