General Plant Health and Mineral Deficiencies

Pesticides and Garden Health

Pesticides can be useful tools. There. That’s the statement of the 20^th Century.

However, we are in the 21^st Century and we now understand that unnecessary pesticide use can affect:

target pests
beneficial insects
predators
soil organisms
water
wider ecosystems

The preferred approach is usually: prevention → monitoring → identification → targeted intervention (rather than spray everything.)

Integrated Pest Management

Integrated Pest Management, or IPM, considers:

prevention
monitoring
identification
biological control
cultural control
physical control
chemical control where justified

Chemical control becomes one tool within a wider strategy rather than the automatic first response.

Garden Health and Mowing

Mowing is a good example of how management affects biodiversity.

A very short lawn:

reduces flowering opportunities
can reduce habitat
may increase stress during drought

A less intensively managed lawn can provide:

flowers
insects
seed
shelter

However, formal lawns have legitimate uses. Therefore the answer is not, “Never mow!”

The answer is, “Mow according to purpose.”

Introduction to Observation

A healthy plant is more than a plant with green leaves.

Good plant health means that a plant is able to:

grow normally
produce healthy leaves and stems
develop a strong root system
flower or fruit appropriately
resist or tolerate environmental stresses
recover from minor damage
complete its natural life cycle

A horticulturist needs to be able to recognise when something is wrong before deciding what treatment to use. Observe and record everything. The most important rule is: Diagnose before you treat.

A yellow leaf does not automatically mean that a plant needs fertiliser.

The problem could be:

nutrient deficiency
nutrient toxicity
drought
waterlogging
poor drainage
unsuitable pH
root damage
pests
disease
temperature
frost
excessive shade
physical damage
natural ageing

Signs of Plant Ill Health

Before feeding, inspect the whole plant.

Look for:

Leaves

yellowing
browning
curling
spots
distortion
premature leaf fall

Stems

weak growth
dieback
lesions
cracking
unusual swelling

Roots

poor rooting
rotting
discolouration
lack of fine roots

Flowers

poor flowering
flower drop
distorted flowers

Overall growth

stunting
wilting
weak shoots
poor vigour

Nutrient Deficiency or Something Else?

This is one of the most important skills in horticulture. A yellow leaf does not automatically mean, “The plant needs fertiliser.”

Yellowing can be caused by:

nitrogen deficiency
iron deficiency
waterlogging
drought
root damage
pests
disease
unsuitable pH
natural ageing

The gardener must consider the whole situation.

Symptoms of Possible Nitrogen Deficiency

Possible signs include:

general pale green colour
yellowing of older leaves
reduced growth
smaller leaves

Nitrogen deficiency often affects older foliage first because nitrogen can be redistributed within the plant.

Symptoms of Possible Iron Deficiency

Iron deficiency can produce:

interveinal chlorosis

The newer leaves may become yellow while the veins remain relatively green.

This can occur where iron is unavailable because of soil conditions such as high pH.

Adding iron without correcting the underlying condition may not provide a lasting solution.

Nutrient Toxicity

More fertiliser can be harmful. Excessive fertiliser may cause:

root damage
leaf scorch
poor growth
salt accumulation
nutrient imbalance

This is why following application rates is essential.

Soil pH and Nutrient Availability

Soil pH affects how available nutrients are to plants.

A nutrient may be present in the soil but unavailable to the plant.

This is called nutrient availability.

For example, high soil pH can reduce the availability of some micronutrients, including iron.

Therefore: Nutrient present ≠ nutrient available.

Feeding and Watering

Fertiliser should not be applied blindly to dry, stressed plants.

Where appropriate, ensure the growing medium has adequate moisture before applying fertiliser.

However, avoid waterlogging.

The objective is: adequate moisture + appropriate nutrients + healthy roots

Fertiliser and the Environment

Excess nutrients can leave the growing area through:

surface runoff
leaching
drainage

Nutrients entering watercourses can contribute to eutrophication.

This can cause excessive algal and plant growth, followed by oxygen depletion as organic material decomposes.

Responsible horticulture therefore means:

Apply only what is required, where it is required, when it is required.

Fertiliser Application Safety (Do not mix products unless the manufacturer specifically permits it.)

