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Pros and cons of organic vs. synthetic fertilizers

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Pros and cons of organic vs. synthetic fertilizers

Bags of commercial compost on top of a pile of homemade compost in New Market, Va. Another growing season is fast approaching, and before you can seed you must feed. Now is the time to decide wheth...

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POSTED March 19, 2011 2:06 a.m.
Another growing season is fast approaching, and before you can seed you must feed.

Now is the time to decide whether to use organic or synthetic fertilizers to enrich the soil. They produce similar results but come at it from different directions.

Most organic fertilizers are derived from plants and animals. This group includes manure, bone and blood meal, seaweed, compost and minerals. All are rich in nutrients, but must be “cured” or broken down by bacteria before they can nurture plants and condition soils.

Synthetic fertilizers are commercially produced from petroleum or natural gas, and are packaged in easy-to-apply granular or liquid forms. They give plants a vigorous although short-term jolt.

“Plants don’t know the difference if you’re using a synthetic or an organic. It’s all chemical to them,” said Valerie Locher, a horticulturist and landscape manager from Housatonic, Mass. “But the beauty of organics is that they’re naturally slow-release. They’re there for the entire season.”

Locher uses synthetic fertilizers when planting flowers in containers. “I plant a lot of annuals so I want their growth to be really quick,” she said. “Synthetics leach into the soil with the first watering. Instant nourishment.”

Organic fertilizers may not be the answer if:

— You don’t like odors. “Fermented seaweed and fish make beautiful fertilizers but they’re often difficult to use because they smell,” Locher said. “If you’re spreading something like minerals on the ground, there’s no odor problem.”

— You want to reduce your workload. “If it’s a compacted soil and you have a hard time breaking ground, then it will be hard for any roots to grow,” Locher said. “That means you’ll have to do a lot of soil work in the spring — I call it ‘fluffing’ — to mix your nutrition deep into the ground.” Synthetics are easier in this case because they can be broadcast over the surface of the ground. The granules or liquids seep into the soil as soon as water is applied.

• You’re looking for consistency. Synthetic fertilizers are sold with a three-digit chemical code displayed on each bag. If the label reads “10-10-10,” it’s a blend of 10 percent nitrogen, 10 percent phosphorous and 10 percent potassium by weight. (What’s left is filler, usually sand or limestone.)

But organic fertilizers, especially the kitchen composts or farmyard manures, are variable mixtures. An all-purpose, 4-6-2 load when supplied one year may test out as an acidic 4-3-6 application when delivered the next.

Organics, however, do provide benefits you won’t get from the synthetics.

Organic fertilizers:

•Build up the soil structure, boosting its water-holding capacity, and adding to its biodiversity and long-term productivity.

• Improve drainage, minimizing soil erosion and soluble nitrogen- and phosphorus-rich runoff.

You don’t have to be an organic gardener to use organic fertilizers. It may just be practical. Many can be obtained in bulk for little or no cost from nearby livestock operations, municipal green-waste collection centers and dump sites, said Richard Koenig, a soil scientist at Washington State University.

“Recycling makes use of materials that otherwise would go to a landfill,” Koenig said. “You can get hung up too much about what makes a fertilizer. Basically, anything organic can be used directly or indirectly in the soil.”
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