Wildred, you can do that but, this is easier and involves a cheat or two. This is how EA made them, I think.
1. Go into edit mode.
2. Click on desired empty lot.
3. Its details should come up. Click on a bench or a button that says change lot type.
4. If community Garden is not an option, choose whatever you want.
5. Now click the building tools on the details.
6. Type in testingcheatsenabled true, then buydebug.
7. Go into buy mode, go into catagory selection, click the question mark, find the tab that looks like a plant or grass. It has all plants in it, just click them and put them down. You can also get seed, insect, fish, gem/metal spawners.
8. Finish building and decorating.
9. Save and go back to your sim.
I have never upoladed a lot but Downloading works best if the lot you want will fit exactly on the same size lot, eg. a house is a 20x30, that you downloaded, it will be easier if you place it on another 20x30 empty lot.