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Look at the packaging
Look for formal identification with company name, factory address, telephone number, fertiliser registration certificate, expiry date, date of production, certificate of conformity, etc. Look for authorised production (generally those authorised to produce have no factory of their own and no source of raw materials). Also, try not to buy those packaged in foreign languages.
Look at the colour
High-quality organic fertilisers should be dark brown to black in colour after a long period of high-temperature fermentation and maturation; poor-quality ones are usually lighter in colour.
Smell
Smell carefully if the fertiliser smells of ammonia, manure or sludge. Generally speaking, good quality organic fertiliser has a special sour smell due to thorough decomposition.
Water solubility method
Dissolve organic fertiliser in water and observe that poor quality fertiliser is evenly distributed with more impurities and sinks to the bottom; good quality water-soluble fertiliser is evenly distributed and has a saucy colour.
Hand twisting method
Take organic fertiliser and crush it back and forth with your thumb and forefinger. If there is a pinching sensation, there is sand or other impurities inside and it is likely to be poor quality fertiliser.
Do the test
Take a pot of flowers, grab a large handful of organic fertiliser and sprinkle it directly onto the rhizome of the flower and water it. Good organic fertiliser will gradually grow white mycelium and promote plant growth, while organic fertiliser of substandard quality will smother the seedlings and the plant will gradually wilt until it dies.
You can also leave a portion of the field application without this organic fertiliser and observe the performance of the plants. A good organic fertiliser will have a noticeable effect in terms of growth, yield and quality.