Following my article on fertilizing lawns, I wish to give you tips on the other possibilities for the yellowing grass, other than fertilizer burn. Fertilizer burn is easily identified, as it normally manifests itself after a broadcast of high Nitrogen containing plant food, and lessens with the amount of irrigation. The irrigation assists in the leaching of the soils, diverting the excesses to lower substrata.
Aeration is probably the most important exercise to performed on the lawn grass, for the following reason. Plants roots need oxygen, it is as simple as that. Aeration is the practice of mechanically managing the soil structure to increase subsurface breathing, increasing the oxygen supply to the root zone. It also aids in the drainage of soils to combat layering, and facilitates areas for the roots to grow. Roots do not grow in soil but rather in the spaces between the soil particles.
Compacting soils, reduces the air space between soil particles, as well as inhibiting good drainage. Drainage of moisture from the surface areas is greatly affected when this compaction occurs and what follows is that the soils become anaerobic (lack oxygen).
Anaerobic conditions, can best be described by the increase of anaerobiotic microbes which feed on organic matter. They acquire their oxygen by chemically removing it from sulphate compounds in the soil, giving rise to hydrogen sulphide gas. This gas is toxic to the roots, and has the odour of rotting eggs. Anaerobic soils are dark in colour and eventually turn black (the name black layering is associated with anaerobic soils.) Soils lacking oxygen curb the roots to breathing capacity, resulting in the deep roots dying, and a shortened root developing, and only surviving in the upper levels of the oxygenated soils. Shallow roots come with multiple problems, and if prompt action is not taken to aerate the soils, the result could be the total loss of the grass. Anaerobic soils can also drown the good microbes, as water that is unable to drain from the surface level, will asphyxiate the good microbes that require oxygen to survive.
Lack of good rooting, or short roots, inhibit their ability to supply enough moisture and nutrients to the crown of the grass to maximize growth. So the grass lacks the mechanism to supply enough moisture for transpiration during the hotter parts of the day, and scorching or hot spots develop. This appears as yellowing of the grass crown, and without cooling off with irrigation or spot syringing, can lead to the death of the grass.
The optimal remedy for combating these conditions, is to annually or bi-annually, spike the lawn, either with a spiked roller or with the use of a garden fork. This loosens the substrata and improves conditions for root growth. The deeper the root, the healthier the crown. If hot spots develop in the high season, spike the affected area and water well, ensuring the water drains into the soils. Remember do not to over water the area, encouraged the roots to grow and develop. I always use the analogy if you receive water at a certain faucet, you will always drink there, if the supply ceases, you seek another faucet. A root can be seen in the same light. If you continue to supply its daily requirements in the shallow soil area, why would it need to root deeper?
Soils contain millions of microbes, good and bad, and it is the soil preparation to encourage good microbial growth that must be the effort of your convictions.
Follow my articles, as I will continue to give tips for good lawn grasses, the pit falls to look for and many other solutions to minor problems.