Despite similar functions there is a difference between a bag of commercial fertilizer and a bag of compost. Commercial fertilizers are fast-acting chemicals, nitrogen, phosphorus, and potassium, that feed plants for a short time, while compost is dead plant matter that decomposes to nurture not only live plants, but also the soil microbes that slowly feed plants by unlocking soil nutrients then dying and enriching the soil with their remains.
In a perfect world gardens do not require commercial fertilizers because healthy topsoil’s compost to sand to clay makeup is the perfect 1:1:1 ratio. Alas, local worn out native soil has been through the farming wringer. It consists of clay, sand, or sandy loam, a fairly infertile mix of sand and clay. If you can’t see a dark brown to black layer of topsoil when you dig with a spade, you may be down to the subsoil.
Ground with 30 percent clay or sand is a garden dream; 100 percent is a nightmare. Every year we amend or improve our little bit of Eden by adding sandy topsoil and bags of various composts. While Mother Nature runs her leisurely course we sprinkle in commercial fertilizers for a plant and microbe growth snack.
Stores sell a bewildering array of commercial fertilizers in boxes, bags, jars, bottles, and spikes. Some are complete (contain nitrogen, phosphorus, and potassium); some are incomplete (missing one or more element). Some are synthetic (manufactured chemicals); others are organic (dead organisms or parts thereof). Some are all-purpose, and some are specialized.
Gardeners can skip nutritional guesswork, and save money by purchasing soil testing kits from garden centers to get an idea of what’s missing in their soil mix. If you’re not a soil tinkerer you can have the county ag extension service analyze a soil sample from your garden.
While it is possible to give your garden the kiss of death by applying hot (fresh) manure, an organic fertilizer, more gardeners can tell you a sad tale about the time he/she killed an entire garden or lawn with too much synthetic fertilizer.
Bags of compost from big do-it-yourself stores tend to be chipped wood and tree bark. We use them to mulch, and over the year they decompose from the bottom up.
The speed with which 6” of shredded cypress or hardwood disappears before the naked eye boggles the mind. Be forewarned that roaches love to nest in pine bark, and there is such a thing as too much peat moss which tends to tamp out beneficial microscopic soil communities.
Other plant waste like used coffee grinds, vegetable leftovers, and fallen leaves and twigs all contribute to compost. Avoid meat wastes as they harbor pathogens.
Be serious about the ingredient ratios of perfect soil, and you’ll avoid a lot of problems. Feeding the soil is an art we learn by trial and error. When amendment ceases, our soil reverts to its original clay, sand, or loam state, or in game parlance it goes back to square one.
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