I have two small jade plants (see pictures). The leaves of the larger one are turning brown, and now the leaves of the smaller one are too. I don't know if they're burning from too much sun (I've had them in full sun, but we're consistently in the 90's - although we had a week over 100 - yuk!) so I moved them to a shady location. Or maybe I'm overwatering or underwatering them (~1-2 times a week when it's this hot). Or perhaps it's a pest or disease? All ideas are welcome.

I think it's most likely too much sun. The brown spots look like sunburn to me. So, well done, you've taken care of the problem already. Be sure to water it less now that it's in the shade.

Jade plants are grown by many people indoors where there's never full, blazing sunlight and they do very well. So I would think outdoors, a nice shady spot would be the perfect place for them for the summer. Most plants commonly grown as house plants need at least bright shade (such as under a thin tree) when they're outside for summer vacation.

Jade plants can handle full sun no problem in mild climates. I prefer the way they grow in full sun... much more compact, solid, stable.

I imagine two ways the sun could harm your plant, and conceivably lead to the leaf signs you are seeing. First there is the danger of moving a plant from low light (say indoors or in deep shade) right into lots of midday sun this time of year. With jades and other succulents, gradual stepwise changes are always a better way to go, so as to give plants a chance to develop some resistance over time. Second there is the danger of too much sun when it's oppressively hot (esp. when temps don't cool down at night)... depending on the climate, full sun can be too much for jade plants at the peak of summer. The danger there lies in the one-two combination of intense overhead rays and heat stress. We don't experience that kind of heat here so I give my jades as much light as I can.

Paradise is just plain hot! (I'm from Oakdale) And it looks like your plants are sitting in the sun and you are overhead watering. That will burn them every time. If you have to get the leaves wet to water, do it in the early evening. Don't worry about wet leaves at night - it doesn't cool down enough for problems to develop.

That was my thought too. It looks like the burned spots are where water pooled on the leaves, magnifying the sun.

That is indeed too much sun damage. Try to find a more part shade area. I grow mine outdoors, but I have the canopy of trees that provides dappled shade to my jades during the hottest part of the afternoon and have endured nicely our triple digit heat and beyond. I typically do a once a week thorough watering for them when our forecast calls for extreme dry heat.

If these jade plants of yours are still relatively new, all the more you have to acclimate them slowly to outdoor conditions. In my area they are more actively growing during the cooler months, but they do take up water eagerly during the super hot days, so you can see good thickening of the trunk. Also try to water directly the media, do not spritz on the leaves, their stomates are closed during daytime, and it will lessen chances of fungal attack.

At times too, the succulents tries its own coping mechanism, it will drop the lower, older leaves, and will just sustain the ones nearest the tip, the rosettes will be a tighter growth. It is trying to conserve its resources, so do not be tempted to overwater when you see that.

The color of your jades stem, is still green, so it is still very young, I find that once they start forming that harder, bark cover on their trunk, then they are better able to cope with the extremes of the weather. So best to position in a good light area but in part shade for now.

That's true. Mine always were in the shade by about 4pm.

Sunburn. Even though my plants are adjusted to being in the sun all day by the time summer is over, going into house or greenhouse for winter negates that. When these plants go back outside, there can be some sunburn. A gradual re-adjustment is necessary to avoid sunburn, sometimes easier to know and say, than do, especially if the trees do not have leaves yet and the shadows are not where they usually are.

Water had nothing to do with the burns I photographed here:

Thanks, everybody.! I was pretty sure it was sunburn, but it wasn't until I read Daisy's post that I realized the exact cause. I water in the morning before there's direct sun on any of my plants, and I do try my best to water the media, not the leaves of plants. It didn't occur to me that because of the leaves' shape the water would linger on the jade, setting up the perfect situation for sunburn. Both plants are in mostly-shade right now; I'll re-introduce them slowly to bright light and pay closer attention when I water.