A Lost Hope?

Posted by: Curtis Utley, Jefferson County Plant Diagnostic Clinic

On a recent tree evaluation visit I discovered more fallout from the historic polar vortex freeze event in November 2014. Many of my contemporaries said we would continue to see more damage in otherwise apparently unaffected species and sure enough, now two seasons later, green ash trees are pushing off large sections of damaged bark. 

Bark loss from Callery pear observed in 2015

This damage and the resulting recovery is similar to what we are seeing on ornamental pears but the symptoms have been delayed do to the difference in bark thickness of green ash. The South or Southwest facing sides of green ash trunks and branches had not gone dormant when the freeze event occurred and these portions of the vascular cambium were killed. 

Green ash with loose bark on the south side of the tree.

White ash trees were not affected but green ash trees growing in warm locations, in this particular case street trees growing on a south facing slope show considerable damage. 

Thinning canopy and dieback on ash from the November 2014 polar vortex freeze event.

The marginal cambium that did not freeze is now trying to grow over the damaged section of trunk wood and is pushing the dead bark off in its attempt to close the wound. Another concerning symptom that is explained by this freeze damage is the thinning canopy and decreasing growth increments in affected trees. 

Ash tree attempting to close wounds from freeze injury.

We have had two cool wet springs that should have resulted in fantastic growth in green ash and to see the opposite has had me concerned. The elephant in the room anytime we discuss symptomatic  ash trees is of course the possibility of finding emerald ash borer, especially in trees that are losing chunks of bark, have thinning canopies, and dying crowns. The difference between freeze damage induced bark loss and bark loss as the result of the exotic emerald ash borer is the absence of a zig-zag or meandering pattern visible both on the loose pieces of bark and exposed wood caused by EAB larval feeding. Learn more about emerald ash borer at: eabcolorado.com

Emerald ash borer feeding (photo courtesy of University of Minnesota Extension)

The Cold Frame Corner (Part II)

Posted by: Susan Perry, Master Gardener in Larimer County

Well, a lot has happened since my last blog post.  All seemed to be going well in October/early November, although we noticed that the temperature in the lettuce/spinach box was no warmer than the outside air temperature.  Further study revealed the first (of several) flaws in our plans – the R-value of all the materials used in the cold frame really matters.  So, culled (bent) wood that doesn't have tight corners plus polycarbonate tops weren't going to do a darn thing toward keeping temperatures in the cold frames warm enough. 

 

Lots of good spinach and lettuce

So toward the end of October, we decided we had to revisit the use of rigid construction insulation to line the boxes.  We did that, but still no joy because (we finally figured) that all the heat was escaping via the polycarb.  Even though it is twin-wall polycarb, it just doesn't have any insulating power.  Yikes!  By now, it was Monday November 10^th & the forecast said weather was moving in – a “polar vortex” that would cause daytime temps in single digits and nighttime temps below zero.  Uh oh ….. when I left the house for a salvage company east of Loveland that had some Styrofoam on Craigslist, the temperature was in the 50s.  By the time I was loading a few pieces of Styrofoam into my car, the temperature had dropped at least 15 degrees and the wind had picked up, and by the time I got home, it was even colder. 

 

Beets inside and outside the cold frame.

We shifted into almost panic mode – we needed to do whatever necessary to keep the lettuce/spinach alive.  The ground around the carrots, beets, & leeks would not freeze in a week of cold temps so we focused on the two lettuce/spinach boxes.  We lined each box with two strands of incandescent indoor/outdoor Christmas lights, covered the lettuce/spinach w/floating row cover, put the polycarb tops on, put a flannel sheet, then a quilted moving blanket, then a sheet of plastic weighed down with rocks.  Then we went inside.

 

Using Christmas lights to increase the heat inside the frame.

The two strands of Christmas lights per box worked.  At the highest, before we figured out how to make best use of the lights, the temp in the box got to 70 degrees.  We needed to be sure the air temp didn’t drop below about 30 degrees.  With the lights, it didn't seem like a precise approach, so we just made sure to keep the cold frame temps in the mid-30s.  There were a couple of middle-of-the-night temperature checks.  Finally, we noticed a pattern:  the box would heat up rapidly till it got close to it’s maximum temperature, then even with the lights still on, it just wouldn't get warmer; and when we unplugged the lights, the temp would drop to 50 degrees, then take 8 -10 hours to get down to 39 degrees.  This led us to conclude that we could plug the lights in before going to bed & unplug them in the morning.  Even better was when we got the lights on a timer, because we could have the lights turn on an hour or two after we went to bed & go off an hour before waking and all would be well.

The brutal cold finally moved east so we were able to make some additional modifications.  We’re not keen about using rigid insulation, but we made tops for the beet & carrot boxes just until we got something better worked out.  And the leeks …. well, we never got them protected at all & despite having the most cold tolerant variety possible, well they were toast (or should I say mush?).  We've salvaged what we could, sautéed & froze it for future use in soups.  But that was a disappointment, but not really a surprise.  The height of the leeks, even if we trimmed the tops off, was still an obstacle to constructing a decent cold frame that would work.

 

Root crops during "polar vortex".

Where are we now?  We’re testing space blankets in the lettuce/spinach boxes instead of floating row cover plus flannel sheet plus quilted moving blanket plus plastic sheeting.  So far, it looks like it’s a great alternative.  The space blanket reflects the heat from the (now) single strand of Christmas lights in each box.  We've devised wickets for each box & have tried to make tabs on the space blankets so we can attach them to the wickets and slide them open & closed in morning and evening.  Attaching the space blankets to wickets makes them easier to deal with on windy days, and means we can just leave them in the box, slid open, all day before sliding them back in the evening when we close the cold frames up.  We also were able to purchase proves for our wireless thermometers so that the foil on the rigid insulation would not disrupt the signal. 

