Gardening Australia – September 2019

KNOW-HOW

56 SEPTEMBER 2019 GARDENING AUSTRALIA

WHATABOUTSOILPH?

AhighorlowpH–themeasure

ofalkalinityoracidityinthesoil–

canadverselyaffectplants’

nutrientuptake,eveniffertiliseris

present.Asimpletestkit,available

frommostgardencentres,will

giveyouanindicationofthepH

levelsinyourgardenand,thereby,

thetypesofplantsthatwill

flourish.Alwaystakesamples

fromafewplaces,aspHlevels

canvarythroughoutagarden.

AdjustingpHonalargescale

isdifficult.IfyoursoilpHis

unsuitableforaparticularplant,

itmaybeeasiertogrowthe

plantinacontainer,addinglime

toraisepHorsulfurtolowerit,

wherenecessary.

TYPEOFFERTILISERADVANTAGES DISADVANTAGES

Compostand

bulkymanures

Improvessoilstructure

andbiologicalfertility.

Goodmulch.

Slowactingand

comparativelylowin

nutrients.Canbesmelly.

Bloodandbone Gentle,slowfeeding.

Encouragesbeneficial

soilorganisms.

Maynotcontain

potassium(K).

Veryslowrelease.

Organic-based

fertilisers

Encouragesbeneficial

soilorganisms.

Slowacting.Canbesmelly.

Certified-organic

fertilisers

Goodforsoiland

environment.

Canberelatively

expensive.

Inorganicgranular

fertilisers

Formulationsfor

differentplantgroups.

Candamageplantsifnot

appliedcorrectly.

Controlled-release

fertilisers

Littleriskofdamaging

plants.Nutrients

releasedas

temperaturesrise.

Tendtobemore

expensive.

Slow-release

fertilisers

Gentlerelease. Tendtobemoreexpensive.

Lesscontrolovernutrient

releasethancontrolled-

releaseproducts.

Liquidandsoluble

powderfertilisers

Fastrelease.

Manyspecialised

formulationsavailable.

Mustbereappliedoften.

Liquidseaweed Naturalhormones

promoteplanthealth.

Verylowinnutrients,

particularlynitrogen(N),

phosphorus(P)and

potassium(K).

FERTILISERS at a glance

Slow-release fertilisers can be either
organic or inorganic. They allow nutrient
release over a longer period of time,
reducing application frequency. However,
if growing conditions are unsuitable and
the plant can’t make use of the fertiliser,
it can dissipate before it does any good.

Controlled-release fertilisers are the
most technically advanced. Their prills
havepermeableoutercoatingsthat
allowwatertopenetrateanddissolvethe

nutrients within. The nutrient-laden water

then moves back out into the soil or potting

mix. As temperatures rise, the coating

expands, allowing release of more fertiliser

just when plant growth is increasing

(hence the ‘control’). As they are relatively

expensive, these products are most often

used for feeding container plants.

Liquid fertilisers give quick results,

movingrapidlyintotherootsand,toa

limitedextent,thefoliage.Availablein

liquid or soluble powder form, they need

to be reapplied every couple of weeks

or even weekly at half strength. Some

liquids are high in nitrogen, to promote

leafy growth, while others are formulated

to promote flowering, or for other specific

applications. Liquids are a good choice

for feeding seedlings and leafy vegetables.

The popular seaweed extracts that often

come in liquid form are useful for promoting

plantperformance,buttheycan’tbe

regardedasasubstituteforfertilisers. GA

ABOVE RIGHT
Liquid seaweed products contain natural
hormones that promote healthy plants,
but are low in nutrients so are generally
considered tonics rather than fertilisers.