As we are unaware of where in Australia you are located, it is hard for us to discuss specific schools and their associated programs. It’ll be in your interest to find courses in your desired geographical location and then fill out the green Contact Form to ask any specific queries you may have.
There are a number of short courses in Australia relating to your interests. For example, the NMIT in Melbourne has a Basic Carpentry course, as well as a Hand and Power Tools for Woodworking course. Cengage Education also has a Carpentry and Joinery short course.
Of course there are also TAFE certificate accredited courses in carpentry all over Australia, but these will last for at least one full semester when done full-time, or its part-time equivalent.
As for gardening short courses, the Gipps TAFE in country Victoria has a No Dig Vegetable Gardening class, while the South West Institute of TAFE has an Age Friendly Gardening program. Again there is a number of TAFE Horticulture programs all over Australia you can choose from, but these are much more intensive than a quick short course.