Do your plants know where their next meal is coming from?
There’s no finer sight than a pile of aged manure being dumped in the driveway. OK, not for everyone. Ugh, is the likely response from the neighbours, unless they’re also committed gardeners who appreciate the benefits that good, organic matter brings to a garden. That happened occasionally when my dad needed something to feed his roses. Fortunately, the immediate neighbour was of the same mind, and it really wasn’t that bad as aged manure, besides being a good source of nutrients, is practically odourless.
This was decades ago, a time when a trip down to the local garden centre to buy a bag of fertilizer wasn’t possible. There were no garden centres then, only a few plant nurseries, and most didn’t deal much in industrially produced fertilizer. In my summer job as a gardener’s boy at the big house in the village, I recall seeing bags of blood meal, bone meal and potash. These are forms of the three main nutrients required by plants, referenced as NPK — nitrogen, phosphorus and potassium. If you’re confused about the K, it’s from kalium, an old Latin term for potash.
Fertilizers that did eventually appear for use in a home garden were adapted from those originally developed for agriculture, but for most of history, the way to return nutrients to the soil for crops was to add compost, use cover crops, or allow pastures to lie fallow for a period. Spreading manure or town sewage on the land was (and still is) commonly carried out. They knew these things worked, but not why.
It wasn’t until the 16th century that early chemists began to develop an understanding of plant growth. Johann Glauder, a German chemist, collected saltpeter (potassium nitrate, a form of nitrogen and potassium) from beneath cattle pens and determined that it came from the animal waste. By close observation, a risky business, he’d figured out that what came out of the cow at one end was directly related to what went in at the other. After treating his garden with the saltpeter, he observed an increase in the growth of his plants, so it would appear that his soil was lacking these nutrients.
As further research by early soil scientists revealed the secrets of soil, the search was on to produce these three main components in commercial quantities. However, it wasn’t until the 1840s that other natural sources of fertilizer were discovered. One was guano, the nitrogen and phosphate-rich droppings of sea birds. It was shipped from Peru, but it was a challenge for the sea birds of Peru to meet the demand. Meanwhile, large natural deposits of sodium nitrate that provided nitrogen were discovered in Chile. Potassium was also provided by potash, a mineral mined in many locations around the world, including Saskatchewan, the world’s third-largest producer.
As for the phosphorus element, the other major nutrient in fertilizer, it was originally derived by grinding up animal bones — hence bone meal. Much phosphate is now produced from phosphate rock, mined from sedimentary deposits of petrified sea creatures, the basis of limestone.
Plants growing in a natural environment don’t require feeding, but when grown intensively, as in agriculture, soil is quickly depleted of these elements that must be replaced. This isn’t quite the same in garden soil where phosphorus and potassium are rarely lacking. In fact, the run-off from overuse is having a serious impact on lakes and waterways where phosphorus, in particular, causes abundant algae growth, which in turn produces harmful toxins. This is why most lawn fertilizers now contain little or none. Although these nutrients are popularly referred to as chemicals, whether produced commercially or from organic sources, as far as the plant is concerned, they’re identical.
Ideally, a soil test should be done before anything is added to soil. However, this isn’t always practical. I’ve never tested the soil in my garden where everything seems to grow well. I will sometimes add nitrogen, usually blood meal, as it’s the one nutrient that doesn’t stick around in soil. Otherwise, I prefer to keep it simple and rely mainly on compost. And of course, as my dad would say, there’s nothing like a big pile of well-aged manure.