<p>Teff (<i>Eragrostis tef</i>) is a high tillering cereal with small grains, limiting its yield and harvestability. Conventional breeding has prioritized high tillering, but excessive tillering can negatively impact grain size, increase lodging risk, and result in uneven grain maturation. This study evaluated the effects of exogenous application of a synthetic strigolactone analogue and 1-naphthaleneacetic acid on tillering and assessed their effects on grain size and yield components in teff. In both experiments, foliar application of strigolactone and 1-naphthaleneacetic acid significantly reduced mature tiller numbers by 20–35% through suppression of tiller emergence. In the second experiment, earlier application and increased frequency further reduced both mature and total tiller numbers. Moderately reduced tillering by the treatment of strigolactone and 1-naphthaleneacetic acid increased grain size by 12% and 8%, thousand-grain weight by 20% and 14%, and yield per panicle by 36% and 25%, respectively. Excessive tiller removal, such as through manual de-tillering, reduced whole-plant yield due to a decline in panicle number. Moderate tiller suppression led to improvements in whole-plant grain yield and harvest index. Grain size, thousand-grain weight, and yield per panicle were negatively correlated with tiller number, suggesting enhanced resource allocation to the primary/more productive tillers. While PGRs showed promising short-term effects, compensatory late tillering after treatment ceased limits their field application. These findings indicate that reducing excessive tillering, especially late-emerging tillers, can enhance grain size and yield traits in teff. Genetic or breeding approaches that modulate strigolactone and auxin signalling pathways may provide a sustainable strategy to enhance grain size and yield in teff.</p>