RE: Cordyline

Paolo Mottola wrote:

>I have a Cordyline australis that shows the symptoms you
>can see in the attached image.
>The leaves  start showing those yellow areas from the
>base of stem (new leaves on top seem healthy).
>The other stems of the plant look healthy too.
>This Cordyline grow in a rather compact soil.
>
>Any idea?

I had a good look at the photo Paolo and my immediate reaction was that all 
of my Cordyline australis looked the same on the older leaves, so I had a 
good look round the garden today to check. I counted 25 Cordylines 
altogether and every one has some yellowing. Jerry Heverly has just pointed 
out that they are susceptible to fungus that results in yellow splotches 
over the leaves. I always wondered what caused that, (thanks Jerry) as the 
majority of mine have yellow splotches over their older leaves. A couple of 
my trees have more extensive yellowing on old leaves than shown in your 
photo, but many only show yellowing at the tips.

It has always been my impression that Cordyline leaves do go yellow before 
they die, and the older leaves die as the plant grows, hang down in a skirt 
all down the trunk and then finally drop off after a few years. The few 
photos I have found in books are of such majestic specimens that you don't 
get a good close-up look at the leaves to see if they are showing yellow 
patches on the older leaves. My specimens are in various soil conditions, 
some in very waterlogged clay soil with bad drainage and little topsoil, 
and others that are very well drained. Some are in very poor compact stony 
soil (edge of a driveway) and others in good loam. As a sweeping 
generalisation I would say that those that are better drained have less 
pronounced yellowing, but that could easily be due to other factors, as my 
garden soil conditions and microclimate varies widely over the different 
areas.

One thing you don't have to cope with is the New Zealand cabbage tree moth 
('cabbage tree' is the local common name). The caterpillar eats large 
sections out of the leaves, which can make some of the trees look really 
messy.

A couple of tips for people who may want to try these trees in their own 
gardens. They are very shallow rooting when planted on clay soils. I have 
had three trees blow down, which were planted over a heavy clay pan, once 
they got big enough for the wind pressure to snap the roots about a foot 
below the surface. This may be generally true of the root system, but I 
have never dug any up to check. The other thing is that if you do cut one 
down, don't bother to try to burn the wood, it is almost fireproof. I use 
my fallen tree trunks as edging for raised beds. It seems to be taking a 
long time to rot.

Tim Dutton
"Raindrops", Main Road North, Kaitoke, Upper Hutt, New Zealand
(Latitude 41? 5' South, Longitude 175? 10' East)
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