THE GREEN THUMB ALMANAC 

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Soils and Mulch

On This Page!

  • Types of Soils
  • In Search of Loamy Soil
  • Potting Mix or Potting Soil?
  • Make Your Own Potting Mix
  • The Benefits of Mulch
  • Types of Mulch
  • Mulch Calculator

Why is soil so important to the gardener?   Because it limits the variety of plants that can be grown there.  The health of any plant begins in the soil.  As a matter of fact, poor soils are one of the most common causes for plant failure.  All plants have evolved to perform well in certain types of soil.  Cactus, for instance, prefer a soil that drains well.  Whereas, aquatic plants prefer a soil that stays moist.  Knowing your plants soil requirements will make you a successful gardener.  


Soil is a living thing.  Soil is not just dirt.  It contains a variety of organisms; fungi, bacteria, protozoans, insects, worms, mammals, and reptiles.  All of these are important in creating soil structure, as well as, the breakdown of organic matter into usable nutrients by the plant.  In simple terms soil must contain nutrients, water and air in order for plants to develop a healthy root system and survive.  Soil varies greatly from one location to another and its ability to grow plants can differ from yard to yard, garden to garden.

Types of Soils

Sand

Sand is the largest of the 3 types of soil particles.  Sandy soils tend to drain well and provide good aeration.  However, it is low in nutrients and organic matter.

Silt

Silt particles are smaller than sand but larger than clay.  It still feels gritty and is powdery when dry and slippery when wet.  It is commonly found in flood plains.

Clay

Clay is the smallest of the 3 types of soil particles.  It is arranged in flat layers that provide very little aeration.  However, it is tops in nutrient value and water holding capacity.

In Search of Loamy Soil

To the gardener, loamy soil is the holy grail.  Loam is the ideal soil for growing crops and many types of plants.  Loam is composed of 40% sand, 40% silt, and 20% clay.  Loam generally is soft and rich and easy to work.  It has more nutrients than sandy soil and drains better than silt or clay.  The good news is that any soil can be turned into loam by adding organic matter.  The addition of any organic matter, leaves, grass clippings, or compost is the key to turning your soil into loam.  Organic matter is broken down by micro-organisms into nutrients for the plant which turns sandy soils into loam.  Because organic matter is made up of large particles of material it increases aeration and drainage in clay soils.  Never add sand to clay to increase drainage...all you'll create are bricks!

Potting Mix or Potting Soil?

You will often hear bagged commercial potting mediums either called "potting mix" or "potting soil."  Although both terms are used interchangeably the term "potting mix" is most correct.  As stated earlier soil is a living thing composed of both micro- and macro-organisms.  "Potting mixes," however, are sterile products which contain no living organisms.  You may also hear them called "soil-less" mixes.  To make it even more confusing, in the UK you will hear these products called 'composts.'  'Compost,' in the United States, is a term which refers to organic 'composted' material which would be used as a soil amendment...not used in pots.  No matter what you call it, make sure that the product you use in containers is light and fluffy.  Never use heavy bagged 'top soil' products in containers as they can harbor disease and insects and do not provide enough aeration and drainage.

Make Your Own Potting Mix

 The following mixes are suggested for growing foliage plants:

  • Two parts peat, one part perlite, one part coarse sand.
  • Two parts peat, one part coarse sand.
  • One part peat, one part coarse sand, one part pine bark.
  • One part peat, one part pine bark, one part perlite.


Cornell foliage plant mix:
½ bushel sphagnum peat moss
¼ bushel vermiculite, No. 2
¼ bushel perlite (medium fine)
8 tbsp. ground dolomitic lime
2 tbsp. superphosphate (20% powdered)
3 tbsp. 10-10-10 fertilizer
1 tbsp. iron sulfate
1 tbsp. potassium nitrate

The Benefits of Mulch

Using an organic mulch such as wood chips around trees and in shrub beds will provide several benefits. A four inch layer of mulch under trees and around shrubs and perennials goes a long way to keep plants alive and healthy.

Mulch helps to regulate soil temperature resulting in less stress on plants between hot,
dry summer days and freezing winter nights. Mulch allows for less and easier weeding of beds. Organic mulches, as they gradually break down, add nutrients to the soil. Mulching around the base of trees also keeps the lawn mower and weed eater from damaging the bark of trees.

Most importantly, mulching reduces water usage. A mulched area under low-water-use trees with dry land shrubs or perennials can reduce water usage by as much as 50 percent from the water needed to maintain a bluegrass lawn.

Mulching mature trees to their drip line is beneficial as well. For a larger-sized tree this may extend a mulch circle outward from the trunk 20 feet or more, greatly reducing the amount of lawn. Having mulch to that point helps retain moisture in the root area.
(Information courtesy of Missouri Mulch)

Types of Mulch

Organic Mulches are those which decompose and which must be replenished.  They include shredded bark, wood chips, leaves and compost mixes.  Each decompose at different rates and, as they do so, replenish soil nutrients.  Cypress and Cedar mulch decompose more slowly than hardwood mulches.  Leaves and compost decompose very quickly, often in one season or less.  Hardwood mulches are now color enhanced and can be found in red, black or brown. 
Inorganic Mulches are those which do not decompose.  They include decorative stone, lava rock, pulverized tire/rubber mulch and geotextile fabrics.  These materials are often used in xeriscapes and in high traffic areas.  They should not be used around trees as the heat reflected from them can kill thin-barked trees.  We do not recommend the use of geotextile fabrics under your wood mulch to prevent weeds.  Weeds can root into the fabric which makes weed removal very difficult.

How Much Do You Need?

(3 cubic foot bag)

Covers 36 square feet 1" deep

Covers 18 square feet 2" deep

Covers 12 square feet 3" deep

Covers 9 square feet 4" deep

 

(1.5 cubic foot bag)

Covers 72 square feet 1/4" deep
Covers 36 square feet 1/2" deep
Covers 18 square feet 1" deep
Covers 9 square feet 2" deep
Covers 6 square feet 3" deep
Covers 4.5 square feet 4" deep
 
(1 cubic foot bag)
Covers 12 square feet 1" deep
Covers 6 square feet 2" deep
Covers 4 square feet 3" deep
Covers 3 square feet 4" deep
 
(1 cubic yard)
Covers 1296 square feet 1/4" deep
Covers 648 square feet 1/2" deep
Covers 324 square feet 1" deep
Covers 162 square feet 2" deep
Covers 108 square feet 3" deep
Covers 81 square feet 4" deep

Use our handy mulch calculator to determine how much mulch you will need!

Amending Soil  Cotton Bur Compost (2 cubic foot bag)

Amending Clay Soil: 4 bags for every 100 square feet (mix in).

New Landscape Beds: Mix 2 bags for every 1 cubic yard of topsoil.

Peat Moss

1- 3.8 cubic foot bale covers 50 square feet 1" deep (mix in).

1 - 3.8 cubic foot bale covers 100 square feet 1/2" deep (mix in).

One square yard = 9 square feet.

One cubic yard = 27 cubic feet.