how to charge for weekly hand weeding in commercial bid?

[GrayR84]

We are putting together a bid for a commercial property who also wants a price for weekly hand weeding of the mulch and rock beds at their property while we are on-site for the mow. How do you figure out how much to add to the weekly mowing price for a 7 month bid for a service like this? It's a decent sized property, and it could take a while if it's weedy, and theoretically not much time if we're doing it each week / in the autumn time when things grow slowly. With it being winter it's hard to tell exactly what it will need.