chapter 8: soil and media management (horticulture)

soil

decomposed rock/minerals (parent material), comprised of layers

Organic soils

>20% organic matter (OM), Small percentage of soils, but very productive, Often called peat or muck soils

Mineral Soils

<20% organic matter

Sandy Soils

excessively well drained, subject to drought, needs frequent irrigation, subject to nutrient leaching, low in organic matter

sandy loam

mostly sand, but enough silt and clay to hold water and nutrients, warm quickly, works great for veggies and fruits

loam soils

mellow soils, balance of all the characteristics, preferred soil types

silt loam soils

>50% silt, smooth like flour, usually profitable soils

clay

poorly aerated, poorly drained, easily compacted, “lighter” soils are preferred

bulk density

mass per unit volume of soil, tells the amounts of pores, used to determine if a soil can be used in a container mix

field capacity

maximum amount of water that can be held against gravity

structure

arrangement of particles into groups called peds, essential for aeration and drainage, destroyed by over-tillage or tillage when soil is too wet, organic matter helps improve structure

Soil Reaction (pH)

Affects nutrient availability, ideal is slightly acidic (6.2 - 6.8)

Common soilless media components

Peat Moss, Bark, Coconut coir, Sawdust, Whole tree chips, Animal manure composts, Crop by-product, Composted municipal garbage-trash, Perlite, Vermiculite, Calcined Clay, Sand, Rock Wool, Rice hulls

Peat Moss

• Organic (mined from bogs)

• Very common

• High CEC (holds a lot of nutrients)

• Great water-holding capacity 

• Good aeration

• Not completely sustainable

• Low pH for most plants (approx 4.0)

• Hard to re-wet once dry

Bark

• Organic

• Redwood, fir and pine bark are common

• Hardwood bark can be used

  • Watch out for secondary compounds

• Less expensive than peat

• ALL bark should be composted and screened

Coconut Coir

• Organic (made from coconut husks)

• Less common

• Cheaper than peat, but similar characteristics 

• Once dry, very difficult to re-wet

  • Soaking may help

• Often very salty - must be leached before using

Sawdust

• Organic (waste)

• May be cheaper than peat

• Composted is best

• High C:N ratio - watch out for N tieup

Whole tree chips

• Fresh pine chips work well in nursery containers

• Mixes of chips with peat may work in green houses

• Animal manure composts

• Should be composted to:

  • Reduce disease pressure

  • Deplete weeds seeds

  • Reducted C:N ration  (carbon and nitrogen)

  • Stabilize mixture 

• Test first, use with cation

Crop by-product

• Straw, peanut hulls, bagasse (sugarcane fiber) and other crop wastes can be used

• Watch out for diseases

• Watch C:N ratio

• Composted municipal garbage-trash

• Kitchen waste and solid trash can be composted and used

  • Highly variable

• Landscape waste mixed in helps, but C:N ratio is large

• Perlite

• Made from volcanic rock that’s been heated until it puffs up

• Very common

• Nearly inert (very little CEC)

• Generally added to decrease weight and increase aeration

• Vermiculite

• Made from micas (minerals made up of thin sheets) that are heard until they expand

• Less common

• Holds more water than perlite

• Has greater CEC than perlite

Calcined Clay

• Clay particles are baked to harden them

• Used for drainage/aeration

• Good structure

Sand

• Course - helps with drainage/aeration

• Adds weight

• Watch out for salt

• Too heavy for most potted crops

• Rock Wool

• Mineral (made by melting rocks and spinning the molten material into fibers (could irritate skin)

• Inert

• More common in hydroponic systems

  • Can be used in soilless media

• Disposal/recycling is problematic

• Rice hulls

• Organic (par-boiled rice hulls)

• Cheaper than perlite or vermiculite

• Renewable

• Light and easy to ship