Master Gardener: Don’t feed your plants, feed your soil

If you’re like most gardeners, I know what you’re thinking; soil doesn’t need the nutrients; the plants do. So how does feeding the soil help our plants?

There is another world below the soil surface that most home gardeners don’t fully understand. Yet soil scientists tell us that in ideal conditions, it is teeming with billions of beneficial microorganisms that provide plants with everything they need to grow and produce naturally. The work done by the roots is critical to the existence of the plants. If the roots are not healthy, there is no way the plant will ever be healthy. One key element to having healthy roots is to put them into a healthy soil. This healthy soil must be established before the plants go into the ground and a healthy soil will meet or exceed the growth requirements of the plants.

Think of it in terms of our own bodies. If you are trying to be as healthy as you can, do you fill up on a bunch of junk food every time you are hungry? Or do you look for something that satisfies your hunger craving but also isn’t loading you body with empty calories? It’s the junk food vs. whole foods argument, but it can be applied to plants, too.

Plants can get their primary nutrients in one of two ways. The first is through manmade synthetic fertilizers. This is typically salt-based compounds which include nutrients such as nitrogen, potassium, or phosphorus. Those chemicals become available to the plant as the particles dissolve, or when they pass by the roots, as with water-soluble fertilizers. This is a proven way to get nutrients into the plant quickly. And it works–very well. But so does junk food to ease your hunger pangs–temporarily. While your plants will respond to the fertilizer, and your taste buds will love the junk food, is that really how you want to take care of your health, or the health of your plants long term? Nutrients that aren’t immediately taken up as they pass by the roots are gone forever. To make matters worse, the excess salt and unused chemicals can pass through to the aquifer, or as runoff into watersheds. Either way, the damage downstream to plants, wildlife, climate and humans can have adverse consequences. True, it would take a lot of salt residue to significantly harm all the living organisms in the surrounding soil, but it does have an adverse effect, especially cumulatively.

That brings us to the second method of delivering nutrients to plants, the alternative to synthetic (junk food) fertilizer. It’s organic matter such as compost and organic fertilizer that builds the lasting health of the soil. If synthetics are junk food, then organic matter is health food… and a good method for building long-term soil quality. In this method, rather than trying to satisfy the immediate craving by supplying a quick fix with no real lasting nutritional value, the focus instead is on giving soil what it needs to naturally provide nutrients that are available to plant roots when needed most.

These organic nutrients must first be broken down and digested by soil organisms, from bacteria and fungi to other soil-dwelling creatures including small insects and earthworms. Collectively, they release nutrients in an organic form that plants can use, while also improving soil structure. Organically derived nutrients bind to soil particles and are far less likely to leech. The net result is nutrients that remain in the soil until utilized by plants, with little risk to plants of burning or dehydration, even in periods of extreme drought or over-application. As we continue to feed the soil with organic matter (through compost, leaf litter, worm castings, food scraps, natural fertilizer, etc.) existing soil organisms utilize these and continue to supply food and nutrients for a soil environment that supports other living organisms and plant life. The result is a thriving, balanced ecosystem. Just the way nature intended.

Whether you buy or make it, compost is the best way to feed the soil. Every article I have read states that compost is the single most important ingredient anyone can add to their garden. Beyond adding life and fertility to the soil, it does so much more. Compost improves soil drainage, yet allows soil to retain sufficient moisture. It helps create the type of soil structure that is critical for nutrients and water to be absorbed, and plant roots to spread. Compost also helps reduce soil erosion and runoff. It protects plants from certain diseases, moderates pH levels, feeds earthworms and other soil-dwelling creatures, supports beneficial microorganisms, is known to be a growth stimulant, and even buffers toxins in the soil. And the best part – You can easily make your own compost for free. All the ingredients you need come from many things you would otherwise throw away from inside and outside your house. How much to apply? Strive for 5% organic matter by weight in your total garden area. As a rule, one-inch worked into the top four to eight inches of soil will get you close and provide excellent results.

When shopping for other organic alternatives to feed your soil, options are often listed primarily by what they are, such as blood or bone meal. Here is a partial listing of the most commonly available organic nutrients:

• Nitrogen: Dried blood, blood meal, cottonseed meal, fish emulsion, seaweed extract

• Phosphorus: Bone meal, rock phosphate

• Potassium: Greensand, sulfate of potash

Somewhere on the package of each, you’ll find the total analysis of nitrogen, phosphorus, or potassium.

All too often, we randomly add fertilizers in our soil while having no idea whether what we’re adding is even necessary. However, it should be noted that just because it’s organic, doesn’t excuse an overuse of certain fertilizers. For example, chicken manure contains high levels of organic nitrogen. But put too much of it within contact of your plant roots before it’s mellowed, and chances are you’ll burn up tender plants.

So what should we be doing to our soils at planting time? I hope that the soils are tested every three or four years to discover what nutrients are needed and to determine what needs to be added.

One more time: feed the soil, and let the soil feed the plants. Make that part of your new gardening routine and you’ll be well on your way to a healthier garden.

Resources: University of MN, University of Iowa, University of Nebraska