With soils there is not a one size fits all. There is a plethora of mixes of soil available so choosing can be a daunting task. And not all soils are created equally. Cheap soil mixes don't have the structure and often used recycled ingredients from arborist waste shredded as mulch and lacks nutrients or aeration. Often nursery stock is sold in material to save cost, but in the long run plants will suffer unless transplanted into a more suitable substrate.
Good soil will consist of materials to help with both water retention and aeration, a proper balanced pH, and a charge of nutrients to help them thrive. Some soils also include beneficial fungi to help roots grow and establish themselves.
So how do we choose a good soil? First we want to consider what we are growing and what our goal is. For fast growing plants such as vegetables or even cannabis, we want a soil rich with organic materials such as earthworm castings, fish meal, feather meal, guanos, mycorrhizae, and buffering agents for pH like dolimite, or oyster shells to say the least. These soils will also have perlite or pumice to increase aeration to help keep the soil structure.
In other incidences we may want to grow our favorite houseplants and here soil structure should be our goal. We aren't after nutrious consumable plants but long term thriving growth. Yes nutrients wil be important, but we want plants to have good drainage, and be able to sustain the plants without a lot of fuss. Additoinally wit the rise of popularity of exotic house plants especially, blending your soil is often ideal to buying cheap mixes from a hardware store example. These custom blends are available but its not uncommon to want to doctor up the soil for your specific watering needs and grow conditions. For example I will offen add more pumice to my soils to assure I don't over water.
Now with all this said lets look at some common inputs and purposes.
Peat: This is the most common base used and is what the other inputs are added to. Sometimes you see this as cooc peat. Although a good base substate coco needs buffering and tends to either leach salts and can rob the roots of secondary nutrients such as calcium and magnesium.
Perlite | Pumice: These are great and more often than not an extremely important to add texture and aeration to soils. For aeration soil mixes will often use about 20-40% to final compostion for proper structure.
Worm castings: Earthworm castings are great way to add beneficial microbes to the soil and help with overall health of your plant growth. They will provide some nurtients such as nitrogen.
Rice hulls: These are over looked and a great additive to soils. They help wit structure and as the break down they provide a charge of silicate. This helps with stress from things like heat and drought.
Mycorrhizae: Essesentail for root developement. This fungul innoculent increase nutrient uptake, drought tolerance and rapid growth, Always recommended when transplanting for faster establishment.