Jamieson, Fausset and Brown on Hosea 14:5

5. as the dew--which falls copiously in the East, taking the place of the more frequent rains in other regions. God will not be "as the early dew that goeth away," but constant (Ho 6:3, 4; Job 29:19; Pr 19:12).

the lily--No plant is more productive than the lily, one root often producing fifty bulbs [Pliny, Natural History, 21.5]. The common lily is white, consisting of six leaves opening like bells. The royal lily grows to the height of three or four feet; Mt 6:29 alludes to the beauty of its flowers.

roots as Lebanon--that is, as the trees of Lebanon (especially the cedars), which cast down their roots as deeply as is their height upwards; so that they are immovable [Jerome], (Is 10:34). Spiritual growth consists most in the growth of the root which is out of sight.