I must say I'm a bit confused by your query. It sounds like you want to run a single factor experiment (aka OFAT). When you add 1 factor to the customer design platform, it will create a design using coded levels (-1, 1). You can use any actual values you want for these coded levels (use the upper and lower limits as the actual actual values).
Perhaps you don't want to run an experiment, but want to collect variable data on the agitation rate (any actual values between the limits) and use regression to analyze the relationship between agitation rate and Growth? In which case, collect the corresponding data in 2 columns in a JMP table, one for agitation rate and one for growth, then a simple fit Y by X platform should help to perform analysis.
"All models are wrong, some are useful" G.E.P. Box