Depends on how much you add.

Dan

Depends on the rock. Granite dust is acidic. But you would have to add a lot of it to change the soil pH.

If your soil is loam with 5% organic matter and the remainder composed of clay, silt and sand minerals, then plants will do very well with a pH of 7.0. The plants might do marginally better if the pH was 6.0. They might do marginally worse of the pH was 8.0.

But there are other factors - fertilizer, rain, sunshine, weed competition. You just need to grow stuff and enjoy it and not get all wraped up in ideal conditions. Nobody has ideal conditions.

You are going to make mistakes, but that's how you learn. I have been growing plants for more years than I want to admit and I am still screwing up. So just go out there and get on with it and don't worry about ideal soil pH.

Here is a link that might be useful: Soil

A soil with a pH of 7.0 is only slightly higher then the optimal 6.2 to 6.8 pH most all plants prefer to grow in and the soil pH that most all soil niutrients are most readily available in. A pH in the 5 to 6 range is getting quite acidic and into the range that acidci soil needing plants such as Rhododendrons, Blueberries, Camelias, etc. need.
What nutrients will the rock dusts be replacing? Are those rock dusts really needed? What did a good, reliable soil test say about nutrient levels?

Where will you get granite or basalt dust? I havn't found it to be readily available at any kind of reasonable price.

What nutrients will the rock dusts be replacing?

Perhaps cobalt, yttrium, strontium, etc.? What soil test will likely show the trace minerals in a wide spectrum?

Perhaps many plants will grow without optimum levels of certain minerals, but our bodies can be healthier with them.

Be sure to check out the Garden-ville web site. Malcom Beck has a great book, "Lessons in Nature". It talks specifically about growing in alkaline soils. For example, he has performed tests which show superior yields if you lay down a clump of rock phosphate instead of working it in and then plant directly in it.

Here is a link that might be useful: Garden-ville

^ but I'm working with neutral soil, not alkaline. :confused:

You could draw an imaginary line down the middle of the garden, and put rock dust on one side. Then you could plant, and wait & see what the results are. That would be of great interest to lots of gardeners.