Cold snap alert: cover those plants

By Carol O'Meara, CSU Extension Boulder County

The cold snap predicted for Thursday and Friday is not going to be kind to the garden.  Yes, we can use the rain, but the snow and below freezing temps means gardeners should get ready to cover up.  Grab tarps, plastic sheets, buckets, and keep your therapist on speed dial for the inevitable call to cry on their shoulder; this freeze is catching us after we’ve planted.

Tender vegetables like tomatoes, peppers, eggplant, cucumbers, napa cabbage, or squash should be capped with an extra bucket, coffee can, Mason jar – anything that will trap the heat from the soil.  If the planted area is too large for individual buckets, set up a tent to cover the plants with plastic.  The trick is to trap the soil heat, so ensure that the plastic reaches the ground on all sides.  Weigh it down so the wind doesn’t blow it to Kansas and keep the plastic from touching the plants you’d like to protect.

Potatoes, onions, beets, and other root crops nosing up from the soil will be fine under a thick, warm blanket of mulch.  Pile the straw or grass clippings up over the plants to keep them snug under at least six inches of mulch.  You can uncover them after the freeze is over.

There’s not much we can do for the trees but if you have smaller perennials or roses you’d like to protect, swaddle them in plastic as well.  If possible, pull containers into the garage to protect them or cover them with buckets or plastic.  To keep pots from freezing, group them close together and stack bales of straw around them, then cap them with a blanket or tarp.

Make sure that you uncover the plants as soon as the cold snap passes by; things heat up very quickly under plastic and you don’t want to steam cook your plants.

 

Frozen 2: The tree edition

Posted by: Jane Rozum, Douglas County Horticulture Agent

It’s a bad omen for plants when the weather changes from the relatively mild temperatures we received in October and early November into the flash freeze the Front Range of Colorado experienced the week of November 10, 2014. Plants that weren’t snow-covered and subjected to the bone-chilling winds and below zero temperatures were the worst-hit.

We’ve heard from Tony Koski on the effects of the November ‘Polar Vortex’ on grasses and weeds; Alison O’Connor reported on the plight of roses subjected to the extreme cold. What about those plants that live more than a few feet above ground? What about the trees?

In a typical year, landscape plants can handle the below zero temperatures we routinely receive every winter.  However, the biggest problem with this year's November chill was timing. Plants acclimate well to slowly- declining fall temperatures as we approach winter. When plants experience a rapid drop in temperature following mild weather which doesn't allow for proper hardening,  significant plant tissue damage may result.

We are already seeing the effects of this cold snap on our evergreen trees and shrubs. Austrian, Bosnian, and Norway pines and other non-native evergreen trees are exhibiting brown tip foliage, especially on the south, east and west sides of the tree. The north sides of trees may exhibit less damage because that side of the tree likely acclimated to a greater extent than the sides more exposed to full sun.  Brown, brittle buds, if present, may indicate severe cold injury and death of the growing point.  

Deciduous trees were affected by the cold-snap as well. Some trees never dropped their leaves because the cold-snap interfered with formation of the abscission layer that allows the leaves to fall from the trees. Retention of leaves by deciduous plants in the fall is called "marcescence"; leaves die and wither, but do not fall from the tree. For some tree species like oaks, this is a normal, genetically built-in occurrence. Many of our maples and ornamental pears exhibited marcescence because of the November freeze. This leaf retention won’t hurt the tree, but with the leaves still present, heavy wet snow may cause excessive snow loading and lead to broken branches. The full effect of the November freeze on deciduous trees, however, may not be exhibited until this spring and beyond.

Calllery Pear with  marcescent leaves



What can one do about potential damage caused by this rapid onset cold weather?  CSU Extension recommends winter watering trees every so often when we get relatively warm days (40-50°F) and there isn’t any snow cover. A mulch ring around trees, especially around newly planted trees, is always a good practice. No fertilizers should be provided during the winter season.   At this point, we’ll have to wait and see what happens this spring with our woody plants.  

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……..