^ I found this;
Calories Burned by Lawn and garden

gives an approximate figure for each activity. you might be surprised and perhaps could be burning quite a lot of calories ,depending on what you do I suppose. careful with your back and that the aches are not the result of improper bending down and lifting or that you are not hunched over for too long.
I have to be careful with bending down and tying shoes, have caused injuries to my back in the past doing that.