Fertiliser Guide–Nutrients,Properties And When To Use

This is a concise guide to the main types of straight fertilisers in use. The main points covered are:

  1. Fertiliser and main nutrient supplied
  2. Properties
  3. When and how much to use

Basic slag


  • Phosphates
  • 8-16% P205 (insol)
  • Slow acting inorganic. Active ingredient is calcium silicophosphate which is an insoluble material; slow acting and long lasting. Its lime content makes it a useful fertiliser for acid soils that are also low in phosphates
  • Autumn or winter open ground 8 oz per square yard before sowing or planting. Not to be used with lime

Bone flour


  • Phosphates 27-28% P205 (insol) 1% N Concentrated organic.
  • Active ingredient calcium phosphate which is insoluble; being very finely ground it is fairly quick acting Has a very small amount of nitrogen.
  • Useful for keeping home-made mixtures of fertilisers in dry condition Open ground autumn or winter 4 oz per square yard before sowing or planting.
  • Can be used in potting composts

Bone meal


  • 20-25% P205 3-5% N
  • Concentrated organic. Active ingredient calcium phosphate, insoluble but releases its phosphates slowly over a long period
  • Has a useful content of nitrogen which works quickly Open ground autumn or winter 4 oz per square yard before sowing or planting.
  • Can be used in potting composts 4 oz per bushel

Dried blood


  • Nitrogen 7-14% N
  • Concentrated organic. Quick acting especially in warm, moist soils and it is one of the most rapid of organic fertilisers.
  • There is a fully soluble form that can be dissolved in water and used as a liquid feed Used as a top-dressing mainly for greenhouse plants throughout season. 2-3 oz per square yard

Hoof and horn meal


  • Nitrogen
  • 7-13% N
  • Concentrated organic. Acts fairly quickly in warm moist soils but long lasting.
  • Available in a number of grades: Fine grade inch to dust as used in John lnnes Base Fertiliser, acts quickly but hoof parings and other coarse grades very slowly
  • Open ground and greenhouse borders 4-6 oz per square yard John Innes Base Fertiliser for potting composts. Coarse grades are best for perennial borders

Magnesium sulphate

  • 10% Mg
  • Inorganic
  • Coarsely crystalline soluble material. Tends to cake on storage. Used only where magnesium is lacking
  • Can be used at 1-2 oz per square yard or applied as a leaf spray oz per gallon of water

Meat and bone meal

  • Nitrogen and Phosphates
  • 4-6% N / 12-14% P205 (insol)
  • A good organic fertiliser for general use, which comes from waste meat, offals and condemned carcasses from slaughter houses. The mixture is steamed under pressure to remove fat and then dried at a high temperature to kill disease organisms.
  • The nitrogen and phosphate content varies. The higher the content of bone the more phosphates it contains. These are insoluble in water and only slowly available to plants. The nitrogen portion works quickly in warm moist soils
  • Autumn or winter. Fork into open ground, 4 oz per square yard before sowing or planting.
  • Safe to use in greenhouse borders and can be used in composts.
  • Should be mixed with sulphate of potash to give a balanced feed.

Nitrate of soda

  • Nitrogen
  • 16% N
  • All the nitrogen is present as a soluble nitrate and is immediately available to plants as soon as it has dissolved in the soil moisture. If watered in its effects will be seen in a few days.
  • It can destroy the crumb structure of some soils if large dressings are given too frequently
  • Spring and summer as a top dressing for green crops or plants that are growing very slowly after cold wet weather.
  • Half Oz per square yard at intervals of several weeks


  • Nitrogen
  • 21% N
  • A mixture of ammonium nitrate and chalk. It has some nitrate for immediate action and the ammonia comes into play somewhat later. The chalk present largely balances any loss of lime from the soil that may be caused by the ammonia part of this fertiliser. Its granular form makes it easy to spread
  • It becomes pasty if left in air for long periods.
  • The chalk content is so small that it does not make the soil alkaline
  • Spring and summer top dressing for many crops including lawns 1/2  oz per square yard at intervals of several weeks

