Mother Earth Living

How to Feed Your Soil

The Backyard Gardener (Lyons Press, 2017), by Kelly Orzel, is a concentrated guide to sustainable gardening, whether in a backyard or on a large farm. Orzel is a master gardener and horticulturist who shares her academic and farming experience as an author and freelance writer. The following excerpt discusses what you can add to your soil to keep it healthy.

All living things need to be fed; the more nutrition an organism has, the more productive it is. Therefore, you want to enrich the soil such that both fertility and moisture retention increase. Compost is the ideal amendment, full of just the right amount of macro- and micronutrients. Leaf mold and cow, or farm animal, manure are also excellent soil conditioners. Develop your own stash of leaf mold by collecting and wetting leaves in either black plastic bags or wire cages for up to two years. Farm manure must be aged, well-rotted, or composted, as the nitrogen is not available in the first year. Nutrients, specifically nitrogen, must be converted into a form that plants can absorb, a process called mineralization. If the nitrogen isn’t broken down, the manure has a good chance of burning plants’ roots or foliage due to the high ammonia content. Mulch and other organic bulky materials suppress weeds and encourage earthworms and other beneficial microbes to tunnel to the surface to reach the new organic matter, thereby improving drainage, aeration, and soil structure.

I often hear gardeners talk about fertilizer as if it’s a dirty word. You wouldn’t expect to go through life without eating foods containing vitamins and minerals, so why would you deprive your garden of such nutrients — especially if they’re from natural sources? Plants, particularly flowering ones, need to replenish spent or lost minerals, but as with any vitamin regimen, the right balance is critical. This is why soil tests are so important. Macronutrients are three of the seventeen essential minerals that plants need in large quantities for optimum growth, and include nitrogen (N), phosphorus (P), and potassium (K), often referred to as NPK. Nitrogen is needed to synthesize amino acids, chlorophyll (particularly important for photosynthesis), enzymes, nucleic acids, and proteins, and responsible for lush, leafy green growth in plants. Phosphorus plays a vital role in strong root and stem development. It’s integral to several crucial biochemical reactions such as photosynthesis, respiration, and energy storage and transfer that are necessary for all plants’ normal life cycles. Potassium is important for many processes, including drought tolerance, water retention, and other regulatory functions, but is well-known for its critical part in bud and flower formation. Potash (K2O), nitrate of potash (KNO3), and sulfate of potash (K2SO4) are all good natural sources of potassium. Calcium (Ca), magnesium (Mg), and sulfur (S) are considered secondary nutrients, and you should pay attention to these levels on your soil test results. Trace, or micro-, nutrients like boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn) are essential, but are required in smaller amounts. The remaining elements, hydrogen (H), carbon (C), and oxygen (O), are considered non-fertilizer minerals and are delivered through air and water.

Fertilizers are differentiated by varying amounts of nutrients, particularly macronutrients. This is clearly delineated by the three numbers listed on the packaging, each indicating the percentage of nutrients. These ratios are often referred to as NPK for their respective amounts of nitrogren, phosphorus, and potassium. So a 20-10-15 package is made of 20 percent nitrogen, 10 percent phosphorus, and 15 percent potassium. The remaining 55 percent of the bag is usually inert filler material. Balanced fertilizers, such as 10-10-10, have equal amounts of these macronutrients and are good general purpose choices for later in the season. Organic fertilizer options are often bulky, sloppy, smelly, and take time to work in your soil, but they provide natural, specialized amendments for your garden. Check out some of my favorites below:

Blood meal (12-0-0) is a highly concentrated nitrogen amendment, good for leafy vegetables and to replenish the soil after hungry brassicas have depleted the nutrient stores. Made of dried animal blood (typically cow), it is a powder that can be applied to the soil and worked in or dissolved in water or a liquid fertilizer. Since it quickly adds nitrogen to the soil, follow the instructions as the excessive ammonia can burn your plants if it’s not used properly. Also be sure to bury it well as its smell can attract some unwanted critters like dogs, possums, raccoons, and other meat-eating animals. Alternatively, blood meal can be a deterrent for herbivores like deer, moles, and squirrels.

Bone meal (3-15-0), made of ground -up animal bones, is a well-known source of phosphorus. This fertilizer slowly releases its nutrient over time, and as such, I apply it to the hole directly at planting before my transplants or tubers are set in so my flowers and fruiting vegetable will have a reliable supply by the time they bud up. 

Fish emulsion (5-2-2) is my favorite amendment, and I use it often. Derived from fish waste, it supplies a gentle dose of nitrogen with additional phosphorus, potassium, and other trace nutrients. I dilute it according to the directions and apply it to my crops at transplant and every few weeks afterward. Its foul smell is infamous, but it’s well worth the effort of holding your breath!

Kelp meal, or seaweed, can be applied as mulch, in liquid or granular form. Obviously an ocean product, it is an excellent source of trace minerals rather than macronutrients. Liquid kelp has higher levels of valuable growth hormones than powdered or mulched forms. Many times you may even find fish emulsion and seaweed blends at the store, which provide the best of both worlds — the fish supplies your NPK and the kelp everything else!

Other meals like alfalfa, corn gluten, cottonseed, feather, and soybean meals are agricultural byproducts and available in granular or pellet form. They are wonderful sources of organic nitrogen as well as trace amounts of other nutrients, but be sure that you are purchasing organic varieties as those not labeled as organic may have been treated with pesticides.

Potash, the byproduct of burning wood, is high in potassium. So simply recycle your non-treated wood ash into the garden for your fruiting vegetables, being careful not to over-apply. As with any fertilizer, organic or not, too much of a good thing can cause imbalances that will do more harm than good. It is best to apply one-quarter to one-half pound of potash per one hundred square feet in the spring or fall so it has adequate time to be worked into the soil.

Lime applications are used in acidic soil to raise the pH to the optimal 6.5/7.0. Remember, if your soil is too acidic or too alkaline, it will lock up the nutrients. To ensure mineral availability perform a soil test and apply if needed. As a bonus, lime also contains calcium and sometimes magnesium. If your soil test shows an additional need for magnesium, select dolomitic lime.

Sulfur does the opposite of lime — it decreases your soils pH. If your soil is alkaline, it can bring the pH down to increase nutrient availability or create ideal conditions for acid-loving plants like blueberries, strawberries, and azaleas.

Rock phosphate is just what its name suggests — it is naturally occurring rock that is high in phosphorus, as well as a few micronutrients. Again, this is a slow-release amendment and thus needs to be added at time of planting or before in order to be effective.

You don’t need to be a vermiculturist to have earthworm castings. You can build your own bin or buy the castings in a catalog and toss them into the soil. This biological batter is essentially worm poo — yes, you heard correctly — worm poo. It not only improves your soil structure, but is full of essential nutrients that are immediately available to your plants. Worm castings are a completely natural, organic fertilizer that can’t burn your plants and add nothing but goodness to your soil!

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Reprinted with permission from The Backyard Gardenerby Kelly Orzel and published by Lyons Press, 2017.

  • Published on Jul 18, 2018
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