Stanza 3 Summary

Get out the microscope, because we’re going through this poem line-by-line.

it grows back, a stump of a shoot
grows longer, grows moist, grows strong veins,

Something's growing back here, gang. That's great—now what was our speaking talking about again?
Oh right, here we're picking up from the first stanza, which left off with the speaker talking about what goes on while she dreams.
Line 31 picks right back up after an extended enjambment to let us know that "it" grows back. Remember that, when we last left our reader in English, she thought that she had spit out her rotten mother tongue.
Here, though, while she dreams, the tongue starts to grow back. You can't keep a mother tongue down, it seems.
Remember that this idea of a tongue representing an entire language is a fancy metaphor called metonymy. And don't look now, but there's another metaphor headed our way in these lines.
This one compares the speaker's tongue to a plant that grows back after being cut down. This might sound a bit weird, but plants and tongues have a few things in common: they're both moist and they both have veins, after a fashion.
It looks like our speaker's mother tongue is growing back stronger that ever.

it ties the other tongue in knots,
the bud opens, the bud opens in my mouth,
it pushes the other tongue aside.

Now, we're not sure how much gardening you do in your spare time, Shmoopers. If you're like us, your green thumb consists of forgetting to water the mini cactus on top of your fridge.
Still, we all know that some plants—like vines—can choke out other plants when space is limited. That's a bit like what's going on here, as the language = tongue = plant metaphor continues.
Now, we learn that the speaker's mother tongue ties the foreign "other" tongue in knots. To have your tongue tied in knots is yet another metaphor for not being able to speak. So here the mother tongue has the power to silence the foreign tongue.
It also has the power to grow buds, as the speaker sticks with her tongue-as-plant metaphor. Remember from your Life Science class that the bud is the part on a plant that turns into a flower. The speaker uses the flowering metaphor to describe the way in which her mother tongue expands and flourishes in her mouth, crowding out and choking off the foreign tongue.
If all this language-tongue-plant talk has you confused, don't fret. It's important also to keep in mind that all of this is going on while the speaker is dreaming, so that might help to explain some of the weirdness here.
To sum it up for all you non-gardeners: while our speaker dreams, her first and native language comes alive inside her, pushing aside the foreign language that she can't ever really know—good times.

Everytime I think I've forgotten,
I think I've lost the mother tongue,
it blossoms out of my mouth.

These lines end the poem on an upbeat note. Sure, it may be difficult to have to make your way through the world without your native language, but it never really leaves you.
Take our speaker, for example. Every time she thinks she's forgotten it for good, her mother tongue "blossoms out of [her] mouth" (38).
But how can you talk with a mouth full of flowers? That's not the point here, gang. This last image is one that captures the joy and peace of being able to speak in your first language. Capisce?