Practice No. 14 Replenishing Organic Matter

Practice No. 14. Replenishing Organic Matter

Feeding Plants

Many people think they should feed the plants. There are concerns and considerations with this idea. Plants aren't like people in this regard. How do plants take in nutrients? What nutrients do they need? Are all plant nutrient needs the same?

People do feed plants and plants can directly uptake nutrients. With hydroponic gardening, plants are fed using the Nutrient Film Technique, where all the nutrients a plant needs are included in shallow water, little more than the thickness of film. In regular soil-based gardening, one of the problems with direct nutrient feeding by applying chemical fertilizers is that gardeners don't continually and consistently apply all the nutrients needed by the plants. Fertilizing is done once, maybe twice a year. With certain chemicals, such as nitrogen, if they are not absorbed or used, they are leached out of the root zone and wasted (which sometimes causes pollution). Other chemicals applied but not used by the plant may build up in the soil causing an imbalance. These imbalances then retard or inhibit the plant from their uptake. Most chemical fertilizers applied to the soil are salt based, creating a harmful buildup in the soil over time, killing beneficial microbes and destroying soil structure.

What is a gardener to do? To apply a steady supply of nitrogen, the gardener would need to be testing the soil and plant weekly. Having the plant and soil tested for each feeding is not feasible. Is there a general, all purpose, broad based, low maintenance way to provide nutrients to plants?

The low maintenance, ecologically-friendly method is to feed the soil, or specifically, the microbes in the soil. Beneficial microbes breakdown organic matter, containing carbon atoms, to forms usable by the plant. The addition and incorporation of organic matter and composted organic matter is a non-technical solution that fosters a very complex system called the soil food web. This is the below ground technique outlined in Practice No. 3.

What to Use

Because organic matter is broken down by the microbes and used by plants, it needs to be replenished. Basically, the higher the water needs of plants, the higher the plants' nutrient needs. Low water-use plants require less organic soil amending and replenishing than high or medium water-use plants. Composted plant and animal products are the best natural organic sources, not just for initial soil amending, but for replenishing. When replenishing with compost, topdress with a half inch to an inch layer in spring and or fall, depending on the plants' needs. Compost can either be home made or purchased.

Composted cottonseed meal, alfalfa pellets and meal, corn meal and corn gluten meal, dry horticultural molasses, worm castings, bat guano, fish emulsion, fish meal, kelp meal, bone and blood meal are some other carbon based products normally used to replenish organic matter in the soil, or broadcast on top of the soil for replenishing.

Follow the directions on the bag for correct application. Compost is usually added to the soil in “inches thick”, all the rest is applied according to pounds per 100 or 1000 square feet.

As a general rule, non-composted organic matter such as cottonseed, alfalfa, feather, kelp, fish, and bone meal, guano and earthworm castings, etc. are added at a rate of 10-20 pounds per 1000 sq. ft. Apply these organics two to three times a year – late winter or early spring, early summer and fall, depending on the plants' nutrient needs. If the soil is deficient in minerals, greensand, rock dust, rock phosphate, rock powders such as lava sand, basalt and other volcanic materials can be added at the rate of 20 – 80 pounds per 1000/sq. ft. annually.

I've used an organic amendment with the trade name Yum-Yum Mix®, but you can mix your own using a variety of organic materials. Yum-Yum Mix® is a blend of cottonseed and kelp meal, greensand, rock dust, rock phosphate, humate and dry molasses. I have added a small handful in the planting hole for 2” - quart size plants for years and have great success (add larger quantities when planting larger plants), and sprinkle it over my xeric beds each spring.

Fine Tuning

Trees, shrubs and most perennials prefer fungal dominated compost, while most annuals – flowers and vegetables-- and grasses – turf grasses included – prefer bacterial dominated compost. Fungal dominated compost contains a higher percentage of brown organic material, higher in carbon, C (higher C:N ratio). Bacterial dominated compost contains a higher percentage of green organic matter, higher in nitrogen, N (a lower C:N ratio). Refer to Practice No. 13 on making compost and compost teas that are either fungal or bacterial dominate.

Foliar Sprays

Organic foliar treatments may be used and are helpful. Foliar applications are helpful in stimulating the natural defenses of plants, “as a means of supplying supplemental doses of minor and major nutrients, plant hormones, stimulants, and other beneficial substances. Observed effects of foliar fertilization have included yield increases, resistance to diseases and insect pests, improved drought tolerance, and enhanced crop quality. Plant response is dependent on species, fertilizer form, concentration, and frequency of application, as well as the stage of plant growth.” (Foliar Fertilization, by George Kuepper, The National Sustainable Agriculture Information Network, ATTRA,

Typical foliar sprays are liquid seaweed, liquid fish meal, liquid horticultural molasses, liquid humate, liquid compost tea or aerobically activated compost tea (AACT). Applying organic foliar sprays when the plant or landscape is stressed due to heat, drought and especially hail is a boost to the plant. Foliar sprays are not a substitute for the incorporation of organic matter into the soil.

Some points to keep in mind when using organic foliar sprays:

  • Insure your sprayer is clean and free from chemical or disease contaminants.
  • When applying beneficial microbes, do not use chlorinated water.
  • The best results are achieved when using finely atomized particles of water and spray.
  • Most of the plant's stomates are located on the undersides of leaves. Therefore, spraying the undersides of leaves is important for increased absorption.
  • Spray when wind is minimal, at temperatures below 80°, in early morning or in the evening, and when humidity is higher than average.
  • Include a surfactant to the solution to decrease leaf surface tension.

Weed and Feed

I don't recommend the application of weed and feeds, unless it is corn gluten meal at a rate of 20# per 1000 sq. t. “Corn gluten meal works by inhibiting the root formation of germinating plants. It generally does not inhibit the roots of mature plants or transplants until your reach very high rates (80 pounds/1000 ft2 or higher). It should be applied before germination of the weeds. The weed will germinate and usually forms a shoot, but does not form a root. After germination, a short drying period is needed to kill the plants that have germinated but have not formed a root. Timing is critical. If it is too wet during germination, the plants will recover and form a root. (This is also true of chemical preemergence herbicides). It is preemergence only, there is no postemergence effect on established weeds. In fact, it makes a great fertilizer for germinated weeds” (Dr. Nick Christians, Iowa State University, “How to Use Corn Gluten Meal”). Dr. Christians also cautions to be sure you are getting real corn gluten meal. Some feed suppliers and garden stores have been substituting corn gluten feed and distillers grain.

Regular weed and feeds typically sold are chemical salt-based fertilizers with an herbicide. Many people have damaged shrubs and trees with indiscriminate use of herbicides in this manner.