Always:

read the label
follow application rates
use appropriate PPE
store fertiliser safely
avoid contamination of water
wash hands after use
keep products in their original containers
follow COSHH requirements where applicable

PPE

Task	Potential hazard	Typical PPE / control
Handling granular fertiliser	Dust/contact	Gloves; avoid creating dust
Mixing liquid feed	Splash/contact	Gloves and eye protection where required
Applying fertiliser	Skin/eye contact	Gloves and suitable clothing
Using concentrated products	Chemical exposure	Follow label and COSHH assessment where applicable
Cleaning equipment	Residues	Gloves; appropriate hygiene
Storing fertiliser	Spills/contamination	Secure, dry and labelled storage

PPE should be selected following the risk assessment and product instructions.

Practical Feeding Assessment

Choose a plant that appears unhealthy.

Observe

What can you see?

Leaves

Stems

Soil

Roots, if visible

Growing conditions

☐ Full sun

☐ Partial shade

☐ Shade

☐ Dry

☐ Moist

☐ Waterlogged

Possible cause

Is feeding appropriate?

YES / NO / NOT YET

Liquid Feed Practical

Plant: ______________________________

Fertiliser: ___________________________

NPK: ________________________________

Recommended dilution: ________________

Amount of water: _____________________

Amount of fertiliser: __________________

Application date: _____________________

What happened after feeding?

Was the plant healthier?

Solid Feed Practical

Plant/area: ___________________________

Fertiliser: ___________________________

Application rate: _____________________

Area treated: _________________________

Amount applied: _______________________

Application date: _____________________

Why was this fertiliser selected?

Student Questions

1. Why do plants require nutrients?

2. What does NPK stand for?

3. Give two functions of nitrogen.

4. Why might a container plant require more regular feeding than an established plant growing in the ground?

5. What is the difference between liquid and solid fertiliser?

6. Why should fertiliser not automatically be applied to a yellow plant?

7. Give three possible causes of yellow leaves that are not nutrient deficiency.

8. Why should plants not normally be fed while severely drought stressed?

9. Why can excessive fertiliser damage plants?

10. Why is soil pH important when considering plant nutrition?

11. Why is it important not to apply more fertiliser than recommended?

12. When are plants generally most likely to benefit from feeding?

The Professional Feeding Decision

Before feeding, ask:

1. Is the plant actually deficient in nutrients?

↓

2. Could something else be causing the symptoms?

↓

3. Is the plant actively growing?

↓

4. Is the soil adequately moist but not waterlogged?

↓

5. Is the soil pH suitable?

↓

6. Is feeding appropriate for this species?

↓

7. Which fertiliser is appropriate?

↓

8. Liquid or solid?

↓

9. What is the correct application rate?

↓

10. How will I monitor the result?

Remember

Fertiliser is plant food only in a very simplified sense. Plants manufacture their own food through photosynthesis. Fertilisers provide mineral nutrients required for healthy growth. The professional gardener therefore does not think:

“The plant looks ill – give it fertiliser.”

Instead, think:

“The plant looks ill – why?”

Only after identifying the likely cause should feeding be considered. Good plant nutrition is about balance. Too little can cause deficiency. Too much can cause toxicity and the wrong fertiliser, applied at the wrong time, can do more harm than good. The best horticulturist is therefore not the person who feeds the most. It is the person who knows, when to feed, what to feed, how much to feed, how to apply it, and when not to feed at all.

Key references

Royal Horticultural Society (RHS), guidance on feeding plants, fertilisers, plant nutrition and soil management.
Royal Horticultural Society (RHS), guidance on understanding soil pH and nutrient availability.
Health and Safety Executive (HSE), guidance on Control of Substances Hazardous to Health (COSHH).
Control of Substances Hazardous to Health Regulations 2002.
Fertiliser Regulations 1991, as amended.
Agriculture Act 1970, relevant provisions concerning fertilisers and agricultural products.
Taiz, L. et al., Plant Physiology and Development.

