I have very fertile, deep alkaline loam soil on a clay sub soil in a gently sloping garden so drainage varies. I add my own garden compost every time I plant, be it single plants or a spread to revitalise a bed. I scatter pelleted chicken, cow and/or horse manure every spring and add it to the hole when planting hungry plants like roses and clematis. These plants also get a dollop of specialist rose or clematis food in spring.
Veggie beds get garden compost every time I clear a crop and scatterings of pelleted manure at planting time and in spring for the fruit bushes, rhubarb and strawberries which are permanent crops.
Any soil, be it sand, loam, stony or clay, free draining or moisture retentive, can be improved by mulching with well rotted manure or compost every autumn and after planting something new. As said above, good soil structure is essential to plant health and soil fertility an dthe ability ofplants to take up the nutrients available..