as some foods are more nutritious than others, some soils carry
more of the six major (and eight minor) nutrients that plants
need to survive and thrive. Plants need large amounts of certain
nutrients—called macronutrients—and small amounts
of others, called micronutrients.
Fertilizers are concentrated nutrient sources.
So-called straight fertilizers consist of a single nutrient,
while compound fertilizers contain a blend, sometimes tailored
to a particular plant’s specific needs. Organic fertilizers
are made from formerly living things that are rich in nutrients—yummy
stuff like blood meal (dried animal blood), bone meal, feathers,
guano, and kelp, to name a few.
Of all the nutrients, potassium, phosphorous,
and nitrogen are most important—and most likely to get
depleted in soils—which is why you’ll find them included
in most compound fertilizers. (The label may say N-P-K, for nitrogen,
phosphorous, and potassium.)
Do you need to fertilize? Yellowing, feeble
growth, and curling or scorching of leaves can be signs of nutrient
deficiencies. But disease or the wrong pH can cause similar signs.
If in doubt, a soil testing kit can shed light on the status
of your soil’s nutrients.