Welcome, Socaldawg!
How far from the coast are you? Red Cordylines can only take a certain amount of heat and low humidity. They can grow in full sun in Sunset zones 24 and 23. In zones 22, 21, 20, and 19, they need part to full shade when the heat starts to build--like now. In zones 18, 14, and 13, they have a tendencyto die in the summer no matter what their sun exposure. We are in Sunset zone 13, and ours--in the shade--are starting to show distress now.

Thanks for responding! I'm in Anaheim Hills about 15 miles from the coast. We don't get a lot of humidity, but it does get warm (100's during the summer). I was under the impression that they could withstand full sun...? Apparently not. So, are they dying / dead? Again, it appears as though they have new growth.

I grow Cordylines here in hot tropical Australia in various spots ... full sun to part shade. I've found that the ones that get brownish/greyish spots on their leaves are in fact not getting enough water ... it's usually water stress.

Water stress would also affect the new growth.

Despite growing some of mine in an irrigated section of the garden, the water wasn't getting down to the root ball. It was only reaching a few centimetres underneath. The soil was not holding the water ... have you checked to see whether this is happening where your Cordys are growing?

If this is the problem, I can suggest a solution that worked for me. I treated the plant and the soil around it with a spray-on wetting agent ... you can also use the granular stuff ... and then watered every day for a couple of weeks.

We have a conditioning agent here called Seasol which helps the roots to grow ... I use that on my Cordys all the time. Don't fertilise your Cordys until you have solved the problem though, as fertilising sick Cordylines often makes them worse.

Thanks, but how would I check that? Also, how would Agapanthos do in this kind of heat / full sun?

Anaheim hills should be close enough to the coast for growing in full sun. If it's a drip system, 10 minutes every other day may not be enough water, depending on the rate of the emitter, even though I would say that it is way too often, especially if they are more than a few months old. Better to water established plants more at a time, and less often. I would also check for spider mites.

No, it's not a drip system. How do I check for spider mites? As you can see, I'm really new to this gardening-thing. I'm finally getting my lawn up-to-snuff and have turned my attention to the "gardening".
Also, how would Agapathos do in my zone? I'll try and add some pics soon.

Thanks again.

We don't have any heat problems but when I planted some apple trees years ago I was still working and drip systems were unheard of for amateur gardeners. My GC owner told me to plant with a piece of 2-3" drain pipe going from the surface down to the bottom of the root and about 2' above the ground. I had to fill that daily until they were established. Could you use a probe to make a hole and insert a pipe down to the root?

Hmmm...that sounds interesting. I've never heard of doing something like that. Anyone else heard of doing that? How do I check for spider mites?
I've seen other Cordys around my area that are doing just fine. I'm not sure what I'm doing wrong.

Ugh! Frustrating.

To check for spider mites, hold a piece of white paper under the leaves, and give the leaves a sharp rap or two. If there are spider mites, you will then see tiny (12 point period sized, or smaller) green, tan, or rust specks running around on the paper.

The pipe method of watering can work, but often backfires here in the American West, because so many of our water supplies have a high sodium content. If you are working off of well water, Socal, it might be okay, but Colorado River water is bad news. Watering from the bottom up concentrates the sodium near the surface, where most of the feeder roots are.

If watering from a hose, the best way is to have a basin as wide as the plant, and an inch or two deep. Put a bubbler on the end of the hose, drop it into the basin, run it fast to fill the basin, then run it sslloowwllyy, to just keep the basin full, for about 2 hours. That should be done about once a month on well established plants, or maybe once every two weeks when the Santa Ana winds blow. That pushes the salt down below the roots, and encourages deep rooting. Relatively new plants will need less water, more often.

I saw the pictures, Socaldawg! Several things are a possibility. My first suspect would be salt damage, from too shallow, too frequent waterings. The next possibility is magnesium deficiency. The third is spider mites, as above. The fourth is a mild frost damage, but that is fairly unlikely in your location--I would rule it out, if it weren't for the monster winter we just had here in Arizona!