Goosebumps Stay Out of the Basement

Dr Brewer is doing a little plant testing in his basement. Harmless really. But Margaret and Casey are worried about their father. Especially when they "meet" the plants he is growing down there. Then they notice that their father is developing plant-like tendencies.

Is it just part of their father's "harmless" experiment? Or has the basement turned into another little shop of horrors?