Hello,
We had for New Braunfels a relatively cold night with tens in high 40s this past week. I think the brown in the leaves is fit to that drop in temperature. Does that look like the case? Should I prune the damaged leaves?

If the outside leaves are damaged but the inside leaves are good, yes, cold damage. As new leaves grow, they should look healthy. It doesn't matter if you remove or leave the affected leaves - its cosmetic.

N.B. Howdy
If low temps still like that. Get some cloths-pins, and hang some rags over them at nite. OR ! You could hang some thin, semi-transparent rags over them, and just leave them hanging, till weather warms up.
Actually, hot-caps would be best 👍👍

😎😎😎

I'm in waco, tx. I got a pretty late start on planting my garden this year so all of my plants are still pretty small. We have been having 70-80° days and 40° nights and now it seems that all of my plants have discolored brown and/ or yellow leaves. I'm hoping it's just from the temperatures and not something else going on. This is the first time I've had this problem.

Plants do not like massive temp changes especially when they are young.
They go into what I call shock. They may not die but will often just sit there doing nothing for an uncomfortable amount of time.
The fact yours have brown like that is not good, so you had best cover them at night.
When I have planted early spring , taking a gamble up here, often when we get twenty plus degrees temp. swings, day to night, I have had them sit for a month doing nothing, even when temps. rise but when I have seen brown like that, often they simply die, slowly.

One of he best ways to deal with cold like that , besides covering them is to water them heavily before sun down.
It is one of the ways we combat frost in the fall as the evaporating rising water keeps the plant warmer.

RpR said:Plants do not like massive temp changes especially when they are young.
They go into what I call shock. They may not die but will often just sit there doing nothing for an uncomfortable amount of time.
The fact yours have brown like that is not good, so you had best cover them at night.
When I have planted early spring , taking a gamble up here, often when we get twenty plus degrees temp. swings, day to night, I have had them sit for a month doing nothing, even when temps. rise but when I have seen brown like that, often they simply die, slowly.

One of he best ways to deal with cold like that , besides covering them is to water them heavily before sun down.
It is one of the ways we combat frost in the fall as the evaporating rising water keeps the plant warmer.

So are my plants pretty much done for? Should I plant new ones? The weather has been weird this year. I was so worried about how late I planted the garden this year. I was nearly a month late for the normal planting time here but now I'm wondering if I should have waited even longer with this crazy weather.

Water and cover at night, you will see changes that will tell what they are doing.

Thanks everyone for the replies. Forecast looks like the cold is over for us.

Britty : Welcome.
Do as RpR suggests.
Spring, if you want to call it that ?
Spring hear, has been crazy also.

When weather warms, I would plant some more seeds.
Call it : Insurance. 👍👍

Ta. Ta.
😎😎😎