The Plant That Ate Dirty Socks by Nancy McArthur, 1988.

Michael and his younger brother, Norman, share a room, but it’s not a peaceful arrangement.  Norman is a neat freak, and Michael likes things messy.  Michael’s always saving random things that might turn out to be useful later, although how useful they are is questionable because it’s hard to even find anything in his pile of junk.  Michael also likes sending away for random things in the mail, like toys that require him to save a certain number of box tops.  Often, by the time these things arrive, he’s forgotten what he sent away for.

One day, Michael gets a couple of seeds in the mail that he doesn’t remember sending away for.  He plants one himself and gives one to his brother to plant.  The seeds come with a set of instructions, but Michael soon loses them, and the boys are left to care for their plants themselves.  Norman is very regular in his habits, watering his plant daily with his squirt gun and giving it the proper amount of plant food.  Michael is more experimental, dumping plant food on his plant haphazardly and even giving it bits of human food from time to time.  The boys have fun with their plants, treating them like pets, but soon, it becomes obvious that these aren’t normal plants.

It starts when socks start disappearing from Michael’s half of the room.  With Michael’s messiness, he often has to dig out his dirty socks from the rest of his stuff, but even after Michael cleans up his room, he still can’t find all of his socks.  The boys suspect that someone is stealing them, so they try to sit up at night (disguised as a robot and a gorilla, as if that would help) to find out who the thief is.  That’s how Michael discovers that his plant is actually eating his socks.  They try an experiment and discover that Norman’s plant also eats socks, except that Norman’s plant prefers clean socks, and Michael’s plant only eats the dirty ones.

When the boys demonstrate to their parents that the plants are eating socks, their mother wants them to get rid of the plants immediately, but the boys plead for their pet plants (which they name Fluffy and Stanley).  Michael promises to keep his half of the room neat from now on to keep his plant from eating anything it shouldn’t and proves that keeping plants for pets, even ones that eat socks, would be less expensive than keeping a dog or a cat, especially if they only buy cheap socks.  Reluctantly, their mother agrees to let them keep the plants, but their father forbids them to tell anyone about them because everyone will think they’re crazy.

However, with people at the store wondering why they’re buying so many socks, Michael’s friend Jason spending the night, and the upcoming science fair, for which Michael still needs a project, can Michael keep their weird plants a secret?  Does he even want to?

One of the things that I remembered from reading this book as a kid was the part where they invent Fudge Ripple Pancakes.  It starts because they were making up code words to use when talking about their plants, and someone overhears them saying “Fudge Ripple Pancakes,” so they have to make up a recipe to go with it.  The recipe isn’t exactly included in the book, but basically, it involves adding chocolate syrup to regular pancake mix.  The boys try it themselves and decide they like them.  Norman has a large squirt gun, kind of like a Super Soaker (but called by a different name), and he uses it to both water his plants and squirt syrup on his pancakes.

This is the first book in a series.