If you are thinking of starting a rock garden, you will need to do your research and ensure you have the proper materials. If you end up using the wrong kinds of rock, your end result will not be as effective as you originally planned. It is ideal to use rocks that are obtained locally due to the fact that rocks that exist in your current habitat will function best in their natural environment in your garden. What kinds of rocks should you consider?
There is one type of rock known as the sympathetic stone, and it is called this because these rocks are sympathetic to the plant life and vegetation that exists around them. The quality of ‘sympathy’ a rock will give towards the plants around them depend on their porosity and capacity to store water and moisture. This kind of rock is ideal if you expect to plant vegetation and flowering around your rocks, as rocks that are able to absorb moisture will encourage roots from your plants to hug the rock and its surface deep into the soil. The most sympathetic rocks will be porous on the surface and if you pour water on them, it will easily absorb. If you are looking for sympathetic rocks, stay away from smooth surfaced rocks with close-grained textures.
The most ideal kinds of rocks are neither very soft nor very hard. Very hard stones will not be sympathetic to vegetative growth, and softer stones are considered impractical because they often will disintegrate quickly.
Granite is a type of stone that is used frequently because it is very easy to obtain. You want to find pieces that are shaped irregularly, and contain rough surfaces as they will serve the purpose you are looking for. Field stones that are used for home building are often located in areas that contain glacial deposits, and because of this they will contain smooth round surfaces that are not desirable for vegetative growth around them.
Limestone and sandstone are also ideal rock selections as they show some stratification on the surface with a grainy texture. These stones come in a wide variety of size and shapes and will work with the vegetation around them. If you find field rocks that are not too small and look a little weather beaten, they will be ideal as well. Field rocks are even more sympathetic if they also are covered in lichen or moss surfaces, and these will not only add to their vegetative qualities, but add character from an aesthetic stand point.
No matter how you choose your garden rocks, consider your purpose. If you only want aesthetic purposes but do not plan to plant much around them, the kind of rock you choose depends entirely on personal taste. For planting purposes however, sympathetic rocks are the best rocks to get when considering your rock gardens.