Hi again,
First I agree w/ stinky that if you plan on using one, the vermiculite is less noticable outdoors than the perlite. However, the perlite probably works better as a light loosener. As I said though, I think you will have a better time of it if you concentrate on adding organic composts instead of inert type looseners. Using an inert type loosener in your soil works a lot better in indoor container planting than it does outside directly in the dirt. Out in the ground, you will have the best grow by adding compost. Also add some water crystals and either an organic fert or a timed release type chem fert. The advantage to using chems is they are less likely to attract pests. Get either a battery PH meter or at least a cheap vial type kit. Either can be found at ANY garden store. Sounds like you usually have a good amount of rain, so you should have a decent grow with little or no watering. Soil sounds like a decent starting point.