Quick Mineral Deficiency Guide

Nutrient	Possible symptoms	Where symptoms often appear
Nitrogen	General yellowing, weak growth	Older leaves
Phosphorus	Poor growth, dark/green-purple foliage in some plants	Older growth
Potassium	Marginal yellowing/scorching	Older leaves
Magnesium	Interveinal chlorosis	Older leaves
Sulphur	General chlorosis, poor growth	Younger growth
Calcium	Distorted young growth, tip damage	Young leaves/growing points
Iron	Interveinal chlorosis	Young leaves
Manganese	Interveinal chlorosis, spotting	Often younger leaves
Zinc	Small leaves, shortened internodes	Young growth
Copper	Tip dieback, distortion	Young growth
Boron	Distorted growing points, poor roots	Young growth
Molybdenum	Chlorosis, poor growth	Variable

This table is a diagnostic aid, not a substitute for testing.

Mobile vs Immobile Nutrients

A useful Level 2 concept is:

Mobile nutrients

The plant can move them from older tissues to younger tissues. Examples include, nitrogen; phosphorus; potassium; magnesium

Deficiency often becomes visible first in older leaves.

Relatively immobile nutrients

They are not readily moved around the plant.

Examples include, calcium; boron; iron.

Deficiency symptoms often become visible first in younger growth.

This is one of the most useful patterns to remember.

Nutrient Deficiency vs pH

A plant may have enough of a nutrient in the soil but still show deficiency symptoms.

Why?

Because the nutrient may be unavailable.

Soil pH influences nutrient availability.

For example:

high pH can reduce the availability of iron and some other micronutrients
very low pH can affect the availability or toxicity of several elements

This is why soil testing can be useful.

Nutrient Deficiency vs Waterlogging

Waterlogged soil can cause root problems.

Roots require oxygen.

When soil pores remain filled with water:

oxygen availability falls

Root function can decline.

The plant may then show:

yellow leaves
poor growth
wilting
root death

This can look like nutrient deficiency.

Adding fertiliser to a waterlogged plant is unlikely to solve the underlying problem.

Nutrient Deficiency vs Drought

Drought-stressed plants may show:

wilting
curling
browning
premature leaf fall
reduced growth

Do not automatically feed a drought-stressed plant.

First consider:

Does the plant have access to sufficient water?

Nutrient Deficiency vs Pests

Pests may cause:

yellowing
leaf distortion
holes
stippling
leaf curling
sticky honeydew
premature leaf drop

Look carefully at:

leaf undersides
growing points
stems
buds

Use a hand lens where appropriate.

Nutrient Deficiency vs Disease

Diseases can cause:

leaf spots
lesions
dieback
wilting
cankers
distortion
premature leaf fall

Look for patterns.

A nutrient deficiency may affect a large part of the plant relatively uniformly.

A disease may produce:

discrete spots
lesions
patches
progressive areas of damage

This is not an absolute rule, but it can be a useful clue.

Signs of General Plant Stress

Watch for:

☐ Yellowing

☐ Browning

☐ Wilting

☐ Leaf curling

☐ Leaf drop

☐ Stunted growth

☐ Poor flowering

☐ Poor fruiting

☐ Shoot dieback

☐ Distorted leaves

☐ Weak stems

☐ Root rot

☐ Excessive pest activity

☐ Unusual spots or lesions

The earlier a problem is identified, the greater the opportunity for effective intervention.

The Five-Question Diagnosis

When a plant looks unhealthy, ask:

1. What has changed?

Has the plant recently been:

planted?
pruned?
moved?
watered differently?
fertilised?

2. Where is the damage?

old leaves?
young leaves?
roots?
stems?
flowers?

3. What is the pattern?

Is it:

uniform?
patchy?
spotted?
along leaf margins?
between veins?

4. What are the growing conditions?

Check:

soil moisture
drainage
light
temperature
pH
compaction

5. Are there pests or diseases?

Inspect carefully before assuming a nutritional problem.

When to Test the Soil

Soil testing may be appropriate where:

symptoms persist
several plants show similar problems
nutrient deficiency is suspected
pH may be unsuitable
fertiliser programmes are being planned

Testing can provide evidence rather than relying entirely on visual diagnosis.

Why Overfeeding Can Be Dangerous

Applying nutrients without evidence can result in:

toxicity
salt accumulation
nutrient imbalance
root damage
excessive soft growth
environmental pollution

Some nutrients can interfere with the uptake of others.

For example:

Too much of one nutrient can contribute to an imbalance involving another.

Therefore:

Do not treat a plant deficiency you have not identified.

