As a conductor Berglund often went beyond the printed score in the music of Jean Sibelius and others to improve on what he believed were weaknesses, especially in orchestration, colour and balance. Most orchestras he conducted responded well to his no-nonsense approach. He was tireless in studying, preparing and rehearsing. He almost always came to the orchestra with his own materials he had corrected and bowed by his own hand. He would then mark highly detailed instructions on the sheet music of each individual musician. Berglund would certainly not always agree with composers; he felt comfortable in elaborating any nuances he considered important but which the composers had not highlighted. He believed in details: "I think we have already had our fill of mushy recordings", Berglund noted in an interview by "Finnish Music Quarterly" (FMQ) in 1999. In the UK, Berglund led Sibelius Centenary Concerts with the Bournemouth Symphony Orchestra in 1965, and became their principal conductor in 1972, concluding his tenure in Bournemouth in 1979. He significantly raised its performing standards, as can be heard from the many recordings made by it for EMI during this period. He also served as principal guest conductor of the Scottish National Orchestra, from 1981-85. Berglund resigned from both the Helsinki and Bournemouth orchestras in 1979. More noticed in his native Finland was the fact that he had seemed to give up his dictatorial ways. In 1996, he was quoted as saying, "The rise in the standard of Finnish orchestras has been quite incredible...young musicians play so much better than their predecessors did." Guest engagements saw him conducting all the major North American and European orchestras, such as the Berlin Philharmonic Orchestra, the London Symphony Orchestra, the Dresden Staatskapelle, the St Petersburg and Moscow Philharmonics, the Leipzig Gewandhaus and the Israel Philharmonic Orchestras. Berglund was a member of the Russian National Orchestra's conductor collegium. He made his New York debut in 1978 with the American Symphony Orchestra at the Carnegie Hall, in a concert of Shostakovich and Sibelius. From the 1990s he became a regular guest conductor in the New York Philharmonic and the Cleveland Orchestra. Berglund made over 100 recordings. In an interview for the newspaper "Helsingin Sanomat" in 2009, he said when asked about his recordings, that the Smetana recording with the Dresden Staatskapelle is probably the best, since this was the best of the orchestras that he made recordings with.