You don't say where you are..but it cant be sunburn in December. You also left out what temps it went through. I would guess looking at that,mid 20's? or low 20's?. Right now,the real damage isn't showing..in spring you will get the full picture.
Large plants are very cold tolerant. I've seen photos of huge old plants in the southern central valley that probably saw a few temps in the teens in their time.

Do you think it'll just be cosmetic or a plant killer?

What should I see good or bad in the spring?

Btw: Austin, Tx ~ Mid 20s

This post was edited by nuxx on Tue, Dec 17, 13 at 9:13

Not necessarily a plant killer unless it starts to rot (though most likely it will unless you get no more cold). That species tolerates temps into the mid to high 20s. Mine got frost bite, too (got down to 22F).

What should I do with the plant? Should it be ok if covered better next time?

What happened to yours?

This was an extremely freak cold spell.

One other thought...

The plants were covered for 7 days straight, then the covers were taken off on a sunny (70 degree day), could it be sun burn? Almost like acclimation issues?

We were out of town, so couldn't un-cover each day.

It was the cold. They can take wide diurnal temperature swings. Its what happens in most deserts not right on the equator. But..solid mids20's for a few days in that part of Texas? Its a wonder it looks that good.
The Saguaro looks like it will be ok..the Pachy? not so good.

Thanks :)

Do you think the Pachy will die or just be discolored? The tip looks just fine... there are larger Pachy's in town that have made it through our worst winter in decades about 4 years ago, doesn't seem to be damage on them.

How can I avoid this damage turning into rot?

Seems that where an extra shirt was on top of the Pachy (tip) there is no damage. Seems to be just where the freeze cloth was by itself. Also where the wind would have hit it. Other sides / back of the plant looks fine.

I'd say lows in the 20s for maybe 3-4 hours. Then just above freezing during the day on the worst days during that streak. I don't think it stayed under freezing all day.

We were out of town though :(

BTW: Our 5' Saguaro shows no signs of damage.

This post was edited by nuxx on Tue, Dec 17, 13 at 13:20

You might try hydrogen peroxide in spring,after cutting out any active rot. Hope it heals. The scars will be forever..but if it recovers,just adds character. "My Charles Bronson cacti". Or Vin Diesel for younger folks.

Not sun damage unless you had the plant lying on its side.. .I have seen and caused sun damage on bigger columnar cacti (had a Saguaro growing in some shade for a year and moved it to a sunnier location and burned the hell out of it). But burn reflected angle of the sun. Plant recovered from burn but lost a lot of the spines along the burned ribs. Sun burn did discolor plant, but not soften it... check yours for soft spots... if so, not sure what you should do, but consider cutting the ribs off and treating them with an antifungal and try to protect this plant from any further cold for a year. Soft spots tend to spread like wildfire in a cactus, quickly rotting out the entire thing (literally eating it from the inside out... plant may even look OK until it suddenly collapses in a heap of melted goo and a crinkly outer flesh).... big mess to clean up!

Is all rot very soft?

I tried pushing on the darker areas and they still seem firm.

Next cold spell we have, I'll use the frost cloth and also use a blanket. Seemed fine where had cloth under the cloth (tips).

Do you think I'll see any changes in the look right now? Like will it spread even when it's nice outside?

lol I don't mind character. Our 5' Saguaro has a big chunk missing in the bottom that is a scar now. Just shows it's pretty old and been through stuff in it's life.

What would you guess chances of survival is for the Pachy? Also going to make sure it's a bit more protected for any under 30 temps.

BTW: Would hate to lose the little Saguaro the most. It's 18" and is two Saguaros on one root. Pretty cute, matching 18" cacti sharing the same root. Hard to find is an understatement for that one haha

Here's the sun damage I did initially, but from this it recovered... but not from being under an eave where rain dripped it too much... bummer. Had it for 6 years.

That's so weird looks so close to that...

Keeping in darkness for 7 days straight then putting in the sun couldn't do that?

Sorry to hear that :(

Checked again, looks the same, still not squishy or soft.

This post was edited by nuxx on Tue, Dec 17, 13 at 15:42