When I was writing Planted I always knew that there would be a second book. I knew I couldn't tell the story I imagined in one. Then I thought it would be three books, a nice trilogy. But then my outline grew some more! I think Planted will be a tetralogy.
At first I wanted to title all the books with words that started with P and ended with ed. This was difficult! And I came up with Plighted for the third novel, and thought, "This is just ridiculous!"
Then another idea hit: How about name the novels so that together they form a short phrase? Has this been done before? I'm sure it has, I'm not that original. So now I'm thinking that they could be called Planted. Apart. Grow. Together.
Since I'm still rewriting the first of these books, all of this is a ways down the road. But I like imagining, and I think throwing out ideas like this ensures that some good ones will stick!