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Are fertilizers just junk food for plants?

The fertilizers that fuel plant growth on today's farms also weaken their natural ability to stave off disease, heal from injuries, and fend off pests and pathogens.

Everyone understands the folly of relying on junk food to provide any kind of lasting nourishment. The empty calories in added sugars and certain types of fats might fill us up fast, but they don't supply the nutrients we need, leaving us ill-equipped to tackle life with all the energy and vitality it requires of us.

As it turns out, a similar problem plagues plants that have been fed a steady diet of conventional fertilizers.

According to recent research, fertilizers containing the magic triad of ingredients nitrogen (N), phosphorous (P) and potassium (K) may make plants grow bigger and faster, but they also cause plants to shut down the delicate, nutrient-generating give-and-take relationships that exist in the root microbiome (called the rhizosphere).

The result? Couch-potato plants that look pretty on the outside, but are low in minerals and nutrients on the inside.

In a piece for Nautilus titled Junk Food is Bad for Plants, Too, Anne Biklé and David R. Montgomery write:

"The things that fuel plant growth on today’s farms, chiefly NPK fertilizers, are not the same things that plants need to stave off disease, heal from injuries, and fend off pests and pathogens ... Long before agrochemical companies existed, the botanical world relied on the phytochemicals it churned out to remain healthy. Couple their internal chemical factories with cultivating a root microbiome and you have the secret weapon that helped plants conquer the continents over the past 450 million years. Tinkering with these time-tested and co-evolved arrangements, however, can turn plants into botanical slackers."

This decline in plants' nutritional value is far from negligible: a 2009 study of nutrient levels in U.S. crops indicates a 5-40% overall decline in the nutrient content of fruits and vegetables over the previous 50-70 years.

Just how does the root microbiome work?

So what is it about the rhizosphere that's so essential to not only a plant's health, but its nutrient content, too?

It all comes down to understanding the underground economy. When not being helped along by NPK fertilizers, plants use their energy to produce and hand out "nutritional goodies" to the billions of beneficial bacteria, fungi and other microbes living in the soil—think of it as a free lunch. In return, these microbes deliver metabolites, minerals, nutrients and other beneficial compounds to a plant's roots, including a naturally-produced version of the NPK triad that stimulates growth. This symbiotic relationship, along with exposure to pathogens and pests, also encourages plants to produce phytochemicals (like polyphenols, which play a role in the prevention of degenerative diseases). 

In short: Plants that haven't been raised on a steady diet of conventional fertilizers are going to give you a whole lot more bang for your nutritional buck. And, they're going to be hardier when it comes to fighting off natural challenges in the growing cycle.

Raising crops on a junk-food diet? All that does is transform the soil and root system from a "vital, two-way trade zone to one-way straws sucking up fertilizers," as Biklé and Montgomery put it.

Nourishing your garden naturally

The solution isn't to leave plants to fend for themselves, but rather to make sure you're feeding the soil in addition to the plant in order to restore a healthy and balanced rhizosphere.

"Creating a living soil rich in humus and nutrients is the key to growing great fruits and vegetables, abundant flowers, and long-lived ornamental trees and shrubs," explain the experienced staff members at Rodale's Organic Life. "The overall fertility and viability of the soil, rather than the application of fertilizers as quick fixes, is at the very heart of organic gardening."

If you're not already using organic fertilizers to keep your garden healthy and happy, now's a great time to get both your plants and your soil back into fighting shape. Organic fertilizers are made from natural plant and animal materials and/or mined rock minerals. Look for products labeled  “slow release” and “low analysis,” and steer clear of products that have an NPK ratio that adds up to over 15. When in doubt, ask a trusted garden center owner to recommend fertilizer brands that meet organic soil-nourishing standards.

How do you feed your garden soil? Do you purchase organic fertilizers or create your own?


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