900 clicks a month off 31 posts in 10 months is a better posts-to-clicks ratio than most broad sites ever manage. You haven't niched into a hole, you've found a wedge.
The thing people get wrong about "too narrow" is that narrow is about the topic, not the audience. Your audience is anyone in a hot climate without a yard, which is tens of millions of people across the US southwest, Australia, southern Europe, India, the Gulf. That's not narrow at all.
Where you actually expand is outward from the same person, not sideways into unrelated gardening. What else does someone with a hot balcony want? Shade solutions, outdoor furniture that survives sun, small-space composting, watering while away on holiday, apartment-friendly tools. Same reader, adjacent problems. You'll double your post count without diluting a thing.
Don't start writing about lawns.