Fetching details from the dictionary...
to begin to open; to come out
to smile broadly
to come apart at the seams (clothes)
早春に梅の花が綻んだ。
The plum blossoms began to open in early spring.
春の陽気に桜のつぼみが綻んでいる。
The cherry blossom buds are beginning to open in the spring warmth.
固く閉じていたバラが少しずつ綻ぶ。
The tightly closed rose is gradually opening up.