ROCK DUST
What is it?
Rock dust is a powder made from finely ground up rocks; it is a by-product of rock crushing and polishing. It is usually a mixture of granite and basalt rocks, which are high in iron, boron, manganese, copper, zinc and molybdenum.
The benefit of having such a fine powder enables soil microbes and chemicals to break the minerals down, meaning faster availability for plants.
What does it do?
Rock dust replaces minerals which have been used up or leached from poor and overworked soils. Users of rock dust have noted the following benefits:
- Increased drought resistance of plants
- Better taste in fruit and vegetables
- Increased earthworm activity
- Increased resistance to disease and insect attack
- Produces sturdy vigorous growth
- Improves composts and mulches
How much do you need?
Rock dust is less soluble than artificial fertilisers and stays active in the soil for some time.
We recommend using twice a year only, at a rate of approx. 1cup (250mL) per 7m2. After 3 years of application, remineralisation need only be done every 3 years.
Over application can lead to increased soil alkalinity. Remember that trace elements are important, but plants only require a very tiny amount.
Rock dust works best in conjunction with good organic soil building, and can be added to compost piles and worm farms.
Precautions
Rock dust is a natural product and is not toxic. However, inhalation of fine dust over a prolonged period without using respiratory protection may cause silicosis. Avoid using in windy conditions, and use a dust mask when applying to protect from inhalation.
BENTONITE
What is it?
Bentonite is a type of clay believed to be formed from decomposed volcanic ash – made from the minerals Montmorillonite and Beidellite (just in case you really wanted to know!).
It is used in many industries for loads of different tasks – from sinking oil wells, to dam lining to kitty litter manufacture.
Essentially, it is of interest to gardeners due to its water holding ability. It is useful in binding soil particles together to create a crumb structure, particularly when used with gypsum which keeps the bentonite from forming a putty when wet.
Bentonite replaces products like ‘Wetta Soil’* when worked into the top 100mm of soil. Use at a rate of 1kg per 10m2 on course sandy soils, and ½ kg per 10m2 on finer soils or soils with a higher humus content.
*Note – we recommend ‘Sand Remedy’ is a pre-mixed product ready to use on your garden in place of soil wetting agents. It has gypsum and other minerals added for improved performance., and is much easier to use than bentonite on its own.
ZEOLITE
What is it?
Produced through volcanic activity, Zeolite is a very porous mineral used in industry as a filtering agent for water, as a stockfeed supplement and in horticulture as a soil additive.
Due to its porous nature, each particle has a large surface area, enabling what is known as ‘cation exchange’ to take place. This means that Zeolite can hold and exchange nutrients required by plants, making nutrients readily available.
It can be worked into the top 100mm of soil, or added to compost piles. Use at a ratio of:
- Sand 2.5kg/10m2
- Sandy loam 1 – 2kg/10m2
- Poor clay ½ kg/10m2
- Compost 10kg/m3
- Liquid manure/compost tea 1 handful/10L
- Potting mix 2 – 10% V/V
GYPSUM
What is it?
Otherwise known as hydrated calcium sulfate, Gypsum occurs as a saline evaporite mineral from ancient watercourses (similar to limestone). It is a major industrial mineral used in products from paper to paint, and also as a food additive.
Gardeners are interested in its applications as a clay breaker, helping to improve structure and increasing the infiltration of air and water through the soil. It also allows plant roots to penetrate, alleviating compaction.
Gypsum is pH neutral and is a useful source of calcium.
Application: Not all clay soils will respond to gypsum. To determine whether your soil will respond, drop a piece of dry clay approx. 6mm across into a glass of water. Do not move the glass – just leave it for an hour, then 24 hours. If it slowly disperses into the water, first forming a halo around the piece, it will respond to the addition of gypsum. The greater the cloudiness of the water and the more rapidly the clay disperses, the more gypsum will be required. If however after 24 hours the particle has done nothing at all in the water, it will be a waste of time adding gypsum.
Gypsum should be added at a rate of ½ - 1kg per m2, digging into the soil. It is also beneficial to add organic matter to continue to improve the soil structure.
DOLOMITE
What is it?
Otherwise known as calcium magnesium carbonate (calmag), Dolomite occurs as a type of limestone. It is widely used in industry and horticulture.
Dolomite will supply calcium and magnesium to your soil, and will increase the alkalinity (raise pH) of soils. Add small amounts of dolomite to worm farms and compost piles to counteract acidity.
PH testing is recommended to ascertain the correct amount of a liming agent to be applied to the soil. Adding dolomite to already alkaline soils will result in nutrient deficiencies in plants.
To raise the pH of the top 100mm of soil, use dolomite as below (grams/m2)
- Soil type
- Sand 150
- Loam 200
- Clay 300
It is better to add a little often rather than one large dose.
SULFUR
What is it?
Sulfur (the spelling has apparently been changed from sulphur!) occurs in craters of extinct volcanoes, and is produced in association with hot springs (that rotten egg gas smell!).
It is used in many products from match heads to rubber, and is useful in horticulture as a fungicide, insecticide and soil remedial agent.
Sulfur is used to raise the acidity (lower pH) of a soil. In extremely alkaline soils, it is more economical to use sulfur in addition to naturally acidic mulch such as pine needles or cedar shavings. Adding organic matter will naturally help to lower pH – but quite gradually.
To lower the pH of the top 100mm of soil use sulfur as below (grams/m2)
- Soil type
- Sand 30
- Loam 60
- Clay 80
Note that it will take some weeks to take effect. For a quicker result, use Chelated Iron which is mixed with water and applied with a watering can.
EPSOM SALT
(MAGNESIUM SULPHATE)
Magnesium is essential for photosynthesis in that it is an important element in chlorophyll production. Deficiency symptoms generally become evident in older leaves first and are indicated by a yellowing of leaf tissue between the veins, sometimes accompanied by orange tints. Affected plants deteriorate rapidly, loosing leaves and eventually dying.
If you suspect a magnesium deficiency, it is a good idea to conduct a pH test on the soil, as it can be a symptom of too alkaline conditions.
Application Rate:
Dissolve 10 grams (approx. 2 teaspoons) in each litre of water and apply liberally over soil around the root system. For plants showing severe deficiency symptoms, repeat this application every 4 weeks until symptoms ease.
POTASH
(Potassium Sulphate)
Potassium is one of the three ‘macronutrients’ essential for healthy plant growth. It is used in chlorophyll formation and plays an important part in strengthening cells and the movement of water throughout the plant. This strengthening effect helps prevent damage and disease and improves the quality of flowers, fruit and seeds.
Sulphate of Potash also contains sulphur.
Application Rate:
Wet: Use 5gms (approx. 1 heaped teaspoon) in 2 litres of water and apply liberally over soil and foliage. Repeat weekly for 3-4 weeks. Best applied in early morning or evening.
Dry: Apply at a rate of 20gms per square metre or 1kg per 50m2 and water thoroughly.
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Western Australian soils are some of the oldest in the world, and are extremely deficient in most of the essential nutrients we human animals need in our diet.