CO-Horts

CO-Horts

Monday, May 13, 2013

Ah, that crazy Colorado weather strikes again!

Posted by Andrea Cummins, Douglas County Extension


Once again, the schizophrenic Colorado climate has created havoc for many of our trees. As I see photo after photo (and lots of samples too) of evergreens that have “suddenly” turned brown, I think the finger of blame has to be pointed at Mother Nature. Although humans who fail to water regularly and effectively in the winter can share this blame.

Spruce showing varying amounts of drought and frost damage

With the past two years of drought, the scorching hot summer of 2012, and then the unusual cold temperatures of early April, the trees have taken a pretty big hit. Even with winter irrigation (we ALL water in the winter right?) evergreen trees are showing pretty serious winter desiccation symptoms. Add to this existing drought stress the extreme cold temperatures of early April (right when the trees were starting to de-harden from winter), and you have a perfect scenario for ugly, brown trees virtually overnight.

Young Ponderosa pine suffering from winter desiccation and cold damage

Winter desiccation occurs when there is low humidity, no snow cover, and windy weather. The plants loose more water through their needles then they are able to take up through their roots. When these dry conditions continue for years on end, as they have recently here along the Front Range, the trees become more and more stressed. The fine roots hairs (those that take up the water) can die in dry soils and this makes the problem worse. This is why winter watering is so critical – it cannot solve the problem of low ambient humidity and transpiration, but keeping soil moist at least gives the trees a fighting chance during those warm winter days. Desiccation tends to appear more frequently in exposed and windy sites, southern and western exposures, in years with little snow cover, and on younger plants. However, many of the photos we are seeing in the office are of mature trees – so they are not immune to this problem. Don’t think that you don’t need to water mature trees in the winter. Even though they have farther reaching root systems, they also have bigger canopies, and a lack of soil moisture will affect them as much as it does immature trees, sometimes it just takes longer for the symptoms to appear.

The cold temps of early April shocked the plants when they were starting to reawaken for spring. Trees “harden” their tissues for survival during cold temps and then “de-harden” for the growing season. When temperatures fluctuate to the extreme, as they did here in early April (and do frequently in our crazy climate) the trees cannot adjust quickly enough to protect their needles from the freeze. The buds are often more protected (as buds are the tree’s hope for the future), and the tree will send out new growth. We see this happening now with many of the deciduous plants that were just starting to leaf out and got nipped. The new leaves died but the buds were undamaged and are producing new growth. Hopefully this will happen for the evergreens as well. 
Austrian pine in front will likely recover, although it will lose the brown needles. The spruce behind may be a goner. Pine is toward the bottom of the hill and therefore gets more moisture as compared to the spruce at the top of the hill. 

So what to do now? Wait and see what happens. While the needles may have died due to the extreme cold, the buds themselves may still be healthy and able to push new growth. It is just too soon to tell. The ability of the tree to recover will be directly tied to how stressed it was going into the April freeze --again with the winter watering. Those trees that were already in extreme drought stress will be much less likely to have the energy reserves to recover. Put your pruners and loppers away for a few more weeks and wait and see what your trees do, with a bit of kindness from Mother Nature (think 70 degree weather for a while) and regular irrigation, they may snap back. 

7 comments:

  1. Although humans who fail to water regularly and effectively in the winter can share this blame.

    ReplyDelete
  2. do you have an update on what you're seeing for evergreen's now that the summer is over? Our HOA is wanting us to cut down our brown arboritae bushes however with regular watering thru the summer they are now brown arboritaes with green highlights! and clearly trying to pull thru. I'm looking for some back-up to my claim so we don't have to take them out after 8yrs of looking wonderful:-/

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