Re: CULT: Sinking irises

From: Bill Shear <BILLS@hsc.edu>


>So today I noticed that some rhizomes are deeper in the ground.......I'd say
>covered by 1" of soil.  I would think that this was a settling process except
>that its not all the irises in a given area.
>
>Is it possible for the roots to pull the rhizome down in the ground as they
>begin to form?

Some plants do have contractile roots that pull the bulb or crown of the
plant deeper into the soil as they develop.  I think this happens in some
bulbous irises, but probably not in rhizomatous ones.

Think about the opposite possibility--that the soil level has gone up.
Earthworms and insects are continually churning the soil and bringing lower
layers to the top.  Thus a stone, for example, will seem to slowly sink
into the ground over the years.  What's actually happening is that the soil
is being excavated from beneath it by earthworms and piled on the top of
the ground around it.  Darwin studied this more than a century ago in old
graveyards in England, to quantify the amount of soil moved per acre per
year by earthworms.  The year of placement of the stones was determined by
the dates carved on them; older stones had "sunk" considerably further into
the ground.  He came up with some fantastically large figure, demonstrating
how unstable the soil surface can actually be.

Also, do you cultivate?  This could have a similar effect.

All in all, nothing to worry about.  Iris rhizomes will seek their own
level if they get buried.  You probably have gotten new rhizomes in the
mail that were "elephants" that is, with a long, trunk-like appendage
opposite the fan.  These were new increases from buried parent rhizomes
which first grew rapidly to the proper depth, then expanded into typical
rhizomes.  I have had shoots reach the surface from rhizomes buried
(accidentally) as deep as ten inches.

The greater danger is probably for most of us not planting deeply enough to
allow quick root establishment.  In cold climates, shallow planting makes
rhizomes more likely to be heaved out of the ground by frost.

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<bills@hsc.edu>

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