soil temperature

Dear Friends,
	I've been curious about the function of soil temperature with respect to
siberian performance; I can't think of another obvious factor in why
siberians are generally not vigorous in southern California, while doing
beautifully in Oregon and reasonably well in central CA. The west coast has
wet winters but even in Oregon, at least near the big iris growers, I
suspect the soil rarely freezes (I'd love some information from gardeners
in that area). In fact the iris seem to die off most during the winter
season here, presumably to some root rots; But Oregon and more northerly
parts of CA are wetter (well, perhaps not today), and the sibs don't seem
to die off during dormant season.

	For instance, one approach I've tried was to plant the sibs on the north
side of a hedge - so for four months, there is no sun on the soil there. I
did measure it a few degrees cooler than soil in the rest of the garden.
But it doesn't seem to have been enough to change the performance of the
plants. (well, after a while the oleander roots got into the bed...)

	I'm wondering if some of you would like to gather soil temperature data; I
can put it all together, though whether with casual observations we can
have enough accuracy remains to be seen. Especially useful would be from
people on the west coast; but data everywhere would be useful, especially
during the time of growth and bloom in the spring. After all, when the
spring warms up too quickly, bloom height is said to diminish, as for
example at the National in Virginia (was that 91? somewhere around then).
Make a note of the temp coupled with what is happening with growth and
bloom of the sibs. If you have some areas mulched, and not mulched,
comparison of those temps would be useful.

	I'm using a dial thermometer with about a six-inch stem; and I insert it
all the way. That seems like a good depth to concentrate on. This is a
pretty accurate instrument my father used in his darkroom. Similar shaped
soil temp thermometers are for sale but hardly of the accuracy; so it might
be a bit expensive to get something good. No doubt that will eliminate many
of you. 

	Of course the soil heats up during the day, and cools off at night. And a
colder night will make morning readings colder; a warm day make afternoon
readings warmer. A layer of mulch, such as might be on the siberians, might
mitigate but not eliminate this fluctuation. One would have to take
readings always at the same general time. But you can see, taking readings
once a week might not be close to the average - you might hit it all on
cold days, or warm. So we might not have much useful information; but
clearly most people are not going to take readings every day! Still, it
would be better than nothing.

	No need to communicate unless you want to (directly to
mzarky@earthlink.net) - just start recording temperatures (well, not if the
ground is frozen!). I'll put out a call in the summer to collect the first
part of the results.

	But if there are thoughts on how to improve the scientific aspects of this
(someone knows of affordable thermometers; thoughts on frequency of data
collection, etc) we can discuss it in the group.

	Thanks.



BTW, I don't want to tease, but yesterday I noticed the first bloom stalks
forming (on one ridiculously early seedling - it has bloomed on Mar 17
several times. that's about 2 weeks earlier than other seedlings). Scout's
honor.







	


Michael Zarky
10963 Citrus Drive
Moorpark, CA 93021 USA

 

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