Basic Soil Amendments

In this chapter of the JR Johnson Supply catalog, we’re beginning with the descriptions of some common soil amendments. This may seem a bit basic for many of you, but some of you may be just starting out and these descriptions could be very helpful when it comes time to decide what you need for specific crops or situations.

Additionally, there are those of you who may wish to mix your own soils, and knowledge about characteristics of these amendments can be indispensable. You will find that some amendments hold water quite well, while others can improve drainage; some may help to adjust soil pH while others may have no effect; still, there are others that serve to loosen a mix which could otherwise be quite heavy. It is important for you to be aware of these basics as you plan your growing strategies. We hope these descriptions will help.  

Peat Moss

Peats are formed by the accumulation of specific plant materials in poorly drained locations. The value of a peat depends on the type of plant material and its degree of decomposition.

Sphagnum peat is the result of partially decomposing sphagnum moss leaves and stems. When compressed, it exhibits sponginess and elasticity. Sphagnum moss has the highest water-holding capacity of all the peats, and will retain this quality after being air-dried.

Sphagnum peat won’t change chemically or biologically during steam sterilization. Its value is in its ability to improve soil aeration and increase drainage to promote plant root development. It is used throughout the greenhouse trade for vegetable and plant production, mushroom production and mixing your own growing media. It is widely used for bedding flat production, and for larger pot and hanging basket production.

Sphagnum peat is available in two grades: horticultural (grower grade), and special coarse (chunky). Horticultural grade sphagnum peat is made up of pieces ranging from pea-size to thumbsize. Special coarse contains very coarse pieces ranging from thumb size to fistsize. The special course is often used as a mulch in rose beds, although some growers prefer it as a potting medium for azaleas.

Peat moss is packed in tight, compact bales under hydraulic pressure. All bales are polyethylene lined so as to enable outdoor storage, if required. The peat moss is clean, and contains no foreign material. Its low acidity of 3.5 – 4.0 makes it inhospitable to most insects and disease. The standard 3.8 cubic foot compressed bale measures 20.5 x 17.1 x 15.4 inches, and expands to about 7-8 feet (fluffed). Average bale weight is 57 lb.

When used as an amendment in soil media, peat is mixed with other amendments such as perlite, vermiculite, composted bark or rock wool. Because of the low acidity of peat, the pH of these mixes needs to be adjusted by adding lime.  

Vermiculite

Vermiculite is a mica-type material which is mined as an ore, and is then heated to above 1400 degrees. This heating causes the accordion-like particles to expand, making them capable of holding large amounts of plant available air, water and nutrients. Heating also makes vermiculite sterile. Vermiculite has a high water holding capacity, good buffering characteristics and adequate cation exchange capacity. It has an absorptive capacity for fertilizer. It contains by nature, amounts of potassium, magnesium and calcium. These elements are available as a slow-release supply.

Vermiculite is available in two sizes, which all perform well horticulturally. The medium size tends to hold more moisture. It is commonly used for covering seed in propagation situations.  

Perlite

Perlite is a white, crumbly volcanic mineral which is mined and then heated to 1800 degrees. This heating causes the particles to expand, which makes them porous. These particles provide excellent drainage, by trapping air and water on their irregular surfaces. Perlite will hold 3-4 times its weight in water. It is neutral in reaction and has no nutrient content, buffering action, or cation exchange capacity. The particles are sterile and have a pH of 6.0 to 8.0. It is double screened, for the reduction of dust particles. Perlite is available in coarse and medium grades.  

Horticultural Rock Wool

Rock wool fibers are produced by spinning or blowing molten basalt rock. These sterile, inert fibers will not burn, rot or absorb moisture or odors. Rock wool holds water at 90% porosity, keeping more water available for plant uptake. It wets up quickly and evenly, and has good ion exchange. This precise water holding capacity lets you reduce watering frequency and associated labor costs. Rock wool is ideal for propagation and soil conditioning.

The addition of just 25% rock wool to a variety of soils, composts and peats can increase air-filled porosity by as much as four-fold.  

Coir

Coir is a natural and renewable planting media made from 100% renewable and natural coconut fibers. During coconut harvest, the tough husk of the coconut is removed and soaked in fresh water and, after a period of time, the pectins, which bind the strands together, begin to break down. The nut is used for food and the long fibers for sailor’s ropes, leaving behind the short fibers and the dust, or as it is called in that industry, “coconut coir pith”. This remaining coconut coir pith is stacked “mountain high” and allowed to naturally decompose. With the help of modern technology, the decomposed coir pith fibers are heat-treated and then compressed into the easy-to-handle bricks, blocks or loosely compressed bale forms. In the horticulture market, it is known under the brand name of “COIR.”