There are four common terms that gardeners hear and use on a routine basis when discussing fertilizers or pesticides---synthetic, natural, organic and chemical. These terms are extensively used in gardening literature and popular media. As a Master Gardener and chemist I will define these terms and their implications for gardeners:
This implies that a substance used in a garden is "man-made" and not found naturally. For clarity, the term "synthetic" is better replaced with the term "inorganic" - that is, an inorganic fertilizer does not contain the element carbon (C).
Bottom line: A synthetic fertilizer may contain ingredients, such as, ammonium nitrate (NH4NO3), potassium chloride (KCl), sodium phosphate (Na3PO4), calcium sulfate (CaSO4), as part of its composition. However, because none of these ingredients contains the element carbon, this type of fertilizer is considered to be an inorganic fertilizer.
When we hear the term "natural", it implies that we are dealing with something that occurs in nature. A common misconception is, if it's nature-made, it can't be harmful to us or the environment. Well, this not totally true. As an example, consider the castor bean (Ricinus communis), which can be grown as an annual in our area. One of the products obtained from this plant is castor oil, which is used commercially and for human consumption. However, another component of this plant is ricin, one of the most deadly naturally occurring poisons known. A 500 microgram dose (about the size of the head of a pin) can kill an adult by injection.
Bottom line: Even though nature provides many wonderful things for the gardener, she does have a Jekyll and Hyde personality. Mess with her "Hyde" side, and one can be in big trouble!
Many gardeners proudly describe their practice as organic, implying superiority to gardeners who embrace chemicals. Many of the products that gardeners use fertilizers, herbicides, insecticides, fungicides - have an organic composition. But what does that mean? By definition any product that is truly organic (from a chemistry standpoint) must contain the element carbon. These products may also contain hydrogen, nitrogen, oxygen, potassium, sulfur, calcium, etc., but carbon is the key element that makes the product organic.
Bottom line: Many years ago a "wonderful" pesticide was used with great effect to combat malaria, typhus and other insect-borne human diseases and for insect control in institutions, homes and gardens. The interesting thing about this pesticide is that it is considered organic because it contains carbon. Most gardeners know this pesticide by its initials - DDT. This reality may be a revelation to some organic garden zealots.
The term "chemical" is probably the most misunderstood and misused of the four terms. It brings fear and panic to the hearts and minds of many gardeners. To ease a gardener's angst, it must be noted that every garden on this planet is filled with chemicals. Some are added by the gardener, but most are added by nature. Yes, nature is the main culprit in our gardens when it comes to chemicals. Trees, shrubs, perennials, weeds, lawns, leaves, mulches, soils, etc. are comprised of thousands of different chemicals.
Without nature's chemicals, our gardens wouldn't exist, our planet wouldn't exist, our universe wouldn't exist, and, this is really the bad part, we wouldn't exist! The next time you hear the term "chemical", don't run and hide, but calmly ask for specifics. Research the product to determine if it is beneficial to our health and the health of the garden.
Bottom line: Water (H2O) and oxygen (O2) are crucial to life on the earth. They are also chemicals.
The gardener does not need to be a chemist. But as an informed gardener, don't toss the generic terms synthetic, natural, organic and chemical around. Better to speak in specifics about products or techniques that you are employing in your garden.