Soil Types

Most people prefer loose soil over heavy loam because it allows for faster growth of the plants. The plant will grow proportional to its root base due to potential for being toppled over by high winds. Loamy soil is nutrient dense but roots have a much harder time cutting through it. Also, most of the nutrients in loamy soil are bound up tightly and difficult for the plant to access without the addition of something like gypsum to break up the bonds in clay-type soils. Many people suffer from overwatering and loamy soils are bad for them on two fronts. First, they are inherently heavy so it makes a weight test difficult to perform. Secondly, they hold far more moisture than loose airy soil, which further compounds the issue of proper irrigation.

Another key aspect to growing this way is that the roots require oxygen for growth and the prevention of rootborn diseases. The more oxygen the roots can get the faster and healthier they will grow. In loamy soils the plant will develop specialized roots near the surface for this purpose, which is typically where people top dress. These roots aren't as efficient at nutrient absorption as the other roots so the nutrients have to make it further into the pot to be useful.

That being said, I have a naturally loamy/heavy clay soil where I live and found some of the best and most dense flowers I have ever grown came from mixing in about 20% of my native clay soil into my mix. I also used about 10% of the pulverized sand from about 10-15 feet down from when I dug a well. I wouldn't dream of growing in 100% native soil though because it's far too dense and would require extensive conditioning before being a viable option.

Would love to see some mixtures ratios :) I know there ppl out there growing in loam but is very small amount