There aren't really any gardens of note on Malta. There are a couple of grand houses with pleasantly designed outdoor spaces, but nothing that cannot wait for another visit. The island was once described to me as a 'sunny Portland' (in Dorset UK for any Americans out there). I see where the statement came from, but do feel it to be a little harsh.
The east coast of the island is very developed, and probably best avoided, but the west is wonderfully wild. It's a small island, that can take only a day to drive around, but the scenery can be breathtaking, with everything being covered in wild flowers.
Even early in the year plant life is colourful and lush, one just has to venture out and see with open eyes. Some of the roads though can be a little challenging as you can see.
However, not as challenging as driving to the airport during a cyclone!