Friday, January 24, 2014

How Windchill Affects Roses

Yesterday, we woke up in Minneapolis to a temperature of -17 F, with a windchill of -36 F . Every TV weather-person in town was wide-eyedly proclaiming the dangerous windchill temperatures, to the point, I'm sure, of scaring the average person, who had to go out of the house to work or school, half out of their wits. In fact, every school district cancelled school for the second time this winter, due to the windchill temperature.  Our most sophisticated local (and national) meteorologist, Paul Douglas, posed in his blog yesterday his rhetorical question of whether they cancel school for windchill temps in Canada?  It's no wonder people start believing that the temperature really is -36 in Minnesota, when -17 is quite bad enough.

Question: What temperature do you think our roses were "feeling" yesterday morning?

Simple Answer: -17 F.  Neither roses nor any other plant experience any temperature other than the actual ambient temperature.  And -17 is plenty cold, thank you very much.

Here's a good quote from a National Weather Service article about windchill:

"Wind chill is the term used to describe the rate of heat loss on the human body resulting from the combined effect of low temperature and wind.  As winds increase, heat is carried away from the body at a faster rate, driving down both the skin temperature and eventually the internal body temperature.  While exposure to low wind chills can be life threatening to both humans and animals alike, the only effect that wind chill has on inanimate objects, such as vehicles, is that it shortens the time that it takes the object to cool to the actual air temperature (it cannot cool the object down below that temperature)."

Here's that whole article

Here's another good quote from a Kansas State University article:

Plants Don’t Care if the Wind Chill Tanks

"When wind chill temperatures plummet, gardeners chafe about their landscape and fruit plants' odds for survival.  Some gardeners worry too much.... Cold can be a killer if people are growing marginally hardy plants or if air temperatures drop well below what's usual where they live.  Hard freezes are particularly destructive when plants aren't fully dormant.  But cold and wind chill aren't the same thing.  Wind chill only affects warm-blooded animals -- including people.  It's an indexed, scientific measure of how wind speed and air temperature combine to impact animal heat loss.... We know, for example, that our heat-loss rate will speed up as the air temperature drops.  The faster the wind is blowing, however, the more dramatic that heat loss is going to be .... Wind chill has no meaning for plants.  Unlike warm-blooded animals, they don't try to maintain a particular body temperature year-round".

And here's that whole article:

Of course, we know that  roses feel the winter cold and die back according to the level of protection afforded them.  And winter-winds do, of course, have an effect on that die-back, desiccating the canes, but the important thing to understand is that wind does not make a plant "feel" colder than the actual temperature, even though it shortens the time it takes for the plant to reach that temperature.

Here's an example: Suppose that the ambient temperature is 35 F and the wind is blowing 30 MPH. According to the chart in the NWS article (above), the wind chill is 22 F.  So are your roses freezing?  Or, better yet, are the puddles in your garden freezing?  Of course not, because the freezing point of water is 32 F.  However, if you go out in your garden without a hat and jacket, you will feel like it is 22, not 35, because of the combined effects of the cold temperature and the high wind on your flesh.

Another example of the effect of wind chill on the human body is to go back to yesterday's -17/-36 situation.  If I go out for a walk, as I usually do in these temperatures, any exposed skin (like my nose) will be frostbitten in about five minutes because of the -36 wind chill.  That is a serious problem, especially for children waiting for school buses or people who have to work outdoors.  Children are notoriously bad at covering-up in cold weather and, thus, it is probably wise to cancel schools (in Canada too).  And, while my plants certainly are not feeling the wind chill, the old Minnesota Rose Gardener certainly is, so he has to dress accordingly in his thinsulate-lined parka and antarctic mask.

The temperature was about -2 and the wind-chill about -15 when this picture was taken.
Cold enough for ya?  It sure was for me!

So, bundle up and make sure your roses get the right winter-protection each winter.  See my blogs "Winter Protecting Your Roses":

and "How Winter Affects Roses":

Jack Falker
January 24, 2014

Saturday, January 11, 2014

Deb Keiser's Reflections on the 2013 Growing Season

The following  is a guest post from Deb Keiser, Rose Specialist at the Virginia Clemens Garden in St. Cloud, Minnesota.  Deb is a Twin Cities Rose Club member and, in my opinion, one of the most knowledgeable rosarians in the country.

In my last "Minnesota Rose Gardener" blog, "How Winter Affects Roses", I described an unusual situation that occurred in 2013:

"Even though our winters are warmer, in terms of extreme minimum temperatures (EMT), they seem to be just as long, or perhaps even longer in certain years, thereby keeping our roses frozen for a longer period of time. For example, our ground (and therefore our roses) stayed frozen into late April or early May in 2013, and we had snow on the ground into early May.  This is 2-4 weeks later than normal. What happened in May, once the ground thawed out, was that the roses had a very hard time getting started and there seemed to be more die-back than usual, even with shrubs that are zone 3 and 4 hardy.... In other words, with a 2013 EMT of -13 (well above the median for zone 5), our roses actually seemed like they had been through a much harder winter.  So it would appear that the length of time roses are frozen, not just the low temperature in a given year, impacts survivability.  After all, if you think about it, frozen is frozen; the only thing that happens with a lower temperature is that the ground freezes deeper and the roses take longer to thaw out and start growing in the new season.  But what happens to them when the winter is so long that they can't start growing again in a timely way?"