General Plant Health Management

Good plant health begins with prevention.

Provide:

Correct plant

Choose a plant suited to the site.

Correct soil

Consider:

texture
structure
drainage
pH
fertility

Correct water

Avoid both drought and waterlogging.

Correct light

Match the plant to:

sun
partial shade
shade

Correct nutrition

Feed only when appropriate.

Correct pruning

Use suitable pruning techniques and timing.

Good hygiene

Clean tools and remove diseased material appropriately.

Monitoring

Regularly inspect plants.

Seasonal Plant Health

Season	What to look for
Spring	New growth, pests, frost damage, nutrient symptoms
Summer	Drought, heat stress, pests, diseases, water demand
Autumn	Natural leaf senescence, disease, nutrient redistribution
Winter	Frost damage, waterlogging, wind damage, dormant pests

Remember:

Not every colour change is a disease or deficiency.

Autumn leaf colour and leaf fall are normal biological processes for deciduous plants.

Practical Plant Health Inspection

Choose one plant.

Plant name: ______________________________

Date: ___________________________________

Location: ________________________________

Season: __________________________________

Leaf condition

☐ Healthy

☐ Yellow

☐ Brown

☐ Spotted

☐ Distorted

☐ Curling

☐ Wilting

Stem condition

☐ Healthy

☐ Dieback

☐ Lesions

☐ Distortion

☐ Weak growth

Soil

☐ Dry

☐ Moist

☐ Waterlogged

☐ Compacted

Pests observed?

☐ Yes

☐ No

Disease symptoms observed?

☐ Yes

☐ No

Possible nutrient deficiency?

☐ Yes

☐ No

☐ Unsure

Diagnosis

What is the main symptom?

Where does it occur?

Is it mainly on old or young growth?

What other possible causes have you considered?

What evidence supports your diagnosis?

What action would you recommend?

Student Mineral Deficiency Challenge

Match the symptom to the most likely nutrient.

A

Older leaves become yellow throughout.

Possible nutrient:

B

Older leaves develop yellow tissue between green veins.

Possible nutrient:

C

Young leaves become yellow between green veins.

Possible nutrient:

D

Leaf margins become yellow and then brown.

Possible nutrient:

E

Young growing points become distorted or die back.

Possible nutrient:

Important Reminder

The answers above are possible diagnoses, not guaranteed diagnoses.

For example:

Interveinal chlorosis

could involve:

magnesium
iron
manganese

depending on:

plant species
leaf age
soil pH
growing conditions
other factors

A professional horticulturist uses symptoms as evidence, not as an automatic answer.

Practical Observation Exercise

Take two plants:

Plant A: apparently healthy

Plant B: showing signs of ill health

Compare them.

Feature	Plant A	Plant B
Leaf colour
Leaf size
Leaf shape
Shoot growth
Flowering
Soil moisture
Pest evidence
Disease evidence
Overall condition

What is different?

What might explain the difference?

Student Questions

1. What does chlorosis mean?

2. What does necrosis mean?

3. Why can yellow leaves have many different causes?

4. What is the difference between a mobile and relatively immobile nutrient?

5. Name four nutrients that are relatively mobile within plants.

6. Name three nutrients whose deficiency may first affect younger growth.

7. What is interveinal chlorosis?

8. Why is soil pH important for plant nutrition?

9. Why should a gardener inspect for pests before applying fertiliser?

10. Why can overfeeding be harmful?

The Professional Plant Health Checklist

Before treating an unhealthy plant:

LOOK

What symptoms can you see?

↓

LOCATE

Where are the symptoms?

↓

COMPARE

Is new or old growth affected?

↓

CHECK

Look at soil, roots, pests and diseases.

↓

CONSIDER

Water, light, temperature, pH and nutrition.

↓

TEST

Use soil or other appropriate tests where necessary.

↓

DIAGNOSE

Identify the most likely cause.

↓

TREAT

Use the least harmful effective intervention.

↓

MONITOR

Check whether the plant responds.

Remember

Healthy plants are not necessarily perfect plants.

A small amount of insect damage, an occasional blemish or natural seasonal change does not automatically mean that a plant requires treatment.

Good horticulture is about observation and balance.

When a plant looks unhealthy, resist the temptation to immediately:

feed it, spray it, prune it or water it.

