Night Photography: Class 2

So I was looking forward to our first "location" shoot. We met down in Malaga Cove in Palos Verdes Estates for our second night photography class. I concentrated on two subjects: the Neptune fountain in the center of the plaza and a large pepper tree. I spent some time working on how shutter speed and aperture affects the photo. I had difficulty shooting Neptune as I was trying to shoot at a lower aperture while keeping a long exposure without washing out the marble statue. I was hoping to include the clouds behind the fountain but wasn't able to. We then started to play with flashes in attempt to back light the fountain. Due to the powerful spot lights that illuminate the statue, I could not get a decent photo. We then moved to the tree where we worked on "light painting." Although I am pleased with the shot below (Red tree), most of my other shots came out too bright (too low of an aperture) and then too dark (too high of an aperture) after adjusting my settings. I think I understand this concept and would like to try this again. I took entirely too many photos which I ended up deleting nearly all. Here are the shots that made the cut:
8 second exposure, f/14, 55mm, ISO 400
1 second exposure, f/4.5, 50mm, ISO 400
1/2 second exposure, f/9, 46mm, ISO 400
28 second exposure, f/8, 50mm, ISO 100
36 second exposure, f/8, 18mm, ISO 100