Grass pollen, the most clinically relevant outdoor aeroallergen in Europe and worldwide, presents a complex challenge due to the diverse nature of its subspecies. This diversity complicates the interpretation of their contribution to the overall pollen burden during the grass pollen season and the selection of the appropriate allergen immunotherapy. Almost all species of the Pooideae subfamily share important major allergens, namely the allergens of Group 1 and 5, leading to a high level of cross‐reactivity at the IgE level. However, the presence of a multitude of additional minor allergens and species‐specific epitopes adds to the complexity. Timothy ( Phleum pratense ), previously considered the most relevant allergen source among grass species, is found during the late‐blooming grass pollen season, while symptom severity and pollen concentrations already show several peaks during the early‐blooming grass and main grass pollen seasons. Current data suggest a limited regional relevance of timothy grass during the natural grass pollen season in southern Europe from both the aerobiology and allergy perspectives. This review aims to discuss the latest evidence supporting a broad‐spectrum approach to best reflect natural grass pollen exposure in allergen immunotherapy, presenting a complex but crucial aspect of allergology.