The gardens are in Palazzo Pitti (Pitti palace). We spent a few hours in there walking up and down stairs and hills and looking at the wonderful gardens, statues and fountains. And the veiws from the gardens are absolutely fabulous.
The tickets are 7 euros each(under 6 is free) and the gardens are huge. We walked around for 2 1/2 hours and didn't see everything. We got a bit tired and decided to head back to the apartment.
It has been hot but not much different to Brisbane in Summer infact the buildings are much cooler because the walls are so thick.
I recommend the gardens to anyone coming to Florence for a visit.