I've been growing an Acacia Acuminata since November. They're nice trees and I figure that they'd go well with some of the other funky plants me and the SO have been growing.

Now, the weather has warmed up a lot here and the sun has been out a lot. Foolishly, I put the Acacia out in the direct sun for too long and burned it pretty bad.

The plant only spent a few hours in direct sun, but all the little baby leaves have fallen off. The "stems", which appear to also be leaves, are still green. Attached is a picture of the plant after a week of recovery.

Any insight into the health of my little tree would be deeply appreciated. Will it survive? What can I do to help it recover?

As you found out, that seedling is way to immature to be thrown into full on sun like that. It's shocked. Acacia acuminata does just fine in bright shade here in the PNW, right through summer and winter. I don't bring it indoors and I don't baby it at all. It's been through frosts, light snowfall and the mild rainy winters common here in temperate rainforest and is a few years old now. I am not sure what climate zone you are in, but I would just leave it in bright shade and let it recover and grow.

This is my acuminata I just leave outside. It's not even sheltered through the winter here from the rains at all. Its been through nights at -7C and didn't even look stressed.

jamie:

I live in Zone 5b. We're due for some snow this week (for a few days straight), so I'll put the plant in my south-facing window (if I can find any room, our house is about to burst from all the plants)!

I may try growing a second tree such that when it sprouts it will be past the last frost date here (early May is usually the safest bet here).

So for now I will let the plant recover.

If I might ask a follow-up question: how much water would a plant of this size need daily? I'm not sure how to convert the mean annual rainfall (225-500 mm) to mL of water per day or every n days.

I cant really comment on water requirements for acacias. I just water mine whenever the soil is dry enough so that I cant squeeze any water out of it. But then, I also leave it out through the winter rains...

I live in a temperate rainforest. It rains a lot.

Acuminata should be frost tolerant (at least the burkittii subsp should be) the middle semi-arid/grasslands/deserts of Western Australia readily reach sub zero at night. Daytime temp is probably a more important variable to consider than light.
If you look at Jamie's acuminata, you will notice the shape of the shrub. It's mechanics are quite distinct and perfectly suited to either withstand strong winds or the opportunistic jaw of a hungry camel.
The climate of these regions is subject to the chaos of the southern ocean as it hits the dry, heat of middle Australia. Lots of electrical activity and storms and such.
I would keep your watering pattern as chaotic as possible once the little guys have established themselves
And by the looks of your little baby with its new phyllode growth I'd say it's ready for a sandy/loam pot up (if not already in a sandy/loam medium)
The pinnae (tiny leaves) falling off coupled with the phyllode growth are a good indication of a healthy plant, if you can keep daytime temp above 5-10deg C that would definitely help the growth.

That's encouraging! So far I've been watering it only a few times a week (once the top layer looks totally dry for a day). It has already been transferred to a large pot with an approximation of western Australian duplex soil.

The top layer is a mix of cactus soil (porous volcanic rock chunks and some soil), sand and some diatomaceous earth (maybe vermiculute would have been better). The lower layer is loamy potting soil with some compost, diatomaceous earth and sand in it to keep it fluffy and nice.

Since it's still green I guess I have reason to be optimistic for when the weather begins to warm up.

Since the plant has been growing indoors and quickly went into shock from the direct sun, I was wondering if I should keep it in a greenhouse to diffuse the sunlight, or if that would be too bright/humid for it.

Thanks for the responses!

G'house would be fine for a couple of weeks until it acclimatises to the light, just keep the flap open if it has one good luck!