Wax and wane
Definition 1 of 2
Pro Tip 1/3Not Literal
The phrase doesn't refer to physical growth, but to changes in intensity or size. 
The crowd at the festival waxed and waned as the day went on.
Pro Tip 2/3Emotional Variation
Can describe shifts in feelings or attitudes, not just measurable things. 
His passion for the hobby waxed and waned over time.
Pro Tip 3/3Temporal Changes
Often used to talk about changes that happen over a period of time. 
The town's prosperity waxed and waned with the seasons.