Tofully understand why it is necessary to feed a lawn, and whenyou should, it is helpful to know a little about grasses asplants. All plants use their leaves in the food assimilationprocess which then keeps them healthy most of the time andare able to go through life without too much help or hindrancefrom human beings.
The lawn in the image, never gets fed - and rarely watered! It is subjected to the public walking over it week in week out!
If you strip the leaves off a perennial plant, they will normally re grow but a little bit smaller and weaker. If you keep taking the leaves off, the plant will eventually weaken and die. No matter how good the soil below is, if the plant cannot turn soil chemicals into the food that it requires, it will starve.
Leaves are responsible for assimilation of soil chemicals into life-giving nutrients to feed the whole plant. The stem, roots, flower buds and new leaves; all are dependent upon those life-supporting leaves.
As an analogy, if you place a sheet of black plastic over a patch of weeds, they will eventually die even the roots of stubborn weed plants such as nettles and ground elder. The sheet will stop the sunlight, which the leaves need to carry out their work of photosynthesis; they will firstly turn yellow before dying, along with the rest of the weed plant!
The lawn is made up of thousands of individual plants. It is not a single entity in itself! If you buy a 'turf' you are purchasing a patch of lawn which consist of several thousand plants!
When grasses are used in the lawn, they suffer all manner of abuse from gardeners, who would not dream of treating other plants in the same way! For instance, we do not prune our shrubs every week, nor cut down our perennials or annuals on a regular basis. But, we need to do this with our lawns (grass plants) to keep them tidy, accessible and under control. We do this without too much thought as to what we are doing to them as plants!
This regular pruning of grasses in the lawn, results in both the food reserves and food-making properties of the foliage being removed from the plants your lawn grasses!
It is a fact that if you allow your grass to grow a little longer even with a regular trim it will normally stay greener, without too much additional help by way of fertilisers. This is because you are then leaving a good percentage of the foliage intact even if you have clipped its wings a little! It can carry its work albeit in a reduced manner! So now you will have grass that can take care of its feed requirements in a reasonably normal manner. It will reward you by staying greener even if not quite the artificial lush green of a fertilised lawns.
A lawn allowed to grow in this way, will have a much healthier grasses than a lawn of artificially fed grasses with feed which has a high proportion of Nitrogen. The high Nitrogen level is necessary to compensate for the lack of foliage which is essential for normal health!
I would argue with no proof that allowing the grass plants to grow as normally as possible, will ultimately strengthens them as whole plants. One then has to ponder whether there is a need for supplementary feeding with a high Potash Fertiliser to help the roots get through the winter!
In my days as a public park manager, responsible for a few hundred acres of grass which varied from bowling greens through to housing estate verges, I never recall feeding any grasses other than the well-clipped sports areas. Financial cutbacks meant the end of autumn feed on the sports turf also, but I never saw any evidence of grasses dying through the winter, or even getting a better start to life in the spring!
Yes, lawns require special form of maintenance including aeration in some instances, and top-dressing also. But it is hard to justify the habitual feeding regime advocated as being essential. But then I am not in the chemicals industry!