Extra note on the cold snap part: It appears the lows will only be for a few hours in the early mornings like 4 - 6am kind of timing.

No, it has nothing at all to do with CalTrans, musa. CalTrans has been forced to pull out dying oleanders DUE to Leaf Scorch, sadly. There are almost no living oleanders in Riverside/San Bernardino counties, most in Los Angeles are gone now, and Orange County and San Diego counties are seeing the same marching demise. Most evident along our freeway systems, since so many medians are planted with the tough oleander. Sugi, they could be, but for your purposes, you might prefer a more compact cultivar. Unless you have this kind of space and size of pots to create the same effect. Otherwise, I would consider a scaled down version. They roots are incredibly dense and deep. I would not be surprised if a full sized cultivar's roots could crack a pot. Now, does this mean you shouldn't try? I would, if I could find reasonably priced plants. But, if you start to see signs of leaf scorch, just know that the plant's days are numbered. I have a very long driveway with about 16 very large white oleander trees in total, 8 lining each side. They are spectacular. They have been in full bloom since May. It has been a very unusual year for them. They are all doing very well. Right now. But, we have evidence of leaf scorch in our yard, in our other oleanders, as well as evidence of leaf scorch in oleanders in our neighborhood. So, my husband and I know it is just a matter of time before we lose these lovely trees. Here is a pic of a couple of the trees towards the beginning of the driveway, near the house, can't find the photo I took of all the trees lining the driveway, which is quite spectacular. Patty S. Here is a link that might be useful: UC IPM: Oleander Leaf Scorch

For clay/terra cottage pots in all day sun, you are also losing a considerable amount of water through the sides of the pot. I think you have already surmised that you are both underwatering and underfertilizing your plants in our year round growing conditions. I prefer to use larger glazed pots for full sun locations to reduce water loss, and also prefer to connect containers with automatic drip irrigation. During summer in full sun, I typically water every day for 3 to 5 minutes, and if this is too much at one time,I might split it into a morning and afternoon watering. If your plants aren't growing much and show signs of moisture stress, you might try larger pots, more watering more frequently,and using both a time release fertilizer in combination with periodic liquid feeding. Or move them into less sun... pots with less water needy plants may be an option if you don't like daily watering. Succulents such as agaves, aloes,aeoniums,echeverias, etc work well. Many supposedly drought tolerant plants like California natives don't accept the same low watering frequencies of succulents, as they dry out just as quickly as normal plants with a limited root run of containers.__

Thank you so much Albert! I couldn't figure out the correct terms to search for and did not see this article. Really appreciate it!