How Do I Test and Improve My Soil?

Shanti
4 days ago
5 min read

Healthy soil is not defined by one colour, texture or pH. A useful soil must provide plant roots with air, water, nutrients, physical support and a living environment.

Before adding fertiliser, lime, gypsum or compost, identify the actual problem. Unnecessary amendments can waste money, damage plants and allow excess nutrients to move into waterways.

Begin with observation

Inspect the soil in several parts of the garden. Conditions can change over a short distance because of slope, construction, drainage, previous land use and existing vegetation.

Record:

Which plants grow well or poorly
Areas where water pools
Areas that dry rapidly
Compacted paths or bare ground
Soil colour and smell
Root depth
Worms and other visible soil organisms
Recent fertiliser, lime, compost or manure applications
Previous building, industrial or waste activity

Do not judge soil health from the number of earthworms alone. Worm numbers change with moisture, temperature, organic material and soil type.

Examine the soil profile

Dig a small inspection hole away from underground services and important roots.

Look for:

The depth of darker surface soil
Changes in colour or texture
Dense or compacted layers
Gravel, rubble or construction waste
Roots that stop or turn sideways
Grey, greenish or strongly mottled layers that may indicate poor drainage
Unusual odours
Water entering the hole

A surface test cannot reveal every deeper problem. Tree roots, drainage restrictions and subsoil acidity may affect plants even when the topsoil appears healthy.

Test the texture by hand

Moisten a small amount of soil until it can be worked without dripping.

Rub it between your fingers:

Sandy soil feels gritty and usually falls apart easily.
Silty soil feels smooth or floury.
Clay soil feels sticky and can often be shaped into a ribbon.
Loam contains a more balanced mixture of particle sizes.

Texture is largely determined by mineral particle size and cannot be changed easily across a whole garden. Organic matter can improve how many soils function, but it does not turn clay into true loam.

Check drainage and infiltration

After rain, record how long water remains on the surface. You can also use a simple infiltration test:

Push a short open-ended cylinder into the soil.
Add a measured depth of water.
Record how long it takes to soak in.
Repeat the test in several locations.

Very slow infiltration may result from clay, compaction, water-repellent soil or an already saturated profile. Very rapid infiltration may indicate sandy soil with low water-holding capacity.

A single test is only a comparison between areas. Soil moisture and recent weather will affect the result.

Test soil pH

Soil pH describes acidity or alkalinity. It affects nutrient availability, soil organisms and the behaviour of some toxic elements.

Queensland Government guidance notes that many mineral nutrients are readily available when soil is near neutral, but the best range depends on the plant. Some crops prefer moderately acidic soil, while others tolerate alkaline conditions.

Use a soil pH kit or meter according to its instructions. Test several representative areas rather than combining the entire property into one result.

Keep separate samples for:

Vegetable beds
Lawn
Orchard
Native garden
Areas with different soil or management histories

Home kits are useful for screening. A laboratory test is more appropriate when results will guide substantial amendments or when plant problems continue.

When should I use a laboratory?

Consider laboratory testing when:

Establishing a large or valuable garden
Growing food intensively
Applying lime or major nutrient amendments
Plants repeatedly fail without an obvious cause
Salinity or sodicity is suspected
Soil has received repeated manure or fertiliser applications
You need organic carbon or nutrient measurements
You need to compare changes over time

Ask the laboratory which tests suit your intended plants and soil type. A broad test package may include pH, electrical conductivity, organic carbon, major nutrients and exchangeable cations.

Take a representative sample

Follow the laboratory’s instructions. A typical garden sample involves:

Divide the property into areas with similar use and soil.
Remove surface mulch without removing soil.
Take several small samples from the specified depth.
Use clean tools and a clean container.
Mix samples from the same management area.
Remove stones and large organic pieces if instructed.
Label the sample with its location and depth.
Record the sampling date and recent amendments.

Do not combine a healthy bed with a failing area. The average result may hide both conditions.

Sampling depth matters. Results from surface soil cannot be compared reliably with deeper samples.

Treat possible contamination separately

A normal fertility test does not necessarily test for lead, arsenic, hydrocarbons, pesticides or other contaminants.

Obtain specialist advice if the property:

Is beside a busy or historically industrial site
Contains ash, slag, dumped waste or treated timber
Has peeling old paint nearby
Was previously used for workshops, fuel storage or intensive agriculture
Has imported fill of unknown origin
Produces unusual odours or staining

Avoid growing food directly in suspect soil until the risk has been assessed. Clean raised beds with a physical separation layer may reduce contact, but they do not remove contamination from the property.

Match improvement to the problem

Low organic matter

Add mature compost, retain suitable plant residues, use organic mulch and keep living roots in the soil where practical.

Compaction

Avoid working wet soil, keep feet and machinery out of growing beds, use permanent paths and protect the surface with mulch. Severe subsoil compaction may need professional assessment.

Poor drainage

Determine whether the cause is compaction, clay, a low point, a blocked drain or a shallow water table. Adding more soil to the surface may not correct the underlying problem.

Low pH

Apply lime only after confirming the pH, crop requirement, soil type and recommended rate. Over-liming can create nutrient problems and is difficult to reverse.

High pH

Do not try to lower a large alkaline garden quickly with household acids. Select tolerant plants or obtain soil-specific advice before using an acidifying amendment.

Nutrient deficiency

Confirm the likely deficiency through symptoms, plant requirements and preferably a soil or tissue test. Apply only the nutrient and rate required.

Sandy soil

Use mature compost and surface mulch to support water and nutrient retention. Smaller, more frequent watering may be more effective than heavy watering.

Clay soil

Protect the soil from compaction, maintain surface organic matter and choose plants suited to its drainage. Gypsum is useful for particular sodic soils; it is not a universal treatment for every clay.

Improve one area at a time

For a new garden bed:

Observe drainage and sunlight.
Test pH.
Obtain a laboratory test if the investment or problem justifies it.
Correct a confirmed major constraint.
Add a moderate amount of mature compost if appropriate.
Mulch the surface.
Choose plants suited to the conditions.
Record plant performance.
Retest after enough time has passed for management to have an effect.

Evidence and limitations

Soil tests are decision tools, not complete measures of soil health. Results must be interpreted for the soil type, sampling depth, climate and intended plants.

Evidence A includes current Queensland and Victorian government soil guidance. Evidence B includes recognised soil-science research showing that excessive nutrient additions can accumulate and increase environmental risk.

Related Earth Resource Map indexes

Soil Health & Biology
Soil Rehabilitation & Land Repair
Climate & Site Selection
Garden Planning

References

Agriculture Victoria. (2026). Understanding soil tests for pastures. Evidence A.

Queensland Government. (2013). Soil pH. Evidence A.

Queensland Government. (2025). What is my soil type?. Evidence A.

Wells, A. T., Chan, K. Y., & Cornish, P. S. (2008). Phosphorus accumulation and other changes in soil properties as a consequence of vegetable production. Australian Journal of Soil Research, 46(2), 167–176. CSIRO Publishing. Evidence B.