Understanding your soil

Written By Benjamin Campbell

Great gardens aren’t built from the top down, they’re built from the soil up. Whether you’re planting a new garden or maintaining an established one, understanding your soil’s physical and chemical properties is essential for long-term success.

Soil is a living system made up of minerals, organic matter, water, air, and microorganisms. Together, these components influence how plants grow, how water moves, and how nutrients are made available.

This guide breaks down the five key aspects of soil every gardener should understand: texture, structure, drainage, nutrients, and pH.

1. Soil Texture: What Your Soil Is Made Of

Soil texture refers to the relative proportions of sand, silt, and clay particles.

  • Sand: Large particles, gritty feel, drains quickly

  • Silt: Medium particles, smooth texture

  • Clay: Very fine particles, sticky when wet, holds water

Why it matters

Texture determines:

  • Water retention

  • Nutrient holding capacity

  • Ease of root growth

Sandy soils drain quickly but don’t hold nutrients well, while clay soils retain nutrients but can become compacted and poorly aerated. A balanced loam soil is generally ideal for most plants.

2. Soil Structure: How Soil Holds Together

While texture is about particle size, soil structure describes how those particles are arranged into aggregates or “clumps.”

Good soil structure forms small, crumb-like aggregates that:

  • Allow air and water to move freely

  • Support strong root development

  • Encourage beneficial soil biology

Signs of poor structure

  • Hard, compacted soil

  • Surface crusting

  • Water pooling or runoff

Improving soil structure

  • Add organic matter (compost, mulch)

  • Minimise excessive digging or foot traffic

  • Avoid working soil when it’s wet

Unlike texture, structure can be improved over time with good management.

3. Drainage: How Water Moves Through Soil

Drainage refers to how quickly water moves into and through your soil. It’s influenced by both texture and structure.

  • Poor drainage: Water sits on the surface → root rot, lack of oxygen

  • Excessively fast drainage: Water drains too quickly → drought stress

Healthy soil allows water to soak in while still holding enough moisture for plant use.

Simple drainage test

Dig a hole, fill it with water, and observe:

  • Drains within a few hours → well-drained

  • Takes a day or more → poorly drained

Improving drainage

  • Incorporate organic matter

  • Break up compaction

  • Consider raised beds in heavy clay areas

4. Soil Nutrients: Supporting Plant Growth

Plants rely on soil for essential nutrients, including:

  • Macronutrients: Nitrogen (N), Phosphorus (P), Potassium (K)

  • Secondary nutrients: Calcium, Magnesium, Sulfur

  • Micronutrients: Iron, Zinc, Manganese

Why nutrients matter

  • Deficiencies lead to poor growth and yellowing

  • Excess nutrients can harm plants and the environment

Nutrient availability is influenced by:

  • Soil organic matter

  • Drainage

  • Soil pH

5. Soil pH: The Nutrient Gatekeeper

Soil pH measures how acidic or alkaline your soil is.

  • Acidic soils: Below pH 7

  • Neutral soils: Around pH 6–7 (ideal for most plants)

  • Alkaline soils: Above pH 7

Why pH is critical

Even if nutrients are present, plants may not be able to access them if the pH is outside the ideal range.

  • Low pH → some nutrients become overly available

  • High pH → nutrients like iron become harder for plants to absorb

The Importance of Soil Testing

A soil test is the most reliable way to understand your soil. It can reveal:

  • pH levels

  • Nutrient availability

  • Organic matter content

  • Practical recommendations for improvement

Benefits

  • Avoids unnecessary fertiliser use

  • Saves money

  • Leads to healthier, more resilient plants

Bringing It All Together

These five factors don’t work independently, they’re closely linked:

  • Texture influences structure

  • Structure affects drainage

  • Drainage impacts nutrient movement

  • pH controls nutrient availability

Understanding this system allows you to work with your soil rather than against it.

Final Thoughts

Every garden is unique because every soil is different. By understanding your soil’s texture, structure, drainage, nutrients, and pH, you can make smarter decisions about plant selection, soil improvement, and garden design.

Small, consistent improvements, especially adding organic matter, can dramatically improve soil health over time.

If you’re unsure where to begin, a simple soil test is one of the best investments you can make in your garden.

Benjamin Campbell
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Understanding Microclimates in Melbourne Gardens