A little help please

Today I've got a couple of plants that might be in trouble. As they're new for me this year I'm unsure what is going on, and am asking for some help.

The first is an Agave. In the spring I bought five or so Agaves from Cistus nursery, potted them all up in clay pots, and let them grow. The one above is an example of a healthy one -- there's nothing wrong with it (other than the spurge growing there).

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Here's the sickly one though:

I'm not sure if it comes across in the photos, but it has a bit of a yellowish cast, and it's certainly not full and healthy looking like the other Agaves that were put in the same potting mix and kept side-by-side all summer.

Here's another good one:

And here's the bad one again:

Here are a few of them in the same image for comparison, with the sick one at upper left:

So, can anybody tell me what's wrong with this one?


Another plant I'm growing for the first time this year is Cylindropuntia leptocaulis, or Christmas cholla. These plants have been growing great all summer, but have recently turned brown on the oldest growth:

When this showed up on the first plant (I have four of these), I thought it was rot. When the rest of the plant looked fine a month later, and when the three other plants started doing the same thing, I started thinking this was normal.

So, is this something to be concerned about, or is it normal for this cholla?

Help!


(If you know the answers to both of these questions but only have time to answer one, please answer the Agave question.)

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