There is sweet music here that softer falls Than petals from blown roses on the grass,
These lines open up a new stanza, and a whole new section of the poem. This stanza is the first part of what Tennyson calls the "Choric Song." That basically just means that all the sailors who ate the Lotos have gotten together in a chorus and are singing about why they don't want to go home.
In this new section, the speaker of the poem has shifted from the narrator we met in the first five stanzas. Now there are many speakers (all the sailors who ate the Lotos plant) speaking at the same time.
They start out by telling us what seems so great about this new place. For starters, they say, there is "sweet music" in the land of the Lotos-eaters. In order to describe it, they use an analogy, saying that this music is "softer" than a petal falling from a fully bloomed ("blown") rose. So it's really, really, soft, basically—like clouds of cottony bunny tails soft.
Or night-dews on still waters between walls Of shadowy granite, in a gleaming pass;
The singing sailors use another little metaphor here, comparing the softness of the music in their new home to the softness of the dew that falls on water in a high mountain pass.
Tennyson weaves in nice little echoes throughout "The Lotos-eaters," repeating images in different parts of the poem. Here the "night dews" might remind you of the evening dew that fell on the three mountains in the second stanza (17).
Music that gentlier on the spirit lies, Than tir'd eyelids upon tir'd eyes;
These sailors really want you to know how soft and gentle this music they hear is. It's even gentler, apparently, that "tir'd eyelids upon tir'd eyes." Be sure to notice that repetition of "tir'd" (that's just an old fashioned spelling of "tired" by the way).
Like he does in a other places (see lines 41-42), Tennyson uses this repetition to emphasize the importance of sleep imagery in this poem. It's almost like the sailors are trying to hypnotize us. Sleepy… you're getting sleepy…
Music that brings sweet sleep down from the blissful skies.
Just to review: the Lotos plant makes you sleepy. Everybody got it? You probably figured that out by now, right? Still, Tennyson wants to make sure you're extra focused on that idea.
The music these sailors hear is like a lullaby, and it makes them happy. It makes them look forward to "sweet sleep" (alliteration alert!). Even the skies seem "blissful" in this musical spot. Or maybe that's just the Lotos talking…
Here are cool mosses deep, And thro' the moss the ivies creep,
We get just a little more natural detail here. The sailors give us a soothing image of "cool mosses deep"—just the kind of place where you'd want to take a nap. Yawn…
We're not sure exactly why we need to know about the ivy that creeps through the moss, but it sure sounds pretty. This is probably a good place to point out that, even though we're in a new section of the poem, the rhythm is pretty much the same—still mostly iambic. Line 54, in fact, is perfect iambic tetrameter—four pairs of syllables with the second syllable stressed: And thro' the moss the ivies creep. Try saying it out loud—hear how even and calming it is? We think it's just another way for Tennyson to emphasize the soothing, soporific (sleep-inducing) mood of the poem.
And in the stream the long-leaved flowers weep, And from the craggy ledge the poppy hangs in sleep."
Here's a little more info on the plants. In this case, both the "flowers" and "the poppy" are personified. The flowers droop into the water of the stream as if they were weeping (kind of like when we talk about a "weeping willow"). The poppy hangs off the edge of the cliff as if it were asleep.
(Fun fact—the association of the poppy with sleep is an allusion to the fact that opium is extracted from poppies. Opium has been used for centuries to ease pain and bring on sleep. Heck, the connection between poppies and sleep even shows up in the Wizard of Oz.)