baking your soil will only sterilize it, this will have nothing to do with the ability of the medium to hold a certain pH. You can bake your soil if you want to re-use the medium, but if you do this, make sure you open some windows in your house cause it will STINK!!! The oven has to be around 450 and the stench is nasty. The pH will be controlled held by something like Peat, humus, etc. If your using a pre-mix soil like the MG brand your soil will be considered 'hot' due to the peat that is in it. Best thing you can do for your medium is to go out and look for one that has manuare/humus mix and add some perilite to it for drainage. Some of the farmers here like to use the Fox Farm soilless mix, just be careful when looking for a medium because they all do act different. You need to find on that fits you, not anyone else. If you do use a medium that has nutes in it your going to be fighting that for a long long time during your grow and your plants will have issues right from the start.

Hope that helps.