Chemical/synthetic fertilizers are manufactured using synthetic substances that usually contain highly concentrated forms of nitrogen, phosphorus and potassium (these are the N-P-K values listed on the fertilizer packaging).
These fertilizers work quickly because they feed the plants directly. But they do come with a downside – they do not improve the soil itself and they can, over time, even destroy the beneficial organisms needed for healthy soil. When you use large quantities of this inorganic stuff over and over again, its byproducts will actually build up in the soil and in time they can hinder plant growth.
Organic/natural fertilizers often use alfalfa meal, cottonseed meal, or fish emulsion to provide nitrogen; bone meal or rock phosphate to provide phosphorus; and kelp meal or granite meal to provide potassium.
The downside here is that they work much more slowly, first breaking down in the soil into forms that the plant roots can more easily absorb, then making their way up the plant roots to your hungry plants.
Organic/natural fertilizers, on the other hand, don’t feed the plants directly but rather add essential nutrients to the soil where they become available to the plants, more slowly, over time.
Understanding the Basics about N-P-K
While there are also many important micronutrients in good fertilizer, it is understanding the “big 3,” the N-P-K, that is the key to making your own effective fertilizer at home. The N is for nitrogen, the P for phosphorus, and the K for Potassium. Each has an important role to play in the health of your garden.
Nitrogen is the nutrient plants use most to grow large and lush – tall stems with lots of good leafy growth. If you examine the N-P-K content of commercial products that advertise “miracle growth” you will find there is no real miracle at all – the amazing growth is due to a balanced but high N-P-K ratio with a hefty amount of nitrogen in the mix.
Phosphorus is needed to grow strong healthy root systems, and to promote vigorous flowering. Commercial “blooming” mixes are usually high in phosphorus.
Potassium helps with plant growth, protein production, plant hardiness, disease resistance, insect resistance and efficient water use. Plants without enough potassium grow slowly and can have yellow leaves.