Re: CULT: question - frost heave

I read in some seemingly credible source (which I no longer recall) that iris stop growing when the soil temperature gets below 40 degrees (F). By that theory, it's not so much the frost or freeze that ends the growing season (assuming the frost isn't so harsh it kiils the foliage) but the temperature over a long enough time to get the soil that cold.

The rule of thumb I hear most often about planting is 6 weeks before the first freeze, as some here have just said, but obviously some plants planted before that die and some planted after don't. That first freeze is said to average around October 1st here. We had a frost, with ice around sprinklers and such, in this area in August this year--didn't happen at my house, but here and there around me. Since then things have been fairly normal for this time of year, with the irises still growing.

One thing I've done to try to get late plantings to grow better before they run out of time is to put rocks around the rhizome and mulch (mostly broken willow twigs) over the rhizome itself on the theory that it will keep things from getting as cold at night. Another thing has been to pour warm water over the rhizomes in the morning, raising that soil temperature some. I have cold nights here, typically down into the low 40s this time of year, even if its warm during the day. Don't know if either of these things really helps; it's all based on theory.

There has been discussion here in the past of putting rocks or bricks over rhizomes after the growing season to prevent frost heave. I'll probably do that with the new plants, but I haven't decided about the ones I put in last year.

Kent
Sanpete County, Utah
zone 4/5
some trees down the street are changing color, the mountains are in full fall colors
Queen Dorothy still blooming



Linda Mann wrote:

For those of you who garden in areas where frost heave of newly planted
rhizomes is a problem,

how late before the ground freezes can you usually safely plant?  Six
weeks?

Back when the winters were colder here, the ground wouldn't usually
freeze until around Christmas.  Sometimes earlier.  Not at all last
winter.

--
Linda Mann east Tennessee USA zone 7/8
East Tennessee Iris Society <http://www.korrnet.org/etis>
American Iris Society web site <http://www.irises.org>
talk archives: <http://www.hort.net/lists/iris-talk/>
photos archives: <http://www.hort.net/lists/iris-photos/>
online R&I <http://www.irisregister.com>

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