Homes n Gardens
Gardening Sources for Improving your Compost and soil.
boron
sources are: borax
calcium
sources are: oyster shells and gypsum
magnesium
sources are: epsom salts, dolomitic lime
Nitrogen
You get it free from grass clippings and leaves.
Other sources are: alfalfa meals, blood meal, fish emulsion, fish meal, guano and soybean meal
Nitrogen also stimulates vegetative growth as in healthy leaves etc.
Phosphorus
For that I usually buy something like Bonemeal.
Other sources are: rock phosphate, colloidal phosphate.
Phosphorus is necessary for fruit and flower formation and rapid stem growth in seedlings.
Potassium
Potassium helps to form stronger roots, stems and deepens the flower colour.
You get it free from wood ashes.
Other sources are: granite meal, greensand and sul-po-mag,