I've been most successful with A Nice Garden in spring and summer. Make sure you aren't aiming at the ground. I tend to keep the camera at "eye level" with the photographer, and just slowly turn in a circle. Sometimes it'll pop up for a second, sometimes not.
Another option, depending on where you're playing, is to go to the community garden.
A Nice Garden does not consist of harvestables, it consists of the plants found in Build Mode. You could try making your own, if you have the simoleans to burn; if so, I recommend to avoid any plant that will be named in the photo itself (red rosey, hydrangea, sunflower, white roses, etc).
Edit: Also, the garden itself may not necessarily register from your own lot. I've had it register from the neighbor's lot, or from a lot just down the street.
