。
The tree is putting out buds.
Literal
Tree [subject-が] buds [object-を] is-blowing-out.
芽を吹く ('to put out buds,' literally 'blow buds') is a poetic collocation for budding, using 吹く ('to blow') in a metaphorical sense — as if the tree is exhaling its new growth. Sits alongside the more neutral 芽を出す ('put out buds') and the spontaneous 芽が出る ('buds come out') — three verbs for the same phenomenon, each with a slightly different flavour.