As the mowing season begins in earnest it’s time to address that age old debate, whether it is better to remove clippings after mowing or to leave them on the lawn. This is something that divides the amateur and professional alike so it is helpful to look at the advantages and disadvantages of mulching.
Advantages of mulching
Nutrition is returned to the soil from the cut leaves.
No need to dispose of clippings.
Less time and labour.
Disadvantages of mulching
Too thick a layer can deprive the grass sunlight and the ability to grow.
Clippings raise humidity levels within the canopy potentially encouraging fungal disease.
Organic material can contribute to thatch.
Weeds seeds can be redistributed to the soil.
Let’s address these points in turn.
Nutrition is returned to the soil
The soil is a complex ecosystem, where dead and decomposing plant and animal matter feed countless micro-organisms that in turn facilitate plant growth. Allowing plant material back into the soil is very important for maintaining this ecosystem. Every blade of grass contains nutrients drawn from the soil and when the lawn is mown these nutrients are removed. Whilst not replacing everything that is taken, mulching can help replenish these valuable nutrients. Note that if your lawn is being regularly fertilised then this requirement reduces somewhat although the clippings are still very useful for their carbon content.
No need to dispose of the clippings/less time and labour This is self-explanatory – leaving the clippings makes your life easier, and who doesn’t want that?
Clippings can deprive the grass sunlight
Grass is a plant that grows through the process of photosynthesis – meaning that it is completely dependent upon light. Deprived of sunlight it will ultimately die. Certainly grass is very hardy and will recover from most things (think of the patch a tent leaves behind after camping) but any reduction in sunlight will have a weakening effect that will in the long run detract from your lawn’s potential. The key here therefore is quantity, light clippings will have negligible effect, and heavy clippings will have a profound effect.
Clippings will raise humidity levels and encourage fungal disease
As with sunlight, grass also needs water to survive. That water however needs to be in the soil and not above it. Moisture in the soil aids growth, moisture in the canopy does not. In the summer when soil moisture levels decline and the grass plant weakens, excess moisture in the canopy can encourage fungal pathogens such as Red Thread that thrive on the already weakened grass and damage it further. Again though this is a matter of volume, light clippings will dry rapidly in the sunlight, heavy clippings will hold the moisture far longer.
Clippings can contribute to thatch
Any organic material that ends up in the soil will start to undergo a process of decomposition. The rate of this decomposition depends on factors such as oxygen content, temperature and compaction. In circumstances where incomplete decomposition takes place a spongy layer of organic material can accumulate in top layers of the soil, this is called thatch. Thatch in anything other than moderate quantities is the enemy of the lawn as it prevents both water and nutrient from reaching the grass roots, it stifles air flow and locks in humidity, providing a breeding ground for moss and fungal disease. The devil is in the detail here though as generally it is the more fibrous parts of the grass plant that contribute to thatch as these are slower to break down. In practice light mowing that only removes the leaf tips is unlikely to contribute significantly to thatch formation.
Weeds seeds can be redistributed to the soil
Some weeds such as the lawn enthusiast’s nemesis, Speedwell are small enough to flower and seed under the mower blade and then reproduce when their seed (or clippings of their own structure) are spread about by the mower blades. Removing the clippings is no guarantee that this will not occur but it seems highly likely that it will reduce the likelihood.
So what is our advice?
Well if you mow your lawn regularly (more than once a week) and only a few mm of grass tips are removed each time then mulching is highly recommended as you get all the benefits with very little risk. This is where robot lawnmowers excel since they take regular mowing to the nth degree and deposit only the very lightest clippings. If weeds are a significant problem and you still wish to mulch then a professional lawn care program will help. It is fair to say however that regular mowing contributes to a healthier lawn which in turns naturally helps to combat the spread of weeds.
If however you mow less often or remove a significant proportion of leaf then we would recommend against mulching, particularly if your lawn is being regularly nourished by a lawn care program. That does not mean that the clippings should be disposed of as they have their place on a balanced compost heap or can make useful mulch underneath a hedge - in nature nothing goes to waste. Regularly supplementing the lawn with products such as liquid seaweed and humic acid can also help compensate for the nutrients removed
For further lawn care advice or to check out any of our services that include fertilisation, weed control, soil improvers, aeration, root stimulators, wetting agents and scarification please visit our website at www.hamsphirelawncraft.com.