First ask:

What is the plant telling me?

The leaves may be giving you clues about nutrients.

The roots may be telling you about waterlogging.

The soil may be telling you about pH or compaction.

The pattern of damage may indicate a pest or disease.

And the season may explain something that looks alarming but is actually completely normal.

The skilled horticulturist learns to read the plant before treating the plant.

Key references

Royal Horticultural Society (RHS), guidance on plant health, plant nutrition, pests, diseases and disorders.
Royal Horticultural Society (RHS), guidance on soil, pH and nutrient availability.
Health and Safety Executive (HSE), guidance on safe use of horticultural products.
Taiz, L. et al., Plant Physiology and Development.
Marschner, P., Marschner’s Mineral Nutrition of Higher Plants.
Mengel, K. and Kirkby, E.A., Principles of Plant Nutrition.

What Does a Healthy Plant Look Like?

A healthy plant will normally show characteristics appropriate to its species.

Look for:

Leaves

appropriate colour
good size
normal shape
firm texture
no unexplained spots or lesions

Stems

appropriate strength
normal colour
healthy growing points
no unexplained dieback

Roots

Healthy roots are generally:

well distributed
firm
actively growing
appropriate in colour for the species

Rotting roots may be:

dark
soft
unpleasant smelling

Flowers and fruit

Healthy plants should produce flowers and fruit appropriate to their:

species
age
season
growing conditions

The Plant Health Check

A simple plant-health inspection can follow this sequence:

LOOK

↓

TOUCH

↓

SMELL

↓

CHECK THE SOIL

↓

CHECK THE ROOTS IF APPROPRIATE

↓

LOOK FOR PESTS

↓

LOOK FOR DISEASE

↓

CONSIDER NUTRIENTS

↓

CONSIDER THE ENVIRONMENT

↓

DIAGNOSE

Start with the Whole Plant

Do not immediately focus on the damaged leaf.

Ask:

Where is the damage occurring?

Is it:

old leaves?
young leaves?
growing points?
stems?
roots?
flowers?
fruit?
the whole plant?

The position of symptoms can provide valuable clues.

Older Leaves or Younger Leaves?

This is one of the most useful clues when considering mineral deficiencies.

Some nutrients are mobile within the plant.

If they are in short supply, the plant can move them from older leaves to younger growing tissue.

Other nutrients are relatively immobile.

Deficiency symptoms therefore often appear first in young growth.

This gives us a useful diagnostic principle:

Older leaves affected first

Consider deficiencies of mobile nutrients such as:

nitrogen
phosphorus
potassium
magnesium

Younger leaves affected first

Consider deficiencies of relatively immobile nutrients such as:

calcium
iron
boron

This is a useful guide rather than an absolute rule.

What is Chlorosis?

Chlorosis means a loss of green colour from plant tissue.

Leaves may become:

pale green
yellow
yellow-white

Chlorosis can have many causes.

It may be associated with:

nitrogen deficiency
iron deficiency
magnesium deficiency
manganese deficiency
waterlogging
root damage
unsuitable pH
disease

Therefore:

Yellow leaves do not automatically mean nitrogen deficiency.

What is Necrosis?

Necrosis means the death of plant tissue.

It can appear as:

brown patches
dead leaf margins
blackened tissue
scorched areas
dead shoots

Necrosis may be caused by:

nutrient deficiency
nutrient toxicity
drought
frost
disease
chemical damage
root problems

Again, context is essential.

Macronutrients

Plants require relatively large quantities of certain mineral nutrients.

These include:

Nitrogen (N)

Phosphorus (P)

Potassium (K)

They also require:

Calcium (Ca)

Magnesium (Mg)

Sulphur (S)

Nitrogen Deficiency

Nitrogen is important for:

leaf growth
chlorophyll
proteins
vegetative growth

Possible symptoms

pale green leaves
general yellowing
reduced growth
small leaves
weak shoots

The symptoms may begin with older leaves because nitrogen is mobile within the plant.

Memory tip

Nitrogen = New growth

Think:

N = New leaves and shoots

But remember that nitrogen deficiency is only one possible cause of pale foliage.

Excess Nitrogen

Too much nitrogen can also cause problems.