 

Adding wickets and space blankets to the cold frames.

We still need to make wickets for the beets and carrots so we can use space blankets in those boxes.  We also need to get a better sense of what combination/number of Christmas lights are necessary in the lettuce/spinach boxes to keep the temps between 35 – 45 degrees regardless of how low temps go in the next “polar vortex”, which is sure to come back.  We also need to harvest all of the remaining root crops (carrots, beets, & leeks) that were outside of the boxes – always planned to be harvested first while the cold frames would be harvested last.  We’re just hoping that there’s something to salvage …. we’ll see.

 

We survived the cold!

So, except for the leeks, the experiment is working.  And we already have ideas for future modifications to improve the process.  Just too bad the “polar vortex” arrived so soon, before we were really ready, but that’s the way it goes sometimes.

Next week:  home-made ravioli using spinach from our garden!  I’ll let you know how it turns out.

Frozen

Tony Koski
Extension Turf Specialist

No, Elsa, this isn’t about you..

A very frozen dandelion...still alive

Some have asked, on the heels of the recent “polar vortex” (not really…it was just a sign that winter is coming...read about that here) and temperatures hovering near zero, about how the early and abrupt cold snap might affect turf pests – weeds, fungi, and insects? The short answer (in case you want to leave now and hear Elsa sing…again) is that it likely had little effect on any turf pests – and is unlikely to affect turf pests in 2015.

There were plenty of signals (fewer hours of daylight, cooler temperatures, frost) this fall to encourage our lawn grasses (the good ones…and the perennial weedy ones as well) to ready themselves for winter. Insects that overwinter as adults, larvae, or pupae likewise were readying themselves for diapause (insect “hibernation”). Perennial weeds like dandelion, thistle and beloved bindweed were preparing themselves for winter dormancy well before last week’s chill arrived. The spores and mycelium of fungi (it was a good fall for powdery

Knotweed (Polygonum aviculare), a summer annual,
still alive after subzero temperatures!

mildew and rust on turf) are so resistant to temperature extremes that the arrival of 0 F went unnoticed by them – so they will be back next year, without question.

Seedling downy bromegrass (aka cheatgrass) thriving in
our chilly pre-winter cold snap

Even the seedlings of our winter annual weeds - species that germinated this past late summer/fall and will complete their life cycle in the spring – appear to have been completely unaffected by the week of extreme cold. The henbit, annual bluegrass, chickweed and cheatgrass I’ve looked at in the past few days appear perfectly healthy. So, I'm sorry to dash any hopes you had about any potential benefits that the recently departed cold front might have had on the pests in your lawn. They really didn’t notice. If you had any hopes of the misnamed polar vortex eliminating some of next year's turf pests, all I can say is … let it go…let it go……..

Aw Snap! (Cold snap, that is.)

Posted by: Alison O’Connor, Larimer County Extension

As weather forecasters were predicting our cold snap that we’re currently suffering through, I began thinking about our outdoor plants and wondering if they had hardened off. Others thought the same thing, because a recent listserv had chatter of comparing this cold snap to the Halloween Freeze of 1991. In short, the spring of 1992 proved to be fatal to many trees and shrubs, particularly Siberian elms. 

Nerd alert! Taking photos of plants in sub-zero weather.

I don’t have any elms in my landscape, but I do have many roses. And my curiosity was spurred this week by a woman who emailed asking what she could do to protect her roses. After all, ours were both still blooming and the leaves hadn’t dropped. It seems all of these things (below-normal temperatures, tender green tissue and blossoms) are pointing to one thing—likely major dieback and possibly plant death come spring 2015.

Boy howdy. That stinks. I love my roses.

I consulted with Larimer County Master Gardener and Rose Guru, Roger Heins, on his take on the subject. He expressed similar sentiments, unless people did some extra preparation (he did). I did not. But here are his recommendations for future consideration:

1. Two or three days before the cold weather sets in (and when daytime temperatures are above freezing), deep water your roses. Actually, take the time to water all of your trees and shrubs.
2. After the first two initial temperatures of nighttime temperatures below 30 degrees F, but before a hard freeze (<26 degrees F), pull bark chip mulch (or soil) around the base of the roses. If there is still foliage, don’t make the bark mulch too heavy…wait until leaf drop.
3. If you have roses with long canes (one of my “shrub” roses is over 8’ tall), you can prune the canes back by 1/3 to reduce injury from snow, ice and wind.
4. If you have blooms on the plant, remove these, as they can collect snow and ice and cause the canes to bend or break.
5. After the roses go dormant and lose their leaves, increase the mulch depth around the base of the plants. The rule of thumb is to mulch about 6-8” up the canes. As the roses come out of dormancy in spring, remove the mulch.
6. If you have the time and ability, you can wrap the roses in burlap.

Roses in bloom on 11/12/14.

Remember, snow isn’t a bad thing—and can act like an insulator.  But we generally can’t rely on continuous snow cover through the winter, so extra precaution is a good thing. Because my roses are an important part of my landscape, I will mulch them once I can stand to be outdoors for longer than 30 seconds. And I’ll put it on my schedule to water them once we get those glorious warm winter days. 

Snow can be a great insulator for roses.

Until then, I’ll be anxiously awaiting the arrival of spring to see how this polar vortex affects our landscapes. And keeping my fingers crossed (inside my mittens).

Not a rose! But the red arils on burning bush are beautiful.