Max level of a gardener

What is the maximum level of a gardener? Does max level depend on whether the gardener is common, rare or epic or is the max level the same for all of them?

It’s level 30. If you want to convert vouchers to cards, the costs are different for each rarity. There might be diminishing returns from level 20 to 30, but that is not the case for all of them. At level 30, the cards will still say e.g. 3/100, but that is just for new cards to be stored properly. 100/100 will not yield level 31.