Growing Medium

Types of Organic MediaA – Sphagnum Peat Moss

1 – the remains of dead plant materials harvested from peat bogs

2 – 1/25th of an inch of compressed moss equals one year of growth

3 – Most is imported from Canada. (only 5% of worlds supply is in the U.S.)

4 – very high water holding capacity makes it important for horticultural usea – weighs 6 ½ lbs. per cu. ft. when dryb – weighs approx. 100 lbs when

saturatedc – can hold 15 to 20 times their

weight in water5 – very high in pore space

B – Sawdust

1 – replacing peat in some areas

2 – certain trees contain harmful substances (walnut and ceder)

3 – bacteria that decompose sawdust rob the soil of nitrogen

C – Sand

1 – deep-mined white mountain sands are mainly silica

2 – free of diseases, seeds, and insects

3 – increases porosity

D – Perlite

1 – volcanic rock mined as an ore2 – heated particles expand like popcorn3 – pH of 7.0 to 7.54 – improved aeration and drainage5 – is dusty and does float

E – Vermiculite

1 – Mica-type mineral expanded by heating

2 – flat plate-like mineral expands like an accordion but can be destroyed

3 – holds 500% water by weight

4 – high in potassium, magnesium, and calcium

F – Coconut Coir

1 – made of the outside shell from coconuts

2 – increases aeration and drainage

II – Composition of the Growing MediaA – Solid material

1 – approx. 50%2 – organic or inorganic depending on soil type

B – Liquid

1 – approx. 25%2 – too much water and plants become “water-

logged”, causing fungus or fertility problems

C – Air space

1 – approx. 25%2 – too much and soils cannot hold water

3 – too little causes restriction to rooting

III – Advantages of Soil-less Media over topsoil A – consists of material with known properties

B – typically more consistent

C – easier to handle and mix

D – fertilizers and pH can be adjusted to desired levels

E – correct drainage and water-holding capacity are adjusted

F – sterilization is generally not required

G – cheaper to prepare

IV – Soil Moisture A – Three forms of water

1 - Gravitational Water – temporary and drains from a soil by gravity

2 – Hygroscopic Water – mostly in vapor form and unavailable to plants

3 – Capillary Water – water held between soil particles by capillary action

B – Field Capacity – the amount of capillary water that is available to plants after gravitational water has drained

C – Wilting Point – the amount of water present when plant starts to wilt; soil particles typically hold water with 15 atmospheric bars of pressure