Moroccan Mint advice

I purchased 3 Moroccan mint plants about 3 years ago, following a trip to the country and consuming copious amounts of the delicious tea. However, i have really struggled to get a good harvest since the first year.
As a background, i have them in terracotta pots with some gravel at the base (i am aware of mint's growing habits, hence the pots). I would water them as and when the soil seemed dry, but apart from an odd feed have done little else with them. At the end of the growing season, when looking untidy, i have cut them right back. The pots tend to be in a sunny position and relatively sheltered from the wind
Last year i was very disappointed with how little Moroccan tea i was able to make, having found a fantastic recipe which i found to taste very authentic.
Any suggestions would be appreciated.

 

Is Moroccan mint an actual mint plant, I've not come across it, but if it is I would suggest repotting, it's quite a hungry plant and soon uses up nutrients in a container.
Normal mint also needs lots of water. .

 

I believe Mentha Spicata var Crispa is its actual variety name. I will look to repot it and see how it does. Thank you @pete .