Possible effects include:

excessive soft growth
large, lush foliage
reduced flowering
weak stems
increased susceptibility to some pests and diseases
poor winter hardiness in some plants

The lesson is:

More is not always better.

Phosphorus Deficiency

Phosphorus is involved in:

energy transfer
root development
reproductive development

Possible symptoms can include:

poor growth
poor root development
darker green or purplish foliage in some plants
delayed maturity

However, phosphorus deficiency is often difficult to diagnose visually.

Environmental factors and species differences can alter symptoms.

Important

Do not automatically add phosphorus simply because a plant is growing poorly.

Potassium Deficiency

Potassium has an important role in:

water regulation
enzyme activity
metabolism
plant strength

Possible symptoms include:

yellowing around leaf margins
brown or scorched margins
weak growth
poor quality or reduced yield in crops

Symptoms may develop first on older leaves.

Memory tip

Potassium = edges

Think:

K deficiency → leaf edges may show damage.

Magnesium Deficiency

Magnesium is an important component of chlorophyll.

A common symptom is:

interveinal chlorosis

This means:

the tissue between the veins becomes yellow while the veins remain greener.

It often appears first on older leaves because magnesium is mobile.

Memory tip

Magnesium = Middle of the leaf

Look between the veins.

Sulphur Deficiency

Sulphur is required for:

amino acids
proteins
enzymes

Deficiency can result in:

pale or yellow foliage
reduced growth

Unlike nitrogen deficiency, sulphur deficiency may appear more strongly in younger growth.

This distinction can help with diagnosis.

Calcium Deficiency

Calcium is important for:

cell walls
cell membranes
root growth
growing points

Because calcium is relatively immobile, symptoms can appear in:

young leaves
shoot tips
root tips

Possible symptoms include:

distorted young leaves
damaged growing points
poor root growth
tip dieback

Important

Calcium problems can be related to water movement, not simply the total amount of calcium in the soil.

Micronutrients

Plants also require nutrients in much smaller quantities.

These include:

iron
manganese
zinc
copper
boron
molybdenum
chlorine
nickel

Small requirement does not mean small importance.

Iron Deficiency

Iron is important for chlorophyll formation and other plant processes.

A classic symptom is:

interveinal chlorosis of young leaves

The veins may remain green while the tissue between them becomes yellow.

It is particularly common where soil or growing-medium conditions make iron less available.

For example, high pH can reduce iron availability.

Memory tip

Iron = young leaves go pale

Manganese Deficiency

Manganese is involved in:

photosynthesis
enzyme activity

Possible symptoms include:

interveinal chlorosis
small necrotic spots
reduced growth

Symptoms can resemble other deficiencies.

Do not diagnose manganese deficiency simply from leaf colour.

Zinc Deficiency

Zinc is involved in:

enzyme activity
growth regulation
development

Possible symptoms include:

small leaves
shortened internodes
distorted growth
chlorosis

Plants may develop a compact or “rosetted” appearance.

Copper Deficiency

Copper is involved in:

enzymes
photosynthesis
reproductive development

Possible symptoms can include:

dieback of shoot tips
distorted young leaves
poor flowering
weak growth

Copper deficiency is relatively uncommon in many garden situations.

Boron Deficiency

Boron is important for:

cell wall development
growing points
reproductive development

Possible symptoms include:

distorted young growth
damaged growing points
poor root development
poor fruit or seed development

Boron is required in very small amounts.

This makes it particularly important not to apply it unnecessarily.

Too much boron can be toxic.

Molybdenum Deficiency

Molybdenum is required in very small amounts but is important in plant nitrogen metabolism.

Deficiency can cause:

poor growth
chlorosis
leaf distortion

Symptoms vary between species.

Feeding Plants – Liquid and Solid Fertilisers

Introduction

Plants, like all living organisms, require a range of nutrients to grow successfully.

However, feeding a plant does not simply mean adding fertiliser whenever it looks unhealthy.

A plant may be struggling because of:

lack of water
waterlogging
poor drainage
unsuitable pH
pests
diseases
root damage
poor light
temperature stress
compacted soil
nutrient deficiency

Adding fertiliser to an unhealthy plant without identifying the cause can sometimes make the situation worse.

The professional approach is:

Observe → Diagnose → Decide → Feed if necessary → Monitor

Why Do We Feed Plants?

