Re: CULT: FAQ: fighting late freezes-long

Margie asked for ideas to protect her irises from late spring freeze
damage, so here's a list of various things I've done that work, more or
less, plus some ideas.  They goal is to protect actively growing irises
in late winter/spring when air temperatures drop below about 25oF.  If
it drops below 15o after lows have been above freezing for a week or so,
these methods may not be enough protection.  If it drops much below 30oF
after stalks are showing, I haven't found anything satisfactory.  Neil
Mogensen suggested a giant fan to keep the air circulating, so maybe if
you have access to a spare airplane propellor....

PLANT BED COVERS
I have used everything from blankets & bedsheets to plastic, but have
had best success with non-woven synthetic fiber tobacco plant bed
covers.  These are lightweight, relatively inexpensive, and don't
require supports to hold them off the plants.  Synthetic plant bed
covers come in a variety of thicknesses and tightness of weave that
provide different levels of protection. I posted a photo this spring
called something like 'resistance is futile'.  The drawback to using
these covers is that by the time you really need to be using them (6 to
8 weeks before bloom), temperatures are going up and down so much that
they can't be left in place for the warm spells.  They tend to trap heat
and the extra warmth during sunny days will just encourage more tender
growth.  I used to cover and uncover with every front - a real nuisance.

WATER BOTTLES
Stacking a lot of 1 liter cola bottles filled with water around the base
of the plants provides some protection, especially for cultivars that
aren't especially prone to foliar damage but are prone to showing later
damage to terminal growth of the flower stalk (dead and rotten, stunted
stalks, deformed flowers).  The water acts as a heat sink, storing
warmth during the day and releasing it at night.  I have a photo that I
will post.

MULCHING WITH SOIL
This has proven to be the easiest (also LEAST effective) method of
protection.  Some cultivars rot when buried in soil (I figure that just
gives them an early funeral with a decent burial <g>), but those that
don't rot seem to do better in the late freezes here.  I don't bury them
deep, just make sure there is a bit of soil on top of the rhizome.  My
soil is full of gravel, which makes it excessively well drained and also
makes it warm up faster in the spring than, for example, heavy clay.
Because of the early warming, late freeze damage is more likely to occur
here, but the gravel also makes it safer to cover the rhizomes with a
bit of soil.  Some folks have posted that they mulch with sand or small
gravel.  I haven't tried that, but it might be an option in heavier soil
that doesn't drain as well as mine.

MULCHING WITH MULCH
This is what you asked about & is the subject I know the least about.
Some cultivars can probably tolerate mulch directly over the rhizome,
but I haven't experimented much in this area.  One year, just to see
what would happen, I mulched some rhizomes with pure horse manure,
covering the entire rhizome.  Most of them died (no surprise) but not
all.  One of our club members has a small commercial nursery and they
used to mulch heavily with fresh sawdust (coarse sawdust from a
sawmill), putting it right up to the fans.  They said that this produced
the nicest rhizomes (big and healthy).   One advantage to sawdust is
that it takes a lot of nitrogen to feed the decomposing bacteria and
fungi, which ensures that you less likely to have excess nitrogen
causing lush, freeze damage prone irises.

NUTRITION
This is another area where I don't have much useful to suggest, but
boron, magnesium (trace elements) and calcium are important in the
growth, maintenance, & repair of actively growing tissues.  And Cooley's
(?I think) has found sulphur is also important in rot prevention (i.e.,
plant stress reduction?).  Different regions of the country are
deficient in different trace nutrients, plus different plants require
different amounts, and high levels of all trace elements are toxic.
Legumes, alfalfa in particular, need a higher level of boron than most
other plants, so adding a bit of alfalfa pellets for fertilizer now and
then should be a safe way of making sure boron levels are adequate.
It's easy to add too much if you try to use something like Borax - one
tablespoon per acre can be too much!  I have been adding a lot of
crushed limestone the last couple of years, just to be sure the irises
have enough calcium and magnesium.  In our humid climate, it is released
slowly, so shouldn't raise the pH too much & is easier to stay in a safe
range than with something like slack lime.  Check with your local
extension agent or a comprehensive soil science reference to see if
there are other trace element deficiencies in your area.  Also, be sure
not to over fertilize with nitrogen.  Just to be safe, I don't apply
fertilizer containing nitrogen in spring until AFTER irises have started
blooming.

Whew - hope there is something in all that you can use Margie.
--
Linda Mann east Tennessee USA zone 7/8

Tennessee Whooping Crane Walkathon:
<http://www.whoopingcranesovertn.org>
American Iris Society web site <http://www.irises.org>
iris-talk/Mallorn archives: <http://www.hort.net/lists/iris-talk/>
iris-photos/Mallorn archives: <http://www.hort.net/lists/iris-photos/>




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