Black spots in the lawn: cause & help

A well-groomed one race is the figurehead for every garden. Sometimes black spots can blemish the lawn. The cause for this can be varied. More on this below.

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:

• damp - warm weather
• prolonged rainfall
• very high humidity
• Lack of nutrients in the soil
• Compaction of the soil
• bad and wrong lawn care over the year
• Soil in the acidic area

When the first fungi show up, immediate help is necessary to prevent further damage to the lawn. The following should be noted:

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

Possibly earth exchange

In the event of a larger, massive infestation and if the measures do not help, all that remains is to replace the soil on the affected areas. This will be

• affected area excavated 30 cm deep
• filled with new, fresh earth
• afterwards an overseeding carried out

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

Black roots

With this fungal disease, too, which attacks the roots of the grasses and discolors them from dark brown to black, black spots are then visible in the lawn. It is the so-called black-leggedness (Ophiobolus graminis). It mainly occurs on grasses with fine, delicate leaves. The disease can be recognized by the following features:

• Occurs in late summer and spring, depending on the weather
• initially yellow to orange spots on the lawn
• 5 to 10 cm in diameter
• then spots merge into one another
• a diameter of 1 m is possible
• eventually the roots are attacked
• these change color from brown to black

Black-leggedness has various causes and is also favored by a number of factors. These include:

• too calcareous soils
• Lack of nutrients in the soil
• long-lasting moisture
• also drought stress of the plants
• Soil in the acidic area
• 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. The gas exchange as well as the infiltration of the water in the soil is interrupted by a tight covering of the soil by this layer. The grass plants then literally suffocate. There are various causes for algae growth, such as:

• occurring mainly in the cooler season
• heavily compacted soil
• Nutritional deficiency
• low humus content
• mainly potassium deficiency
• weakened and patchy sward
• Moss and felt formation
• prolonged humidity and moderate temperatures or
• excessive watering with little drainage of the soil
• too deep cut and
• Shadows

This can very quickly lead to a so-called large "soil bloom" overnight. Simply drying out the algae layer is not enough, because the next time it rains, it would grow back again. As with the previously mentioned causes for the formation of black spots on the lawn, the following measures to combat and prevent are well suited.

Note: at Seaweed chemical agents are of no help. They can only be removed mechanically. It is important that the top layer of algae or The earth layer 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 correct lawn care and serve the health of the plants and ensure lush growth:

• adequate supply of nutrients
• balanced fertilization in spring and autumn
• in autumn use of potash-based fertilizer
• in the case of deficiency symptoms also fertilize in the summer months of June / July
• Optimize irrigation
• As a rule of thumb: 15 l water / m² every 4 to 7 days depending on the weather
• Verticulate the soil in spring, aerate if necessary
• this improves floor ventilation
• ideal time for this April to May
• if necessary, still 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
• Depth of cut not less than 4 cm
• Soil pH between 5.5 and 7.0 is ideal

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

Caution: acidic soil

If 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 to add carbonate of lime to the lawn. The procedure is as described below.

• Testing the pH
• commercially available test strips
• Mow the lawn as usual
• Scarify the area
• thereby better lime absorption
• then sprinkle with lime
• Use of a spreader would be ideal
• thereby even distribution
• then water thoroughly
• only fertilize after three to four weeks

Not only the grass plants are happy about the addition of lime, at the same time mushrooms, moss and weeds are prevented from growing. But never use quicklime, this kills pests in the soil like snail eggs, but at the same time all organic components in the soil burn.

Note: 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 on their own after a maximum of one week. They do not cause harm.

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