When designing an experiment how large should i make theplot

[mmmmmm]

in general what factor would determine the appropritate scale?

I dont understand..what are plots and what determines how large or small they are?

[AstusAleator]

A plot is a cordoned-off section of the test-area that you will be getting your data from. Using a plot gives you the advantage of assigning relevant reference data to your collected data. For example, if you are trying to determine the total vegetative production in an area, you can make a plot of a known size, find the production in that plot, and then expand your results to extrapolate the total production of the area.
If the area in question is 300 square meters, I can put down a 1 square meter plot, determine production in that plot, and then multiply by 300.

As for the size of a plot, that depends on the variables being measured, and the amount of area being assessed. If you are counting bacterial colonies on a petri dish (there are better ways to do this than with plots, but this is just a micro-example) you might use a 1 square centimeter plot or smaller! If you are counting blades of grass on a lawn, and the density of the blades seems pretty uniform throughout, you could use a 1 square foot plot (though I would take data from more than one plot, average them, then extrapolate). If your project scale is over an entire landscape, then you might want to use 600 square meter plots or even larger, and lots of them.