One, it seems but it can't hurt to get others in case it's not enough. We're looking for a seed that's strong enough to grow there. We'll test them by using magic near it and see if it draws it in.

[He reaches into his coat and produces a journal. He tabs to a marked page and holds the book out. A drawing dominates the page. It's not too bad. Roughly enough to give a gist of the seed itself.]