The rose used to be the preferred flower in the gardens of england and symbolised the House of Lancaster and York both influential on the crown. The rose was therefore adopted as a symbol of england

As above, but additionally the red rose is the symbol of Lancashire, and the white rose that of Yorkshire.
The heraldic rose on the royal coat of arms is a combination of the two.

The national flower of England is the rose. The flower has been adopted as England’s emblem since the time of the Wars of the Roses - civil wars (1455-1485) between the royal house of Lancaster (whose emblem was a red rose) and the royal house of York (whose emblem was a white rose).

The rose was also the symbol of the Tudors, of which included Henry VIII, until the Stuarts took over.

So i guess the rose was kind of the favourite flower - also if Henry VIII, adopted it for a few years, who would disagree with him eh!