Look at the plants in the garden and you will see if are anchored in a fertile soil or if they have trouble finding enough water and nutrients. To flourish and sprout, the flowers should have sufficient amounts of minerals, air, water and organic substances. Sandy soil, for example, is slightly porous, allowing the passage of water and is easy to work with, but does not retain nutrients.
You can determine the quality of the soil in your garden quickly and easily, with finger test: Dampen a piece of soil and rub it between your fingers. If the soil is running through your fingers, it is sandy. If you can knead the soil in a crumbly roll shape, then is a mix between sandy and loam soil. Clay soil forms a firm roll. The best way to find out if your garden soil is acid or alkaline pH is using a soil test.
Good soil has earthworms.
A magic remedy to improve the quality of all garden soil is humus. If in a heavy clay soil you mix humus or bark or sand, they will improve aeration. However, the most avid and reliable producers of humus are microorganisms that abound in the ground and work hard. One gram of soil rich in humus hosts over a billion tiny bodies. They loosen the soil by digging through it and transform organic matter into precious humus. The most remarkable microorganism of this kind is the earthworm. Therefore, the more earthworms in the soil, the better. A large number of earthworms is a good indicator of quality soil.