Well, it can't be cold damage, so my guess is too much water. (I don't have that cultivar, but my cordyline only get watered 3x weekly.) Or, perhaps it's in a location that only recently the sun has shifted its arc so the leaves get sunburned? (This seems unlikely...) Pretty garden shot, that first photo.

Wish I knew. I killed mine.

Oh boy, I was thinking of cutting back watering to my planters to every other day. But now the temperatures are going to slowly climb back to 100. It's been 85, 88, 92, and expected to go higher tomorrow.

Hopefully someone can help me! I love this plant, it stands out so nicely in my garden!

It looks like it might have gotten burnt foliage from a heat wave, from what I can see in the photos. The newest foliage that is more vertical seems entirely unaffected, and the flatter leaves at the tips seem to be the ones that got crispy. I'd suggest mulching around the base of the plant to retain moisture, trim off the burnt parts to better track if this is getting worse or was a one time event, and when you water, it is probably better to water for at least 5 to 10 minutes with spray irrigation and not do this every day unless necessary to get new plants established. Cordyline australis cultivars should actually be pretty drought tolerant and get by with just once a week deep soaks even in 100 degree weather, if the soil is well mulched.

On the other hand, this is a species that comes from New Zealand where it seldom gets to be 100F for weeks at a time, so it could just be the heat. If this continues to happen every summer, even as the plant becomes deeper rooted, this would seem to indicate that in your climate with your summer heat, it would prefer some dappled shade at the hottest time of the day, rather than full sun. The green leafed Cordyline australis species is certainly much hardier/resistant to sunburning, the newer colored forms are more prone to sun damage with high heat.

Mine did the same thing-- I have one in a pot in full sun-watering when needed. I think it is sunburned because some of my potted succulents also seemed partly burned on the parts where the hottest rays hit it-- that was some heat wave! Glad it's over.