Explanation:

- Option 1: Stroking refers to the action of gently rubbing or moving one's hand over something. It doesn't fit the context of describing a garden.

- Option 2: Slouching means to sit or stand with an awkward, drooping posture. It doesn't relate to the description of grass in a garden.

- Option 3: Sprawling indicates spreading out over a large area in an untidy or irregular way. It effectively communicates plants or grass covering large patches, which fits the garden scenario well.

- Option 4: Stretching describes something extended or spread out. It can also work in the context of a garden with extended grass cover.

Option 3: Sprawling is the most appropriate choice.