Compost Vs. Fertilizer

Compost and fertilizer both add nutrients to the soil that help plants grow in the short-term. However, compost is a kind of sped-up version of what happens in nature: Organic matter such as leaves, manure and other debris fall to the ground and are broken down into soil and food by microorganisms. Fertilizer packs more of a macronutrient "punch."

Fertilizer provides macronutrients such as nitrogen, potassium and phosphorus. It may also provide micronutrients, or trace nutrients such as calcium, magnesium or sulphur. Fertilizers produced for sale contain measurable amounts of each macro- and micronutrient, allowing growers or researchers to monitor plant needs accurately. Fertilizer also tends to have a strong concentration of these nutrients to add to depleted soils.

Although fertilizer adds nutrients to the soil, it is not a balanced addition of nutrients. Microorganisms in the soil react to the influx of nutrients first, i.e., they eat first. So when the soil is suddenly inundated with nutrients, the plants do get some of the nutrients, but meanwhile the microorganisms use up all the other available micro- and macronutrients in the soil because they suddenly have so much of a nutrient that was unavailable before. This depletes a huge range of nutrients in the soil each time fertilizer is used. Overfertilizing also harms plants, causes leeching into underground water reservoirs or washes into surface fresh water supplies.

Compost is a balanced, structured soil amendment. The microorganisms in compost have already reached a kind of equilibrium. The rich assortment of beneficial organisms in the compost are now primed to quickly turn any fallen organic matter into food for your plants, and there is no danger of harming your plants so long as you use finished compost, or compost that has decomposed until it is humus. The soil structure is primed to hold a balance of moisture (instead of soaking or bone-dry), and will slowly release nutrients over time.

While compost does not have as high a concentration of macronutrients, this is actually better for plants and the soil in the long run. Constantly spiking your plants with fertilizer is about as healthy as feeding people sugar. While fertilizer provides energy for your plants, the new growth is weaker and more susceptible to insect and weather damage than slower, stronger growing plants feeding from a balanced meal of compost.