Why you should not want to use standardized pre-fabricated earth from the garden market …

DIY composting has many advantages. The most important reason is sure that you know exactly what is in your compost. Good compost is also very expensive, making composting on your own worth it  in just a short period of time.

In addition to saving money on the purchase, bought garden soil usually doesn’t have the same quality as self-produced compost and is (unfortunately) often mixed with harmful substances, as has been found out in a test of the magazine Öko-Test.

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Fertilization tailored to suit a market need requires soil analysis. Nevertheless, hobby gardeners like to use universal-typed fertilizers that claim to contain all important nutrients – but that also include heavy metals. Since many products are also declared inadequate in our test, we can only recommended 3 out of 20.

The test result of 20 products (Öko-Test)

Only the three mineral fertilizers by Obi, Toom and Compo passed our rigorous evaluation with an “outstanding”. They are followed by a wide midfield in which most products land because they add heavy metals into the soil and often still have faults in their declarations. Six fertilizers, all with organic content, are “poor” or even “unsatisfactory”.

Some fertilizers add more than three times the amount of heavy metal into the ground, as can be withdrawn over the course of a growing season. “In the course of time, this increases the heavy metal content of the products produced; thus, there is a risk of entry into the groundwater,” explains Professor Ewald Schnug, lecturer at the University of Technology of Braunschweig and President of the International Scientific Centre for Fertilizers (CIEC). Five fertilizer have a uranium content which is higher than the limit of 50 milligrams per kilogram of phosphate, which was recommended by the Federal Environment Agency. Uranium as well as cadmium passes as rock phosphate in the fertilizer. For years, it has been discussed whether there should be a legal limit for uranium in fertilizers, but so far, nothing has been done.

For the first time we have also depreciated fertilizers which add more than three times as much phosphate into the ground as can be taken from it. The background: Regulatory measurements have shown that in most gardens  there is enough phosphate, in some even too much. “If phosphate is washed out, it may contribute to the overfertilisation of waters,” says fertilizer expert Ewald Schnug. “We should be particularly economical with phosphate: It is obtained from fossil deposits that are slowly but surely running out, while simultaneously increasing the global demand for fertilizer.”

Since our garden fertilizer test in 2013, residues of perchlorate and chlorate have been found in several samples of fruits and vegetables. Both substances can inhibit, among other things, the inclusion of iodide into the thyroid gland. One possible source of contamination in food appears to be fertilizer. In fact, the laboratory commissioned by us pointed out chlorate in twelve fertilizers; six contained perchlorate. In the current state of science, the measured levels are too small too show harmful effects. Nevertheless, we evaluate them from, since the pollution is completely unnecessary.

Pesticides are registered with organic components in the fertilizer. Here, the laboratory found traces in nine cases; in two products, there were even six different types of pesticide. Polycyclic aromatic hydrocarbons, some of which are carcinogenic, were only found in conspicuous amounts in Beckmann products. None of the tested fertilizers showed signs of  E. coli or salmonella bacteria.

If hobby gardeners want to fertilize according to specific requirements, they have bad cards in most fertilizers – the discrepancy between what is claimed on the packaging and the actual measured content is just too big. We found deviations in the nutrient content of more than 50 percent, or more than one percentage point, in more than half of the products. Some fertilizers have been devalued because the manufacturers should have identified certain nutrients or heavy metals according to fertilizer ordinance but did not. The ASB Greenworld Garden Fertilizer Blue was particularly striking: The values for nitrogen and water-soluble phosphate differ  by more than two percentage points; the trace elements boron and zinc do not even reach ten percent of the values marked. Another problem with ready-bought soil is also the associated  destruction of bogs…


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