How toxic is lawn fertilizer really?

If you want a nice dense lawn, you should apply lawn fertilizer several times a year. Many hobby gardeners wonder whether the products are poisonous or whether children and pets can then enter the areas safely. We clarify.

With three to four servings of lawn fertilizer per year, a lawn shows its best side. It starts as soon as the forsythia bloom in March / April. Long-term lawn fertilizers are recommended because they release their nutrients evenly over several months. A gift after the first mowing is ideal. A second portion of fertilizer is available at the end of June, optionally in August for heavily used areas. In the middle of October you should apply a potassium-rich autumn lawn fertilizer. It makes the grass hardy. The granulate can be distributed most evenly with a spreader.

A common question is: Is lawn fertilizer toxic to children playing or pets? When answering, one should first differentiate exactly what a lawn fertilizer is, because there are mineral lawn fertilizers, organic lawn fertilizers and those with special active substances against lawn weeds and / or moss.

Long-term mineral fertilizer

Purely mineral lawn fertilizers without additional additives against weeds or moss are about as toxic as table salt. With them, you should wait after fertilizing until the fertilizer pellets have completely sprinkled through the lawn and lie on the turf. Experience has shown that this is the case after thorough irrigation or a heavy rain shower. For safety, you can still wait for the next lawn cut before the fresh green becomes a playground again. Tip: In dry weather, irrigate the lawn for about 20 to 30 minutes immediately after applying a pure lawn fertilizer so that the fertilizer is well watered into the turf and can release its immediately effective nutrient components.

When used correctly, children and dogs can safely walk on a freshly fertilized lawn

Organic lawn fertilizer

With normal and proper use, a purely organic lawn fertilizer is also harmless to humans and animals and the lawn can be re-entered immediately after spreading. Organic lawn fertilizer, for example “Azet lawn fertilizer” from Neudorff, contains, according to the manufacturer, sterilized, organic and natural raw materials. A risk to children and pets is not expected because the manufacturer advertises on the packaging that the product is harmless. The fertilizer works as soon as its organic components are decomposed by microorganisms. Through this so-called mineralization, the plant nutrients are released and can be absorbed by the plant roots. Irrigation is not absolutely necessary because organic lawn fertilizer does not cause leaf burns, but it does accelerate the effect.

Problem case castor meal

Organic lawn fertilizers have been discredited in the past for containing castor meal. The nitrogen-rich press residues from castor oil production contain the highly toxic castor oil. The press cake must be heated to 80 degrees for at least 15 minutes before further processing as fertilizer or animal feed so that the toxin decomposes. Nevertheless, a few years ago, dogs that had eaten organic fertilizers showed severe signs of intoxication, sometimes even resulting in death. The reason is that individual batches of castor meal were apparently not heated long enough. It is also known that the animals react very sensitively to even the smallest residual amount of poison. For this reason, well-known brand manufacturers such as Oscorna and Neudorff have not used castor meal in their fertilizers for several years.

The miracle tree (castor bean communis) is popular with us as an ornamental plant. In India it is mainly grown for its oily but highly toxic seeds

In Switzerland, the use of castor bean meal as fertilizer was even prohibited by law around three years ago. If you are a dog owner and want to buy organic lawn fertilizer, you should carefully study the list of ingredients, especially for cheap products, and if in doubt, choose a branded product.

Lawn fertilizer with weed killer

Lawn fertilizers with weed killers contain special growth substances that penetrate through the roots and leaves into so-called dicotyledonous weeds, for example dandelions or plantain. Because they accelerate the growth of lawn weeds, they die. These herbicides have no effect on the monocotyledon grasses themselves.

If a fertilizer with weed killer is applied, the lawn should already be moist when used, in this case you should water beforehand, because the best effect is achieved if the weed killer sticks to the weeds for one to two days. After this period, you should water again if it has not rained in the meantime. As long as the herbicide is effective, neither children nor pets should enter the lawn.

Lawn fertilizer with moss killer

Lawn fertilizers with moss killers usually contain the active ingredient iron (II) sulfate. It burns the existing moss with its caustic effect. It is best to apply such lawn fertilizer on damp lawn shortly after mowing in order to reach the moss well. Water the lawn at the earliest two days after application and wait another two days until you mow it again. After 10 to 14 days you can use a rake or scarifier to remove the dead and now brown-black colored moss from the sward. The same applies here: keep children and pets away from freshly treated surfaces. The lawn should only be re-entered after thorough irrigation or heavy rain. Larger amounts of iron (II) sulfate can cause slight burns on the bare skin, since the iron, in combination with water, oxidizes to iron (III) ions and thereby releases acid. The iron (II) sulfate adhering to the shoes can also leave stubborn rust stains on stone slabs, wooden floors or clothing.

Another tip at the end: Store opened lawn fertilizer in a cool and dry place that is inaccessible to children and pets.

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