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Grow Better Gardens - How to Improve + Fertilise Your Soils

Fertilisers can play an important part in producing healthy plants but can also cause significant environmental damage so should be used carefully. There are natural and artificial fertilisers, each with varied characteristics. The type of fertiliser you use depends on the particular plants you have in your garden, the means in which the fertiliser is applied and your preference for natural versus chemical.

Ways of Fertilising

  • Using soil improvers to help change the structure of the soil and provide nutrients to the plants

  • Applying fertiliser directly to your plants to encourage growth, flowering and fruiting

Fertilising Natives

Many Australian plants grow naturally in soils that are low in nutrients and can suffer from strong chemical fertilisers or those that are high in phosphorus.   Natives prefer the use of soil improvers for soil and plant health.  As a general rule, stick with a slow-release fertiliser in Spring or when planting, that contains less than 3% Phosphorus.

Depending on which species you plant, topping up Rock Dusts, a dose of Sulphate of Potash (high in potassium) or a handful of Blood and Bone will probably be all your native garden needs for the year.

Types of Fertilising

Slow-release fertilisers

The easiest and safest way to fertilise.  Many of these only become active when the soil is above a certain temperature or moisture level, so plants absorb and use them only when they are actively growing and need nutrients most. Most slow-release fertilisers contain all the required elements for healthy plant growth and flowering

Soluble fertilisers

These are often used to provide a quick burst of nutrients to plants, and will then leach out of the soil quickly. This can become expensive and time-consuming as you need to repeat applications. Nutrients leached from this type of fertiliser can cause algal problems in nearby waterways if overused. These chemical fertilisers are generally used on annuals for fast leaf and flower growth.

Artificial Fertilisers

Conventional fertilisers feed your plants with three important macronutrients that are released directly to the plant from soluble salts:

  • Nitrogen            promotes leaf growth
  • Potassium         strengthens roots and stems and gives flowers their colours
  • Phosphorus      encourages fruit development and fertile seed

Plants absorb these and grow quickly but tend to suffer from micro-nutrient deficiencies that make them susceptible to pests and diseases.  There is also more likelihood of plants suffering water stress and have difficulty during dry spells as root systems are underdeveloped.  This is because the macro-nutrients are so readily available there is no need for root systems to forage and develop in the process.

Though chemical fertilisers do improve plant growth, there are many side effects including damaging the soil biomass, fertility and structure; contamination of waterways and groundwater through unused chemical salts leaching or washing off, and the creation of soil toxicity when nutrient elements become out of balance. These negatives far outweigh the positives of using artificial fertiliser.

Natural Soil Improvers

These are natural products that contain micronutrients that undergo a biological process to convert those nutrients into an available form readily released from the soil for absorption by plants as they require.

Cow or sheep manures, planting or mushroom compost, worm castings, green liquid fertiliser, seaweed extract, blood and bone and wood ash, Basalt Rock Dust and Alroc mineral fertilisers can all be used as soil improvers.  Turn these through the soil at planting time or top-dress with these in Spring to provide extra nutrients for new leaf growth.  Each product serves a different purpose and not all offer the same benefits but on the whole soil improvement does the following:

  • improve soil structure
  • increase levels of organic matter and humus in the soil
  •  improve moisture absorption and retention
  •  increase microbial and worm activity, thus aerating the soil for better root growth
  •  make nutrients available to the plants in small, manageable doses
  •  reduce watering costs and time once plants are established
  • helps counter the effects of soil acidity
  • helps reduce erosion
  • improves resistance to fungus, pests and disease
  • produces plants with an extensive feeder root system
  • reduces reliance on artificial fertilisers
  • protects waterways from soluble salts
  • protects people from chemical exposure
  • saves input costs
  • are sustainable into the future


Remineralising soils with products like ‘Basalt Rock Dust’ or ‘Alroc mineral fertilisers’ are environmentally sensitive ways of putting essential minerals back into the soil and also reduce the need for artificial fertilisers. They are an excellent and inexpensive long term remineralisation solution which adds elements to the soil biology and can be spread over your whole property.  These rock dusts mixed with compost have a dramatic effect on crop yields and significant impact on the health of garden plants and soil profile.

Alroc is a blend of volcanic Basalt, Granite, Dolomite, Bentonite, Rock Phosphate, Rock Potash and Bio Coal Fines, that slowly release a complete spectrum of minerals and trace elements into the soil.

Micro-organisms decompose rock dust from the surface of tiny Alroc particles and combine this with organic matter to form humus.  The rejuvenated soil supports a huge variety of soil organisms, some of which capture nitrogen from the air and make it available to the plants.  Plants grow nutrient-rich and can withstand pest attacks and disease much better.  Plants are also more capable of withstanding dry spells as they develop an extensive feeder root system.

Alroc uses a natural renewable energy source by utilising soil organisms to process nutrients for plants.  Remineralising soils offers all the benefits of soil improvement.

More information is available at and from Schmidt Quarries Queanbeyan.