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Ash specific weight: wood and coal ash

Using wood and coal ash is an excellent way to improve soil structure, feed garden plants with necessary minerals and trace elements of natural origin without chemical fertilizers. The main thing to determine before taking such steps is what characteristics the soil has, which plants need feeding and which ash should be used accordingly.

What is the difference between wood and coal ash?

Gardeners most often use ash as a complex fertilizer, but depending on what burned, one or another type of ash will have a different chemical composition. There is no need to discuss the harm of ash left after burning garbage, plastic and other waste: it will not only fail to help, but can seriously harm plants. Wood ash, as well as ash from herbaceous residues, contains almost no chlorine, which is extremely useful for potatoes and berry crops, but it contains substances plants need, such as:

  • potassium,

  • phosphorus,

  • fluorine,

  • calcium,

  • iron,

  • sulfur,

  • zinc and others.

In ash, potassium and phosphorus are in the most convenient form for plant absorption, so it can be sprinkled on soil before deep plowing or added directly to the hole before planting. But this applies only to wood ash and ash from herbaceous residues, such as sunflower, potato tops, cereals and so on.

Coal ash is poor in potassium and phosphorus useful to plants, but it contains silicon oxides, which can significantly improve the composition and structure of heavy clay wet soils. Sulfur contained in coal ash forms sulfates, which leads to acidification rather than neutralization of soils. Therefore, coal ash is used on saline soils and is not used on acidic and sandy soils.

How much ash should be added?

For a large harvest, fertilizers should be applied correctly, understanding their effect on soil and plants. Regarding soil type, the main rules are:

  • The approximate application rate of wood ash depends on soil type and cultivated crops. Before regular application, it is better to consider soil acidity and recommendations for specific plants.

  • Wood and grass ash is suitable for any soil type except solonetzic soils; it reduces acidity and improves structure. Fertilization should be carried out no more than once every 2-4 years.

  • Ash is added to clay soils and loams in autumn before plowing, and to sandy and sandy-loam soils in spring.

  • Peat and shale ash is added to reduce soil acidity because it contains a large amount of lime. The rate is 650 g per 1 m2.

Use of coal ash

Low-quality coal contains a lot of sulfur, which can harm plants that do not need it, so such ash is better not used.

Because rainwater stagnates on alkaline soils, adding coal ash to alkaline soil will greatly worsen its condition, and the chlorine salts formed will harm plants. Good-quality coal ash can significantly improve clay soil.

Sulfur from coal ash is needed by:

  • onion and garlic,

  • cabbage and horseradish,

  • radish and swede.

Substance nameDensity, g/cm3Specific weight, kg/m3Bulk weight, t/m3
Wood ash weight0.4-0.5400-5000.4-0.5
Coal ash weight0.6-1.45600-14500.6-1.45

Specific weight, density, of ash

For small amounts of fertilizer, small measures are convenient, for example:

  • 1 heaped tablespoon of ash contains about 7 g, and a teaspoon contains 2-3 g,

  • a matchbox contains 10 g,

  • a 250 ml glass contains 100 g of ash,

  • a 0.5 l jar contains 250 g,

  • a liter jar contains about 0.5 kg.

Frequently Asked Questions

Can the density of ash be used for precise calculations?

The density and weight values for ash in this article are reference values. They are suitable for preliminary estimates, but design, construction, production and other critical calculations should be checked against standards, material datasheets or measurement results.

Why can the actual weight of ash differ from the table?

The actual weight of ash depends on composition, moisture, temperature, porosity, fraction size, material grade and measurement conditions. Because of this, real values may differ from the average table data.

How do you calculate the mass of ash from density?

For an approximate calculation, use the formula: mass = density × volume. If the density of ash is given in kg/m³ and the volume is in m³, the result will be in kilograms.