Organic vs. Synthetic Fertilizer

For as long as I can remember, gardeners have been at odds regarding the use of organic versus synthetic (inorganic) fertilizers.  As a gardener, of course the choice is yours alone. Both provide NPK but differ in their structure, use and impact on the soil and plants. I like to use both; organic such as compost in vegetable, herb and perennial beds and a mix of organically amended soilless media and synthetic in containers (hanging basket, planters and window boxes). If you are a new gardener looking for information on this topic, please read on, as there are advantages and disadvantages to both.

What is Organic Fertilizer / Soil Amendments

Organic fertilizer is derived from natural sources and contains NPK.  These natural sources include blood meal, bone meal, kelp, compost, rock minerals, earthworm castings and manures. Some organics such as kelp are also available in a concentrated liquid form and are mixed with water before application. Manures used are cow, sheep, horse and mushroom. Homemade manure or earthworm casting tea is also popular with gardeners. Manures must be very well aged before application and are available from garden centres in a bagged form; ready to use.

Organic fertilizers/soil amendments are usually used in vegetable and herb gardens, perennial, annual and shrub beds. They are more expensive than synthetic and involve more physical work on your part to mix with garden soils.

Organic fertilizer is not available immediately to the plants unless you are using the water soluble concentrated liquid forms.  Microbes in the soil must break down some of the organic compounds before they become available in nutrient form to the plants. This takes time but the result is a more nutrient enriched soil.

Information on the amount of nutrients in organic fertilizer such as manure is not always readily available. This is usually not a big concern for the average home gardener as the NPK ratios for organics are quite low.

Over fertilization is less likely when using organics. Organics gradually release nutrients causing less stress on the plants. But overdoing it can happen. For example, using fresh manure in your garden beds. Fresh manure can burn tender plant roots and cause plant death.

Organic matter has an added benefit; it improves soil structure, the health of the soil and its microbes, water holding capacity and soil permeability. To be effective year after year, organic fertilizers/ soil amendments must be applied at least once per year in early spring as plant growth begins. They can also be added to vegetable gardens and flower beds before winter as ground frost helps to break up the soil and amendment particles.

Organic fertilizers are environmentally friendly. They have low salt concentrations which encourages earthworm and healthy microbe activity.

Synthetic Fertilizers

Synthetic fertilizers are made by man, inorganic (non –living sources) and manufactured from chemicals. They include NPK, other nutrients and micronutrients. Synthetic fertilizers are best used for maintaining hanging baskets, window boxes and container plantings. They do not benefit the soil itself as organics do.

Synthetics are available in powdered form, concentrated liquid, slow release pellets and hard spikes. Powdered and concentrated liquid fertilizers must be mixed with water and applied routinely through the growing season. The benefits do not last long unless you use the spikes or slow–release pellets. Synthetic fertilizers can leach quickly, depleting the soils natural nutrients.

Water soluble synthetic fertilizers act quickly; and are directly available to the roots for absorption. Example: Miracle Grow 20-20-20 is a synthetic water soluble fertilizer. It comes in a concentrated granular form that must be mixed with water. There are many different formulations of synthetic fertilizers allowing for more precise fertilizer ratios that fulfill specific growing requirements.

Soilless media and synthetic fertilizers are often used in greenhouses for growing container grown plants or bedding out flats. Soilless mixes are usually made up of perlite, peat moss, vermiculite, coir and contain zero nutrient value. They do not contain any soil so are free of pathogens that can negatively affect a greenhouse crop. This allows the grower to control all aspects of the growth of his greenhouse crops such as hanging baskets, window boxes and containers/planters.

Please be aware that the rapid growth of many plants in these containers will quickly use up the nutrients. At home, this lack of nutrients is exacerbated by daily watering which flushes out a lot of the nutrients. This is why you must fertilize containers on a regular basis.

It is very important to mix and apply synthetic fertilizers as directed.  Using too much is not good. This is also true of synthetic lawn fertilizers. Highly concentrated synthetic mixes can negatively affect soil pH and contribute to a buildup of toxic soluble salts in the soil.  Synthetics used to excess can also cause root burn, stunting of growth, plant death and run-off into bodies of water that can harm animals, birds and fish.