How many times can you harvest?

Is it possible to just take the buds of a plant and keep it in 12/12 light cycle and let it grow again then harvest, grow, harvet, etc... without revegging?

What I basically want to do is just keep a plant and slowly harvest it whenever i need weed...

Oh and has anybody tried that miracle grow spike stuff? It's like a small spike you stick next to the root and it gives the plant all the nuts it needs?