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When It’s time To Talk Dirty…Soils Ain’t Soils

Dirt… Sandy Loam… Top Soil… Growing Media… These are just a few terms in the marketplace describing soil. But what do these terms mean? And more importantly, how do you ensure you are getting the appropriate soil for your specific needs?

One of the biggest misconceptions about soil is you can use one type for everything... there is too much variation in soil types to have a 'One-Size-Fits-All' solution. Deciding which soil type to use starts with understanding the nature of raw soil and the different mixes that can be made with soil.

The four main types of soil are

  • Clay soil 
  • Sandy soil
  • Silty soil 
  • Loamy soil

Soil can be classified into 3 primary categories based on its texture – sand, silt, and clay. However, the percentage of these can vary, resulting in more compound types of soil such as loamy sand, sandy clay, silty clay etc.

Characteristics of these soil types are

Clay Soil

  • Sticky, lumpy texture, especially when wet.
  • Drains poorly and can become waterlogged, reducing root growth.
  • High in nutrients

Sandy Soil

  • Gritty, large particles
  • Drains quickly and dries out fast.
  • Low in nutrients as the large particles allow them to be washed out easily.

Silty Soil

  • Slippery when wet with very fine particles.
  • Retains moisture well
  • Rich in nutients

Loam

  • A balance of sand, silt & clay.
  • Good drainage but still can retain moisture
  • Holds nutrients for good plant growth.

So, this is earth in its basic form. Soil deposits can vary dramatically depending on the location and natural environmental (or manmade) factors. Generally, these soils are not ‘fit-for-purpose’ when it comes to landscaping and gardening. So, how does the soil get improved?

Soil manufacturers usually take in raw soil from development sites and the characteristics of this raw soil can vary based on the location of the soil deposit. These manufacturers will then screen the soil, mix in organic matter and let it sit in a pile (windrow) so it develops heat. This helps initial breakdown of the organic matter and reduce inherent weeds.

Landscaping Outlets that stock soils usually have a range of soils that fulfill different purposes. When you decide to purchase soil, always ensure you are clear about its purpose.

These can range from

  • Garden beds and planter boxes
  • Under turf
  • Top dressing lawns 
  • Back filling
  • Levelling

Due to the differing nature of soils, it is difficult to use one soil type for multiple purposes. Trying to use a soil not suited to the job at hand will result in a poor result and more outlay to rectify.

Things to consider when establishing your soil choice.

Drainage.

If you are planning a raised garden bed or planter box, drainage is imperative to ensure the plant roots do not get waterlogged. In some instance you will need a potting mix-type media high in organic matter. Always provide a layer of drainage material (gravel etc) at the bottom of your garden bed prior to the soil to improve drainage.

Nutrients.

The level of nutrients within your soil can influence the successful growth of your plants. Identify the nutrient needs of the plants/veges you are growing before choosing your soil. Soil with a moderate level of organic matter and fertilizers mixed in is a good start. You can always add more fertilizer topically, but if there is too much ‘punch’ in the soil, you cannot remove it and can lead to burning and dying plants. Remember, those plants will draw those nutrients out to assist growth, so you will need to add some nutrients to the soil at some stage.

Top Dressing.

The important thing when top dressing is to use a fine material with very little visible organic matter. The finer the material, the better it will permeate down into grass roots. Any sizeable matter will be left on the surface and can damage your mower (or surrounding windows!). Best to use a sand-based top dress for this reason.

Laying Turf.

When choosing an under-turf soil, you need to establish a balance between moisture retention and drainage so your new lawn can flourish. Once again, a moderate amount of organic matter and fertilizers can help establish your lawn. The roots from the turf slabs will need to strike into this soil to grow, so avoid any clay-heavy soils.

When it comes to choosing the right soil for the right job, it pays to do your research, establish the purpose and ask plenty of questions at your landscape outlet to ensure to indentify the best product for your needs.