Plants obtain most of their carbon from the atmosphere through photosynthesis.

They obtain water and mineral nutrients primarily through their roots.

Nutrients are required for processes including:

photosynthesis
cell division
root development
flowering
fruit production
enzyme activity
healthy leaves and stems

Plants require nutrients in different quantities.

The major nutrients include:

Macronutrients

Nitrogen (N)
Phosphorus (P)
Potassium (K)

Plants also require other macronutrients, including:

calcium
magnesium
sulphur

Micronutrients

Required in smaller quantities, including:

iron
manganese
boron
copper
zinc
molybdenum
chlorine
nickel

Small quantity does not mean unimportant.

A deficiency of a micronutrient can still seriously affect plant growth.

What Does NPK Mean?

Fertiliser labels commonly display three numbers.

For example:

7–7–7

These represent the relative percentages of:

N – Nitrogen

P – Phosphate

K – Potash

They are not simply a score showing how “strong” the fertiliser is.

The numbers describe the nutrient content of the product.

Always read the manufacturer’s label.

Nitrogen (N)

Nitrogen is particularly important for:

leaf growth
shoot growth
chlorophyll production
overall vegetative development

A shortage can result in:

pale leaves
yellowing, particularly of older leaves
weak growth
reduced vigour

However, excessive nitrogen can also cause problems.

Too much nitrogen may produce:

soft, lush growth
excessive vegetative growth
reduced flowering
increased susceptibility to some pests and diseases
poor overwintering in some plants

More nitrogen is therefore not automatically better.

Phosphorus (P)

Phosphorus is involved in:

energy transfer
root development
reproductive growth

Severe phosphorus deficiency can affect growth and development.

However, phosphorus deficiency is often over-diagnosed.

In many garden soils, sufficient phosphorus is already present.

Adding more phosphorus without a demonstrated need is not necessarily beneficial.

Potassium (K)

Potassium is important in:

water regulation
enzyme activity
plant metabolism
general plant strength

Adequate potassium contributes to healthy plant functioning and can be particularly important in crops where quality and flowering or fruiting are important.

Deficiency symptoms can include:

marginal leaf scorching
yellowing
weak growth

Again, symptoms can have several possible causes.

Secondary Nutrients

Plants also require:

Calcium

Important for:

cell walls
growing points
root development

Magnesium

Important because it is a central component of chlorophyll.

Deficiency can cause interveinal chlorosis, where the tissue between the veins becomes pale while the veins remain greener.

Sulphur

Important in:

proteins
enzymes
plant metabolism

Micronutrients

Plants require relatively small amounts of micronutrients.

Examples include:

iron
manganese
zinc
copper
boron
molybdenum

Deficiency symptoms can include:

chlorosis
distorted growth
poor flowering
dead growing points
poor root development

However, diagnosing micronutrient deficiency from appearance alone can be difficult.

Feeding Is Not the Same as Watering

Fertiliser supplies nutrients. Water supplies water.

A plant can be well watered but nutrient deficient or well fed but drought stressed.

Giving fertiliser to a severely drought-stressed plant is not a substitute for supplying appropriate water.

Liquid Feed

Liquid fertilisers are dissolved in water before application.

They can be applied:

around the root zone
to growing media
as a foliar feed where the product is specifically designed for this purpose

Liquid feeds are useful when nutrients need to be made available relatively quickly.

Advantages of Liquid Feed

Liquid feed can:

provide nutrients quickly
be accurately diluted
be useful for container-grown plants
be incorporated into irrigation systems where appropriate
provide regular low-dose feeding

It is particularly useful where plants have limited access to nutrients, such as in containers.

Disadvantages of Liquid Feed

Liquid fertiliser can:

be over-applied
cause root damage if too concentrated
be washed away
require regular application
create environmental problems if it reaches watercourses

The correct dilution is therefore essential.

More fertiliser does not mean faster or better growth.

Correct Application of Liquid Feed

Always:

Read the label.
Measure the correct amount.
Dilute according to instructions.
Apply evenly.
Avoid unnecessary contact with foliage unless the product is intended for foliar use.
Avoid contamination of watercourses.
Clean equipment appropriately.

Do not guess the concentration.

Solid Fertilisers

Solid fertilisers are applied in a solid form.

