I am wondering if I can purchase some small starters of various grass and start them inside like I do with my perrenials and annuals. I guess the reason that I am uncertain is that I know some of the warm weather grasses won't grow below a certain temperature. If I can start some of them now, I will be able to transplant larger plants come spring.
I am especially wondering about karl foerster, and several dwarf miscanthus, and fountain grasses. All of these grasses would be perennials in my zone. I would like to order some now from Santa Rosa gardens if this works.
Grasses you would buy from Santa Rosa are very likely to have been grown on (the industry calls it finished) from liners (flats) of grass plugs which they buy from growers. This 'finishing' involves potting the plugs up into larger containers, in which they will ultimately be sold, and growing them on to a salable size, in greenhouses.
As long as you can provide the appropriate conditions of light, heat, humidity and nutrition, you can grow smaller grasses into larger ones indoors. The problem is the conditions. Most houses don't have enough light and humidity. You can provide light pretty easily, with flourescent fixtures and timers, but humidity is not as easy to provide.
The grasses you list, from Santa Rosa, are appropriately sized for installation in the ground, or in larger pots, and growing outdoors. I think you could successfully grow them outdoors, starting in April, in your zone. The 'Karl Foerster' will start showing growth earlier than the Miscanthus and Pennisetum, but all will put on good growth this year. I doubt if growing them indoors for a couple of months would add much to their ultimate growth this year, and may indeed diminish it, unless you can provide proper conditions.
I grow Pennisetums and Miscanthus from seed, sown in March, and germinating outdoors in April. These seedlings reach 12-18" in height, and some even bloom, in their first year. These are species plants, and not the named cultivars.