4 ideas
Mary Lennox, a spoiled and sickly orphan sent from India to her uncle's Yorkshire manor, finds the key to a walled garden locked for ten years after her aunt died there. With the help of Dickon, a moor boy, she secretly restores it, and then brings her bedridden cousin Colin into it.
Colin's invalidism comes mostly from adults expecting him to die and from his own fixation on a spinal lump that does not exist. Once Mary flatly tells him there is nothing wrong with his back, the belief breaks, and his body follows his changed expectations. The book claims that fearful thoughts act like poison on the body and hopeful ones like medicine, so replacing one thought with another is a physical intervention.
Mary and Colin are sour and tyrannical because nothing has ever needed them and all their attention turns inward. Clearing weeds, watching bulbs come up and keeping a secret project going shifts their attention outward to a living thing that responds to their care. Their tempers soften as a side effect of being responsible for something, not because anyone lectures them.
The locked garden, Colin's shut room and Mr. Craven's closed-off grief are the same condition in different forms: something alive sealed away after a loss and left to decline untended. Read this way, restoring the garden and restoring the household are one process, and a place's physical state can be read as a diagnosis of the emotional state of the people who control it.