How Does Mowing Trigger Grass Tillering? What the Research Shows
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How does mowing trigger grass tillering? Tillers are the shoots a grass plant produces from its buds, and removing the top of the plant can set more of them growing. Two research studies explain the mechanism. One studies trimming of bermudagrass, a turfgrass, and the other studies clipping of a forage grass to simulate grazing. Neither study tests a lawn mower directly, so the steps below separate what the studies measured from what they did not.
Quick answer
- Trimming has been found to induce tillering in turfgrass, and the bermudagrass study reports an increase in the number of tillers in the main stem after trimming.
- Lower buds are normally inhibited by the growing tip of the main stem, a pattern the source calls apical dominance.
- Trimming changes cytokinin and sucrose content, and it causes a rapid hydrogen peroxide burst in the leaves of new tillers and stolon buds.
- The source describes tiller initiation and elongation as an energy-consuming process.
What a tiller is
The bermudagrass study starts from the structure of the grass. Tillering or branching pattern plays a significant role in determining the structure and diversity of grass, and trimming has been found to induce tillering in turfgrass. The study describes the process as one that begins with the emergence of an axillary bud, originating from the axillary meristem located at the leaf axil.
The forage grass study describes the same growth form in clonal terms. The tillering response to grazing is one of the major mechanisms conferring plant resilience to herbivory, especially for clonal plants. Its counts separate the buds, the juvenile tillers, and the tillers, which gives a way to track how the plant rebuilds after damage. The numbers of tillers, juvenile tillers, and buds at the tiller nodes per tussock were counted in that study.
The first step: releasing held buds
Grass buds do not all grow at once. Apical dominance is a well-recognized phenomenon in which the growth of lower axillary buds is inhibited by the actively growing tip of the main stem. The bermudagrass study builds its work on this idea, and it says that regular and proper trimming can suppress the apical dominance of turfgrass, maintain a level lawn, and foster grass branching.
The study found that trimming acts on the buds at the nodes. Trimming stimulated the outgrowth of tiller buds located at the morphologically upper 1st, 2nd, and 3rd nodes of the stolon, with the most significant effect observed at the 1st node. In the experiment, the intact stolons showed no significant change in the length of their tiller buds. After trimming, the buds showed an S-shaped growth pattern.
The forage grass study looked at the same process from the side of damage. Resprouting from bud banks is one of the major mechanisms for plant compensatory growth after being grazed. In the forage grass, the number of tillers significantly decreased as simulated grazing increased, and the effect weakened with the prolonged recovery growth time.
The second step: sugar and cytokinin
The bermudagrass study tracked two signals. This effect is accompanied by spatial-temporal changes in cytokinin and sucrose content, as well as relevant gene expression in axillary buds. The source notes that cytokinin exerts its effects by directly entering the bud and promoting bud outgrowth.
Sugar also matters. According to the nutritional hypothesis, the competition for sugars between the apical meristem and axillary meristem plays a vital role in maintaining apical dominance. The source therefore links sugar supply to the control of the lower buds, which is the same control that trimming changes.
The study also measured the reserves in the new shoots. The partial trimming of new-born tillers results in an increase in sucrose and starch reserves in their leaves, which can be attributed to the enhanced photosynthesis capacity. The study therefore reports higher sugar and starch in the trimmed new tillers, with photosynthesis as the attributed cause.
The third step: a hydrogen peroxide signal
The bermudagrass study found a signal that appears soon after cutting. Trimming promotes a rapid H 2 O 2 burst in the leaves of new-born tillers and axillary stolon buds. The study then tested the molecule directly by applying it to plants after trimming.
The result was a clear increase in tillers. Exogenous application of H 2 O 2 significantly increases the number of tillers after trimming by affecting the expression of cytokinin-related genes, bolstering photosynthesis potential, energy reserves and antioxidant enzyme activity. The study concludes that both endogenous production and exogenous addition of H 2 O 2 enhance the inductive effects of trimming on the tillering process in bermudagrass.
Tillers need energy to form. The source describes this directly: tiller initiation and elongation is an energy-consuming process. That is why the energy reserves and photosynthesis measures in the same study are relevant to the answer.
Why cutting does not always add tillers
The forage grass study shows that the response depends on how hard the plant is cut. Four different clipping severities were used at the jointing stage and flowering stage to study the effect of simulated grazing. The grazing severities were set as control (unclipping), light (clipping with a stubble height of 15 cm), medium (clipping with a stubble height of 10 cm), and heavy (clipping with a stubble height of 5 cm). The number of tillers significantly decreased with the increase in simulated grazing.
The forage grass study reports that the bud and tiller responses were not the same. The bud number mainly showed over-compensation, the juvenile tiller number showed complete compensation, and the tiller number showed under-compensation at 1 and 3 weeks after recovery growth. The source also notes that most studies indicated that grazing would reduce the bud number due to promoting the production of tiller from bud.
The study also reports that different grazing severities in the jointing stage could promote the output of tillers with matter production capacity from vegetative reproduction modules. That result is specific to the jointing stage. In the flowering stage, the study says the tiller number showed under-compensation at 7 weeks after recovery growth, so timing changes the outcome.
What we could not verify
Neither study tests a lawn mower. The bermudagrass study uses trimming on stolons and stems, and the forage grass study uses clipping at fixed stubble heights to simulate grazing. The sources do not compare a mower blade with a trimmer, and they do not give the cut height a homeowner should use for a lawn.
What the sources do not say
The sources do not give a cutting schedule for any lawn. They do not measure how often a lawn should be mowed to keep tillers forming. The bermudagrass study recommends trimming the grass to maximize its tiller capacity, and it says this is for bermudagrass lawns. It does not give a height or interval for other grass types.
Frequently asked questions
Does mowing make grass grow more shoots?
The bermudagrass study reports that trimming stimulated the outgrowth of tiller buds and increased the number of tillers in the main stem. That is a trimming result for bermudagrass, and the study did not test a mower, so the answer for lawns in general is not settled by these sources.
Which buds respond first after trimming?
The bermudagrass study found the most significant effect at the 1st node of the stolon. It reports that trimming stimulated the outgrowth of tiller buds located at the morphologically upper 1st, 2nd, and 3rd nodes. The source reports this as a measured result.
What role does hydrogen peroxide play?
The bermudagrass study says trimming promotes a rapid H 2 O 2 burst in the leaves of new-born tillers and axillary stolon buds. Adding H 2 O 2 after trimming increased the number of tillers, so the molecule is part of the response in that study.
Can cutting too hard reduce tillers?
In the forage grass study, yes. The number of tillers significantly decreased with the increase in simulated grazing in both the jointing and flowering stages at 1 week after damage. The source also reports that the decreasing effect weakened with the prolonged recovery growth time.
Do all grasses respond the same way?
No. The forage grass study says plant compensatory growth capacity varies among plant species. The bermudagrass and forage grass studies describe two different species, so their results should not be applied to every lawn grass without checking.
How we chose
The two sources were chosen because each measures how grass responds after its top growth is removed. The first is a study of trimming in bermudagrass with measurements of sugar, cytokinin, and hydrogen peroxide. The second is a study of simulated grazing in a forage grass with counts of buds and tillers. Both are hosted on PubMed Central, and neither is a retail page.
For a closer look at the mowing side of lawn care, see why lawn grasses need proper mowing height. For a definition of the shoot this article describes, see what a grass tiller is.
