With the information at hand, and assuming that Gloria was the daughter of that secret clan's family. Then, perhaps her gardening skills weren't just ordinary but backed by the super powers of her family.
Even if she didn't have any super powers, the fact that she was such a great gardener and gardening all by herself she could produce a lot of vegetables that could feed the whole clan, at least at the clan house every single day without fail. Such a great talent, if utilized well, one could go further. And in his case, if he were to use this excuse, then Simon, with his inflated ego might agree to let her go.
However, letting go wasn't easy. He needed to find a way to let Simon fall for his trap without him approaching the other first. Using his spies, Xander let the news spread of him wanting some talented gardeners and have some people close to Simon talk about it.
