Orchard grass/readigrass how much?

I am thinking of getting some orchard grass or readigrass to supplement Radish's hay as she really like the orchard grass sample pack I got her.

I wondered how much of this should I give her a week as I understand I can't use it on it's own only in addition to other hay.

Thanks

I give a handful a day of orchard grass which is fine to feed freely. Readigrass is quite high in calcium so best to feed in ocassionally.

The Oxbow Orchard Grass Hay I feed unlimited to my bun. He loves it and eats it now in place of the Timothy Hay.