Three Essential plant Elements - NPK

Three Essential plant Elements

Essential Plant Elements and Sources of
Nitrogen, Phosphorus and Potassium

Is a part of chlorophyll and protein molecules in the plants. Plants low in nitrogen will produce yellow leaves and hardly any new growth.

Sources of Nitrogen:
Manure is a good source of nitrogen. Hot manures like, sheep and poultry are high in Nitrogen than cold manures like, Cow and Horse manure.
If you are able to buy fresh manure it's better to compost it for at least three to six months. Using it right away without composting first it could potentially burn tender plants and even killing seedlings.

Other nitrogen sources are: bonemeal, bloodmeal and cottonmeal. Cottonmeal will lower the PH of the soil, though. So, if you don't have acid loving plants, maybe cottonmeal is not for you.
Grass clippings and chopped up leaves will also add nitrogen to the soil and provide Humus to the soil.
I usually just compost my leaves and grass clipping and add them to the garden in the fall or when the compost is ready.

Phosphorus is necessary for flowers and fruit formation. Phosphorous deficiency shows up as or red discoloration on the leaves.
Sources for Phosphorus
I usually use bonemeal, because it's a good source of slow-release of Phosphorus.
It works well on flowering spring bulbs and it will also raise the PH of the soil and should not be used on acid loving plants.

Potassium helps to deepen the flower colour and form stronger roots and stems.
Deficiency of Potassium will show as a yellowing of leaves and brown tips.
Sources for Potassium are: Greensand, Granite Dust, Sea Weed, Wood Ashes and Langbeinite from New Mexico.
Wood Ashes tends to raise the soil PH and should not to used on acid loving plants.