The data used in this pollen calendar is based on research of the NPRU. The tree pollens included in this data are the hazel , yew ( Taxus ), elm , alder , willow , ash , poplar , birch , plane , oak and pine , while the main weed pollens included in the data above are oil seed rape ( B. napus ), dock ( Rumex ), nettle , lime ( Tilia ), plantain and mugwort .

The above calendar provides an indication of the period within which pollination for these trees and weeds can be expected to take place. However, it should be noted that pollination periods for each tree and weed differ greatly. More precise data (e.g. peak pollination periods for specific trees and weeds, etc.) can be obtained by referring to the data source for this pollen calendar. The grass data is based on the true grass family ( Gramineae ). As a person who is allergic to one type of grass is usually allergic to most others, the above grass data is generalised.

[1] National Pollen Research Unit, University College Worcester, UK: http://pollenuk.worc.ac.uk