One of the great things about London Pride is that it can be happy in many different types of soil. If it has been growing quite well as it is, then there probably isn't any need to "improve" the soil - but if it seems to be struggling then you could add a little something to cheer it up!
If the soil is too rich it will spread a lot but also become more lax in its growth, which isn't so attractive.
Another case for a "happy medium"!!
