Low season is best described as progressively cold and rainy with some nice weather thrown in too. Click on the Climate link for more on Greece's weather pattern and how to make the most of it.
Fewer people travel during low season for weather reasons and work schedules. Consequently far fewer cruises and tours operate. Its not worth it. Many larger hotels will close too for the same reasons. Many Greeks and Albanians return to Athens from working the summer hot spots to their winter jobs if they have one. Therefore many Greeks you see on the Greek islands are transients working there for the season. Crete is a notable partial exception to this rule as is Rhodes and both have large local populations. If you look at the map you'll see that a good portion of Greece is farther south than the hump of North Africa. Crete and Rhodes are the warmest parts of Greece and consequently have longer seasons. Crete is the southern most land mass of Europe.
Greece is at its most beautiful this time of year and the spring flowers bestow the country side, a real fairytale feel. The most isolated mountain tract or decayed ancient ruin can be thrown into an entirely different light by spring flowers. Greece has over 6,000 species of flower and almost 700 of these occur only in Greece. This is possible because the many mountains create micro-climates which encourage independent development. Over 450 species of birds too, either live in Greece, or rest here while migrating.
By the end of March the rainy season is winding down and by April, while it still may rain occasionally, the sun will do more than just peek out of the clouds that same afternoon. This is my favorite time of year in Greece because I know it will only get better and warmer. For those with the time to travel, such as students, this is the best time to get to know Greece. If you happen upon a spot you really like you can always stay longer too!
Ferry schedules will be increasing in frequency so you can get to out of the way places with more facility and take exploratory day and weekend trips. Most everything else will be opening as mid-season turns to May and June. If local businesses are looking for help this is the time to make yourself available.
If you hang around long in one spot you'll see more and more visitors start to arrive until finally you realize that high season is imminent. Every few days you'll notice a pattern of new recruits strolling the streets or eating at the local taverna or at your favorite bar or beach. Sitting in one spot is a great way to meet people as they come to you. Still for this you need time and students are the most likely to have it.
High Season is July 15th thru August and when its best to have made your reservations well in advance. This doesn't strictly hold true everywhere in Greece but it is true for popular destinations like Crete, Rhodes, Mykonos and particularly Santorini, one of the most popular island destinations in the world.
In general the Cyclades are always well visited in high season as are the rest of the Greek island groups each having its most popular islands. The Greek mainland is where you'll find more open spaces and far fewer tourists during high season. I don't mean the major mainland archeological attractions like Olympia or Mycenae in the Peloponnese or even Delphi only 3 hours from Athens. Those are served by tours buses and you cant escape the crowds.
I mean the semi-abandoned villages of interior central and northern Greece. Many Europeans have purchased and restored houses in these villages and are bringing them back to life at least for part of the year. They cost more or less depending on location. Also the Greek inheritance laws sometimes make it necessary to track down partial owners in other countries like Australia in order to get their signature on bills of sale.
As a matter of fact this is an undiscovered aspect of Greece of which I will write more on other pages.
Fall is another off time to visit Greece. Its not as inexpensive as winter but it is a bit less than high season. Retirees and people with money and time to spare come to Greece during the fall. It has the same advantages as spring except that the local population is tired more or less depending on how busy the high season was. They may not be quite as enthusiastic or perky.