Why five seasons?
A garden can look good all year round. There are a lot of businesses already called 'four seasons' including some gardening ones. Five seasons hopefully goes one better.
In gardens, early summer is like a distinct season of its own, with its Peonies, Irises, Lilac, Foxgloves, and Mock Orange Blossom.
Alternatively, I have heard the fifth season described as the time taken to enjoy the other four.
Ultimately, as an organic process any division into a fixed number of seasons is artificial.