On the day of the meeting, who arrives in the morning at Gatsby's house?

A landscaper or gardener arrives at Nick's house. From this, we can infer that Gatsby thought Nick's house needed a bit of spucing up.

The day agreed upon was pouring rain. At eleven o’clock a man in a raincoat, dragging a lawn-mower, tapped at my front door and said that Mr. Gatsby had sent him over to cut my grass.