Once upon a time, at least when I was a child and budding
gardener, no one considered going down to the local garden
center to pick up fertilizer in a brightly colored pail or
plastic bag covered with images of gorgeous flowers or luscious
vegetables. There was no garden center, and most fertilizers
produced back then were for agricultural purposes, rather
than for the garden.
Most gardeners used compost, manure, or blood and bone meal
to provide the three major nutrients: nitrogen, phosphorus
and potassium. Blood meal provided nitrogen to promote vegetative
growth, while the phosphorus in the bone meal stimulated rooting
and blooming. As for potassium, the third major component
required by plants for healthy growth, there was always wood
Plants in a natural environment don't require feeding, having
adapted to their conditions, but when plants are grown intensively,
as in a garden or for agricultural purposes, soil is quickly
depleted of nutrients that must be replaced. This has been
known ever since plants were first cultivated, 6,000 to 10,000
years ago. If you were fortunate enough in those days to live
on the Nile delta or along the Tigris or Euphrates rivers,
you could rely on silt deposits from flooding rivers to maintain
soil productivity, but otherwise, farmers and gardeners in
ancient times had to find other ways to feed their soil.
The use of green manure crops, particularly legumes, was
mentioned by early Greek writers. Spreading manure or town
sewage on the land was (and still is) commonly carried out.
Plant ashes were also used to enrich the soil. Farmers in
those times knew these things worked, but not why.
Around the 16th century, chemists began to develop an understanding
of plant growth. A German chemist, Johann Glauder, put himself
at great personal risk collecting saltpeter (potassium nitrate)
from beneath cattle pens. He determined that it came from
the animal waste, and since what came out of the cow at one
end was directly related to what went in at the other, the
connection was made. After treating his garden with saltpeter,
Glauder observed large increases in the growth of his plants.