Flight

[Erthona]

It is the lie of birds - that you need wings, (for me the hyphen gets in the way, I don't think you need it)
the lie of time that gravity
brings you to the ground, presses ("wings" "brings" is a nice internal rhyme. Shouldn't presses be pressing?)
like a pillow against your face;
soft, unbreakable. (Rhythmically I could go with an "and" between "soft, unbreakable")

The clouds of summer call (As you are personifying clouds, I think you could drop the direct article for greater emphasis)
like cold salt-cream, but wait - (Again, I don't think the hyphen is doing what you think it is. Another nice internal rhyme with "wait" and "striated")
till autumn forms
as long striated runways in the sky, (It's possible that a more organic approach would work better here, something like "wrinkled".)
then climb (breaking this here only made me have to go back and read it again, I don't get the point)

higher than the the jealous, root-bound (earth-bound, they cannot be root bound in the sense you are meaning it, root-bound is a term used when plants are basically suffocating themselves because they have not been re-potted into a large pot)
trees can stretch their branches,
hooked and bare like knuckled grasps.
Go to where the cliffs tower,
where the sea crashes far below and mists (grasps-crashes, again nice internal rhyme)
up in a howl of billows, the pale blue (I'm all for terseness, but "mist up" needs more support. Maybe "and the mist billows up"?)
of a loose night shirt. (whatever you are trying to image here, it passes me by)

Link arms and dive (I'm not sure how one "dives upward" plus I have no idea whose arms are being linked )
upwards till the sound of surf,
breaking bones on rocks, (whose bones?)
dissolves in white-noise static.
Twist through the clouds (beginning this sentence with a dependent clause seems problematic, maybe "we/they twist"?)
in their spectre-gray grave linens ( maybe drop the "gray" and go with spectral, or maybe "ghost-gray grave" for some extra alliteration. I don't know, it just reads odd to me)
to where the oxygen is rare (although factual, the phrase is a bit overused. What it literally means is where there is little air and so one would pass out. It only makes sense in its idiomatic form, which means to "clear my thoughts", or "the elite". which is a bit cliche)
spun candy on your tongue, (I have no idea what this refers to, but I like the image)
cast off earth-heavy thoughts,
close your eyes
and fly.

Overall, this has some nice images, but maybe lacking some in substance:

Birds lie. Say we need wings. But we can fly in our imagination. Use it to fly into bliss/joy.
Sky=joy/happiness/serenity. The earth=negative/depressive thoughts.

Overall the main problem for me was the introduction of subject on which no background was given e.g.:

"of surf, breaking bones on rocks,"

Whose bones? Were the people whom the speaker was addressing? Had they let their body fall when climbing into the sky, or are they metaphorical bones, where bones=heavy depressive thoughts. The first makes little sense unless you are advocating suicide, and one has to guess a lot to come up with bones as metaphor, at least that's my take.

Dale