Potash nitrate

  • Nitrogen/Potash 15% N 10% K20
  • A mixed nitrate of sodium and potassium. Acts quickly. Useful two-in-one fertiliser for supplying potash as well as nitrogen in early spring crops that would make too much soft growth if nitrogen only was given.
  • Useful for soils that are low in potash as well as nitrogen
  • Spring and summer, used as a top dressing for many crops
  • Apply 1-2 oz per square yard direct to the soil or mix 1 teaspoonful to one gallon of water two or three times during the growing period

Potassium nitrate

  • Nitrogen Potassium
  • N 12-14% K20 44-46%
  • This is a pure concentrated fertiliser that is used mainly in liquid feeds.
  • It is suitable for all greenhouse plants when dissolved in water
  • Mix 1 teaspoonful to one gallon of water and apply regularly as a liquid feed

Sulphate of ammonia

  • Nitrogen
  • 20.6% N
  • When applied to the soil the ammonia part is held by the clay and organic matter and is preserved from immediate loss during wet weather.
  • When the soil is warm enough the ammonia is quickly turned into nitrate by soil bacteria. But this conversion is very slow when the soil temperature drops below about 42°F (5°C)
  • When mixed with sand is called lawn sand.
  • Repeated heavy dressings may make the soil too acid for good growth but acid forming property is an advantage to chalky soils
  • Spring and summer direct to soil at I-1 oz per square yard. Or dissolve 1 teaspoonful in 1 gallon of water and use as liquid feed
  • Often mixed with superphosphate and sulphate of potash but do not mix with lime

Superphosphate of lime

  • Phosphate
  • 18-19% P205
  • This contains phosphates that are soluble in water and it acts quickly, being particularly suitable for seed beds and root crops.
  • It does not supply lime in spite of its name
  • Can be used at any time at rate of 1-2 oz per square yard before sowing or planting.
  • Used in John Innes Base Fertiliser to supply phosphates

Sulphate of potash

  • Potash
  • 50% K20
  • The best form of potash for most garden plants. Acts quickly. It is held by the clay and humus in soils until required by plants.
  • To correct potash deficiency quickly dissolve 1 oz in a gallon of water and wet soil thoroughly.
  • Always use for gooseberries, red currants and other soft fruits in preference to muriate of potash
  • Generally used in combination with other fertilisers and raked in before sowing or planting at any time of the year 1-1 oz per square yard

Sulphate of iron

  • Iron
  • When one part is mixed with three parts of sulphate of ammonia and sand it will kill moss, clover and broad-leaved weeds in lawns and freshen up the colour.
  • Can be used for correcting iron deficiency in acid soils, but is ineffective for this purpose in limey soils.
  • It should be powdered finely
  • Used in lawn sands


  • Nitrogen 38% N
  • Synthetic organic. A combination of urea and formaldehyde which is sold under a trade name—which in spite of its high analysis, will not burn plants.
  • Although mainly insoluble in water its nitrogen is gradually converted by soil bacteria to a form which is available to plants, and will feed plants continually for several months from one application. It is non-corrosive and will not rust fertiliser spreaders and other equipment
  • Use at any time of year before sowing or planting in the open or in the greenhouse.
  • The slow release action of this fertiliser encourages durable healthy turf and reduces the danger of burning the lawn 1-2 oz per square yard.
  • Can be used in place of hoof and-horn in soilless composts 1 part by weight of Urea-form 2 parts by weight of super-phosphate 1 part by weight of sulphate of potash

Wood ashes

  • Potash
  • Freshly made wood ashes contain potassium carbonate, which is soon washed out by rain water unless the ashes are protected.
  • Ashes from prunings and other young plant material are richer in potash than old stumps. Heavy dressings may cake the surface and spoil the tilth of clayey soils.
  • Do not give large dressings to chalky soils because ashes may make them more alkaline
  • Autumn or winter in open ground. 4-8 oz per square yard well ahead of sowing or planting


  • Nitrogen 1-7% N
  • Contains nitrogen mainly as ammonium sulphate and therefore acts rapidly.
  • Since fresh soot contains substances harmful to plants it is best left under cover for three months before use.
  • Light and fluffy soot contains more nitrogen than the heavy dense type. Most soots supply useful amounts of trace elements
  • Spread over soil after digging and then rake in at rate of 4-6 oz per square yard.
  • Can be used as top dressing for brassicas at the same rate

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