Dickinson’s poems generally fall into three distinct periods, the works in each period having certain general characters in common.
Pre-1861: In the period before 1858, the poems are most often conventional and sentimental in nature. Thomas H. Johnson, who later published The Poems of Emily Dickinson, was able to date only five of Dickinson’s poems as written before 1858. Two of these are mock valentines done in an ornate and humorous style, two others are conventional lyrics, one of which is about missing her brother Austin, and the fifth poem, which begins “I have a Bird in spring”, conveys her grief over the feared loss of friendship and was sent to her friend Sue Gilbert.[148] In 1858, Dickinson began to collect her poems in the small hand-sewn books she called fascicles.
1861–1865: This was her most creative period, and these poems represent her most vigorous and creative work. Her poetic production also increased dramatically during this period. Johnson estimated that she composed 35 poems in 1860, 86 poems in 1861, 366 in 1862, 141 in 1863, and 174 in 1864. It was during this period that Dickinson fully developed her themes concerning nature, life, and mortality.
Post-1866: Only a third of Dickinson’s poems were written in the last twenty years of her life, when her poetic production slowed considerably. During this period, she no longer collected her poems in fascicles.
Source:
Wikipedia