Wear ankle weights on your less intensive cycle to boost intensity.

Jump rope.

Stair climbing with some weight in a backpack.

As you are a keen gardener I'll bet you have a tub 40l+. Fill it with soil and carry it around. If you really want to make it heavy fill it with water which is far more dense so 1l will equal 1kg. Something like a farmers walk will get your heart up and tax your leg and back.

Ballistic movements like box jumping if your knees are ok. If it's too easy add weight so it becomes hypergravity training.