Even the Greek islands in the southern Aegean don't really come out fully from the chill of winter until May, though there can even be some balmy days as early as March, and the connection with nature and the elements is still very present in the Greek consciousness, the country having been largely rural until very recent times.
Hence, the coming of warm weather in May has long been celebrated in Greece, and there is even a fine folk song (with the name 'Mais', the Greek name of the month) which eulogizes the coming of the flowers, and then songs, the two words rhyming in Greek (louloudhia and tragoudhia).
On May Day people flood out of the big cities into the countryside to pick wildflowers for the wreaths that they will hang on their front doors until the 23rd of June, when when the dessicated wreaths are finally burned in a big bonfire. Farmers also make wreaths, but use cereal plants, such as barley or wheat as well as the branches from fruit and nut trees, which symbolize the wish for a good harvest. Sometimes they add a whole head of garlic to the wreath, to ward off the evil eye, and a thistle, to ward off enemies.
In the north part of the island of Evia (Euboea), there was a related custom in times of drought, in which a villager was adorned with flowers and tree branches, the latter including olive and walnut, a wreath placed around his head and a bell on his chest. He was called 'Piperia' (meaning 'pepper'-the vegetable) and was led by a group of men from house to house where he sang good wishes to the villagers.
May Day is also a big left-wing holiday, with big demonstrations in the cities. Perhpas the politicizing of May day came much later than the original purpose for the holiday.