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A beautifully manicured lawn is the hallmark of any garden. Sometimes it can happen that black spots disfigure the lawn. The cause of this can be various. More on that below.

In a nutshell

  • Fungi and algae: cause of discolouration
  • Poor lawn care is to blame for infestations
  • Scarifying and aerating an absolute must
  • Combat stains mechanically

Mushrooms sprout at night

One cause of black spots or even large areas of black discoloration on the lawn can be the presence of fungi. Of course, these are not mushrooms that are intended for consumption, but these damage the lawn. They sprout very quickly overnight, their growth is favored by various factors such as:

Fungi cause black spots in the lawn
  • humid - warm weather
  • prolonged rainfall
  • very high humidity
  • nutrient deficiency in the soil
  • soil compaction
  • poor and incorrect lawn care throughout the year
  • acidic soil

When the first fungi appear, immediate help is needed to prevent further damage to the lawn. The following should be observed:

  • never mow the mushrooms
  • all cut out by hand
  • thereby preventing the spread of fungal spores
  • do not mow infested areas
  • mow remaining area every seven days
  • Cutting depth 3 to 5 cm
  • dispose of clippings immediately
  • not on the compost, spreading of spores
  • put in the trash

Possibly earth exchange

In the event of a larger, massive infestation and if the measures do not help, the only option left is to replace the soil on the affected areas. this will

  • affected area dug 30 cm deep
  • filled with new, fresh soil
  • followed by reseeding

Again, care must be taken to ensure that the old soil is no longer used in the garden. This should also be disposed of in the residual waste.

Black Roots

Black spots are also visible in the lawn with this fungal disease, which attacks the roots of the grass and turns them dark brown to black. This is the so-called blackleg (Ophiobolus graminis). It mainly occurs in grasses with fine, tender leaves. The disease can be recognized by the following characteristics:

  • Occurrence in late summer and spring, depending on the weather
  • initially yellow to orange patches on the lawn
  • Diameter 5 to 10 cm
  • then spots merge into each other
  • a diameter of 1 m is possible
  • Finally, the roots are infested
  • these change color from brown to black

Blackleg has various causes and is also favored by a number of factors. These include, among others:

  • too calcareous soils
  • nutrient deficiency in the soil
  • long-lasting moisture
  • also drought stress of the plants
  • acidic soil
  • low drainage of the soil

Algae as the culprit

Blue-green algae can also be responsible for black spots on the lawn. These become visible as black-green to black, greasy and slippery deposits on the grass plants. By covering the ground tightly with this covering, the gas exchange and the infiltration of water into the ground are interrupted. The grass plants then literally suffocate. There are various reasons for algae growth, such as:

Blue-green algae can cause black spots in the lawn
  • occurring mainly in the cooler season
  • heavily compacted soil
  • nutrient deficiency
  • low humus content
  • mainly potassium deficiency
  • weakened and patchy turf
  • Moss and felt formation
  • prolonged humidity and moderate temperatures or
  • excessive watering with low drainage of the soil
  • too deep cut and
  • shaded areas

A so-called large “soil bloom” can occur very quickly overnight. Simply drying out the algae layer is not sufficient, because the next time it rains, it will grow back again. As with the previously mentioned causes of the formation of black spots on the lawn, the following measures are well suited to combating and preventing them.

Notice: With algae, chemical agents are of no help. They can only be removed mechanically. It is important that the top layer of algae or soil is completely removed.

Combat and prevent

Black spots on the lawn can be combated in a targeted manner. At the same time, the following measures should also be used to prevent any lawn diseases. These are part of proper lawn care and serve the health of the plants and ensure lush growth:

  • adequate nutrient supply
  • balanced fertilization in spring and autumn
  • in the fall, use of fertilizers with an emphasis on potash
  • additionally fertilize in the summer months of June/July in the event of deficiency symptoms
  • Optimize irrigation
  • the rule of thumb is: 15 l of water/m² every 4 to 7 days depending on the weather
  • Scarify soil in spring, aerate if necessary
  • this improves soil aeration
  • ideal time for April to May
  • if necessary also possible in autumn
  • then sand the lawn with fine-grain quartz sand
  • Rule of thumb: half a bucket per square meter, distribute well
  • immediate reseeding if there are gaps
  • regular mowing
  • Cutting depth not lower than 4 cm
  • Soil pH between 5.5 and 7.0 is ideal

Notice: The sand makes the soil surface more coarse-pored and thus more permeable to air and water. Waterlogging is avoided and the floor can dry better.

Caution: acidic soil

When the pH of the lawn falls below 5.5, the soil is said to be acidic. This is not beneficial for growth, nutrients can no longer be absorbed, and the growth of fungi and algae is also promoted. The only remedy here is a dose of carbonate of lime on the lawn. The procedure is as described below.

  • pH testing
  • commercially available test strips
  • Mow the lawn as usual
  • scarify the area
  • thus better absorption of lime
  • then spread lime
  • the ideal would be to use a spreader
  • thus even distribution
  • then water thoroughly
  • only fertilize after three to four weeks

Not only the grass plants are happy about a lime application, at the same time fungi, moss and weeds are prevented from growing. But never use burnt lime, this kills pests in the soil such as snail eggs, but at the same time all organic components in the soil are burned.

Notice: Slime molds (Mycetozoa or Eumycetozoa) can also cause black, greasy spots on the grass in warm, humid weather and compacted soil in the summer months. They disappear by themselves after a maximum of one week. They do no harm.

frequently asked Questions

Are fungicides recommended against fungi and algae?

No. For one thing, there are no chemical agents against algae on lawns. On the other hand, such agents are not permitted against fungi, mainly for cap fungus species. In addition, the use of fungicides and herbicides would only upset the biological balance in the garden and is extremely harmful to the environment. Pets and useful garden dwellers can also be harmed.

Does mulching help against fungi in the lawn?

In general, mulching with clippings is beneficial for lawns. The nutrients remain in the soil and can be reused. Furthermore, the activity of the microorganisms living in the soil is stimulated and the turf becomes denser. Mushrooms, weeds and moss then have a harder time. However, it then has to be mowed weekly. The grass must be dry and free of any organic matter.

Why do mushrooms often grow on lawns?

It is well known that all fungi love moisture, including those found in lawns. The reason for the growth is, among other things, a green area that is too moist. Too rainy weather, but also excessive watering can be to blame. This creates waterlogging and good growth conditions for fungi and algae, which then form black spots on the lawn. However, other causes should also be taken into account.

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