Sibelius's last solo song collections (opuses 86, 88 and 90) were completed during the years of the First World War. These collections represent the final period of Sibelius's development as a writer of solo songs: classically reserved expression and simple formal structures replace dramatic recitation and Late Romantic or expressionistic stylistic tendencies. Moreover, there is less concern with directly reflecting the atmosphere of the poems through the structures of the pieces and the piano writing. Now we have a kind of "Neoclassicism" - but the starting point is not the Viennese classical school as with later Neoclassicists (or the Baroque as with Igor Stravinsky). Instead, these songs are based more on the Romantic model of the composer's early output, and especially the model as it was adopted in the Nordic countries. Nevertheless, the musical language and expression are more reserved than in the composer's early career. In these late songs Sibelius seems to strive less for songs on a grand scale - as was often the case in his earlier collections. Now he creates miniatures. Moreover, the piano is used differently: we no longer hear so many chords and long tremolos, and the entire texture has become more traditional.
In all of the last songs the song parts tend to be lyrical. This is presumably due to the fact that Sibelius wrote all the last opuses for Ida Ekman, who had "apparently asked for new pieces for her repertoire" (a point made by Erik Tawaststjerna). Ekman gave the first public performance of the first five songs of opus 86 in October 1916, at a series of four concerts presenting Sibelius as a composer of songs.
Opus 86 was written a little before the second version of the fifth symphony, in the autumn of 1916. The first piece of the collection Vårförnimmelser (words by Tavaststjerna) is a small-scale, joyful representation of spring; the change of key from D major to F major in the middle section of the song enlivens the otherwise stanza-bound structure of the song. Längtan heter min arvedel (no. 2; words by Erik Axel Karlfeldt) and Och finns det en tanke (no. 4; words by Tavaststjerna) are the philosophical songs of the collection. The piano parts in both these songs have been utterly scaled down - in the latter case one could speak of a kind of minimalism. In Dold förening, too (no. 3; words by Carl Snoilsky), the piano rhythms remain completely unchanged throughout the song. Sångarlön (no. 5; words by Snoilsky) requires long legato lines. Erik Tawaststjerna has compared it to Var det en Dröm, but this is not entirely fair: the later song does not seem to aim at the romantic glow which is evident in the earlier one. The collection ends with song no. 6, based on Mikael Lybeck's poem I systrar, I bröder, I älskande par! The nimble chromatic accompaniment has parallels with a later song, Små flickorna (1920).
At the beginning of the summer of 1917 Sibelius started to choose poems for a new song collection which he was writing for Ida Ekman. As his motif he chose flowers, which were also the theme of his piano opus no. 85, composed at the same time. The collection turned out to be a selection of poems on a flower motif by two Romantic poets, Frans Mikael Franzén and J. L. Runeberg (three poems by each poet). The settings were completed on 16th June 1917. Sibelius called this collection a song cycle, unlike his previous collections. Ida Ekman, who was coming to the end of her career, performed the songs for the first time at her jubilee concerts in October 1917.
The flower cycle continues the crystallisation of forms and the miniaturism that had begun with opus 86. As Kim Borg has pointed out, "The cycle's fascination lies in its modesty and quiet reflectiveness. It has something in it of the 'ancient Golden Age', of the real 19th century." The pieces are tinged with a delicate melancholy and with Slavism; the musical parallel of the fragile beauty of the flowers lies in the simplicity and sensibility of the settings. The poems can be seen to form a life-cycle moving from spring to autumn. Blåsippan (no. 1; words by Franzén) is the only jolly song of the cycle; we hear the warbling of a skylark in the piano part. De bägge rosorna (no. 2; words by Franzén) anticipates the last song in the cycle both in the themes of its Slavonic melody and in its waltz rhythms. Vitsippan (no. 3; words by Franzén) shows how, in music as plain as this, great significance can be achieved by small changes in the piano texture. As in some early Runeberg songs, the melody of the fourth piece in the cycle, Sippan, resembles a Finnish folk melody; Erik Tawaststjerna has described it as a Karelian folk song. Törnet (no. 5) is the most grandiose of the compositions. In the manner of the earliest Runeberg songs it tends to grow from brevity to monumentalism. The melodic line is related to the song Se'n har jag ej frågat mera. The last song of the cycle, Blommans öde (no. 6; words by Runeberg) tells of the fate of a flower in autumn. As the song progresses, the melancholy Slavonic composition turns out to be a waltz.
For his song collection opus 90 Sibelius used only texts by Runeberg. The collection was created soon after the previous collection, in December 1917-January 1918, just before the Civil War broke out. These six songs continue in the style of the previous collections, but the composer no longer strives for quite the same brevity and conciseness. In several songs the composer approaches the models for his early songs. For example, Morgonen (no. 3) is actually a late "little sister" of Fågellek, composed thirty years earlier. Overall, there are similarities in the keys, the piano parts, the formal structure and the atmosphere of the songs. Fågelfängaren (no. 4) is a recollection of the merry fowler in The Magic Flute, presented in the spirit of Schubert - the figure is related to the young hunter in Jägargossen. The devout Vem styrde hit din väg (no. 6) is related to the song Hundra vägar. However, the echoes of earlier songs do not seem to represent a regression, since these late songs, too, are dominated by classical restraint and intimacy, rather than by the romanticism of the early songs. The climax of the collection, representing also the most "modern" facet of Sibelius, can be found in the first two songs, Norden and Hennes budskap. In the first song, Sibelius seems to gives wing to the swans' longing for the North through the use of a continuous crescendo lasting through the entire song, and by means of a flexible legato in the piano part. Song no. 2 portrays a message sent with the north wind by a sad girl who is longing for her lover. The setting is notable for the intensity of its phrases, separated by pauses. According to Erkki Salmenhaara, "the song combines the tonal tension between F sharp minor and C major in a psychologically dramatic way." Opus 90 was to be the composer's last full song collection. It may be that the sense of longing and the nostalgic tone of the songs in the collection foreshadowed the end of Sibelius's song production.