They may be:

granular
pelleted
powdered
slow-release
controlled-release

They can be applied to:

soil
beds
borders
lawns
containers

The release rate depends on the type of fertiliser and environmental conditions.

Advantages of Solid Feed

Solid fertilisers can:

provide nutrients over a longer period
reduce the frequency of application
be useful for beds and borders
provide a steady nutrient supply where appropriate

Controlled-release fertilisers can be particularly useful in containers.

Disadvantages of Solid Feed

Problems can occur if fertiliser is:

over-applied
applied unevenly
placed directly against stems
applied to unsuitable soil
applied during drought
allowed to contaminate water

Excess fertiliser can cause salt injury and damage roots.

Liquid vs Solid Feed

Liquid feed	Solid feed
Mixed with water	Applied as a solid
Nutrients can become available quickly	Release may be slower
Useful for containers	Useful for beds and borders
Requires accurate dilution	Requires accurate application rate
Can be applied regularly	May require fewer applications
Easy to over-concentrate	Easy to over-apply
Useful during active growth	Often useful as part of planned feeding

Neither is automatically better.

The choice depends on:

plant
soil
growing system
season
nutrient requirement
fertiliser formulation

Organic Matter vs Fertiliser

Compost, well-rotted manure and other organic materials can improve soil condition and contribute nutrients.

They can also improve:

soil structure
water-holding capacity
biological activity
nutrient retention

However:

Organic matter is not simply another name for fertiliser.

Its nutrient content can vary considerably.

Healthy soil management is generally about more than applying fertiliser.

Feeding Plants in the Ground

Established plants growing in good soil may require little additional fertiliser.

Before feeding, consider:

soil fertility
plant species
growth rate
previous fertiliser applications
soil pH
organic matter
weather
plant health

A mature shrub in fertile soil does not necessarily need feeding simply because the calendar says it is spring.

Feeding Container Plants

Container plants are different.

The growing medium has a limited volume.

Nutrients can be:

used by the plant
leached away by watering
depleted over time

Consequently, container plants often benefit from a planned feeding programme during active growth.

This is particularly important for:

bedding plants
fruit in containers
vegetables
flowering plants
long-term container specimens

When Should Plants Be Fed?

Many plants are best fed during periods of active growth.

This generally means:

Spring → summer

The exact timing depends on:

species
climate
growing conditions
soil
fertiliser type

Some plants have specific feeding requirements.

Always follow the requirements of the individual plant and fertiliser manufacturer.

Spring Feeding

Spring is often an important feeding period because many plants are beginning active growth.

Feeding may support:

new shoots
leaves
roots
flowering
fruit development

However, do not automatically fertilise every plant in spring.

Assess the plant first.

Summer Feeding

Plants can continue active growth during summer.

Container-grown plants may require regular feeding because nutrients can be depleted.

However, feeding during very hot or dry conditions should be approached carefully.

Deal with drought stress first.

Autumn Feeding

Autumn feeding depends on the plant and fertiliser.

A balanced approach is important.

Avoid encouraging excessive soft growth late in the season where this could reduce winter hardiness.

Some plants benefit from autumn applications formulated for particular purposes, but this is not a reason to apply fertiliser indiscriminately.

Winter Feeding

Most outdoor plants have reduced growth during winter.

Routine feeding is generally unnecessary for dormant plants.

Applying fertiliser when the plant cannot make effective use of it can result in:

nutrient loss
environmental pollution
unnecessary expenditure

When NOT to Feed

Do not automatically feed a plant when it is:

Severely drought stressed

Water appropriately first.

Waterlogged

Investigate drainage and root health.

Recently transplanted

The priority may be root establishment and appropriate watering rather than immediate fertilisation.

Dormant

Many dormant plants have little need for additional nutrients.

Diseased

Identify and manage the disease rather than assuming nutrients are the answer.

Suffering from root damage

Fertiliser will not repair damaged roots.

Growing in very hot conditions

Avoid unnecessary stress and follow product instructions.

Feeding Newly Planted Plants

Newly planted plants should normally be given the opportunity to establish their roots.

Good planting practice includes, suitable soil preparation; correct planting depth; adequate watering; appropriate mulching; protection from competition.

Feeding requirements depend on the plant and soil. More fertiliser does not necessarily mean faster establishment.