Here is Deb's description of what happened in the Clemens garden in 2013, including the loss of 12% of their roses, which is highly unusual for a professionally run garden that uses state-of-the-art winter protection methods. It is eerily similar to what many, if not most, Minnesota rosarians experienced in 2013.

Mid December Reflections on the 2013 Growing Season
By Deb Keiser, Clemens Garden’s Rose Specialist

The weather in April and May 2013 will be remembered as “extreme” and “record-setting” in many parts of the United States. St. Cloud, MN was no exception to this. We broke several long-standing records and experienced extreme weather fluctuations.

To plan for the date that our garden staff will uncover the construction blanket covered roses at Clemens Gardens, I often start watching the forecast high and low temperatures near the beginning of April, with a target date of the week of April 15th as the estimated time for the actual uncovering. With widely fluctuating weather this past April, Mother Nature kept us anxiously waiting and watching for warm weather for quite awhile. On April 11, 2013, St Cloud received 8.7 inches of snow. The high temperature on April 15, 2013 was 36 degrees. We had freezing temperatures every night that week. On April 18, 2013, we received another 9.4 inches of snow and we set a new record for most snowfall in April with a total of 24.4 inches for the month. On April 20, 2013 we set a new record with a low temperature of 16 degrees in St. Cloud.  I knew it would take awhile for the snow to melt with temperatures like that, so I set my new target date for May 1, 2013. Then on April 27th, we had a high temperature of 74 degrees with a low that day of 30 degrees. Crazy weather indeed! April 28th brought us a 77 degree day followed by a couple of days in the low 70’s which made uncovering the roses seem very tempting, except for the 10 day forecast. Just when we thought it was finally safe to uncover the roses, an early May snowstorm dropped a record-setting 18 inches of snow on parts of southeastern Minnesota. In St Cloud, we were fortunate not to get snow but we did have high temperatures in the low 40’s, a low of 28 degrees, and ¼ inch of rain from May 1st thru 4th. With a rose pruning day for volunteers scheduled for the evening of May 6th, a high temperature of 72 degrees that day and 70 degree temps forecast for the week, I decided that we could finally uncover the roses. As luck would have it we experienced freezing low temperatures the following weekend, followed by a high of 95 degrees two days later. Only in Minnesota! If you don’t like the weather, just wait awhile and it will change!

Here is a re-cap of the 2013 rose growing season at Clemens Gardens, highlighting some of our achievements and some of our misfortunes.

Misfortunes –

When uncovered, the tender roses in the Virginia Clemens Rose Garden looked alive but not leafed out as in past years. This was probably due to the late cold temperatures in April and May, prior to uncovering them. This made for a late first flush – July 4th weekend, as compared to a Memorial Day weekend first flush in 2010, a June 20th first flush in 2011, and a mid-May first flush in 2012.

Our pruning season started late, our weather warmed up fast, and it was off to the races to try to get over 1,800 roses pruned before they were totally leafed out. With only one assistant and a handful of volunteers, we were still pruning roses in mid-summer.

We lost 140 hybrid tea and floribunda roses in our 1,200 rose Virginia Clemens Rose Garden, or about 12%. Fortunately, most of the roses were older roses that were in the gardens prior to when I started working here in 2004, and some were donated packaged roses from 2006 and 2007. The roses were probably weak to begin with from the 31 days of 90 plus degree heat and drought conditions in July 2012. The late cold weather after uncovering them did not help either.

Due to the late start to the season our Bob’s Mix fertilizer was applied much later than normal. The weather at application was hotter and drier then usual. We did not see a big growth spurt in the roses until we had rain and cooler temperatures late in the season. The roses were much shorter than normal and did not produce as many blooms.

Our Award of Excellence (AOE) miniature rose trials entries for 2013 arrived the week of April 25, 2013 and had to be repotted and grown in the Munsinger & Clemens Gardens’ greenhouse until it was warm enough to plant them outdoors. They were moved out to the AOE trial garden later than normal, which meant less time for the AOE Evaluators to evaluate them.

Achievements –

The long cold spring gave our 95 new roses from Weeks Roses, our five shrub roses purchased from Twin Cities Rose Club’s fundraiser, and our sixteen 2013 AOE trial miniature rose entries plenty of growing time in pots in our 10,000 sq ft greenhouse.

We received plenty of moisture early in the 2013 season to get the uncovered roses and hardy shrub roses started growing well in the garden beds.

The shrub and Old Garden roses that we moved from UMORE garden in October 2012 and planted in our lower rose garden, came through the winter very well with only compost for winter cover. I was pleasantly surprised at the winter hardiness of the zone 4b & 5 roses – four ‘Double Knock Out’, seven ‘Carefree Marvel’, and two ‘Salmon Impressionist’. All of the shrub roses from UMORE grew and bloomed well during 2013. The ten plants of ‘Winnipeg Parks’ which were planted on the rock walls bordering the front and south side of the Virginia Clemens Rose Garden were constant bloom producers. I heard many visitors commenting on their beautiful large pink flowers. The OGR divisions off of the UMORE “mother” plants experienced nice growth and may bloom for the first time in June 2014. I look forward to seeing all of the spinosissima, gallica, alba, & moss roses in bloom.

The shrub roses in our Lower Trial Rose Garden proved their winter hardiness by surviving the winter with only a 4 inch layer of rice hull mulch and snow cover for winter insulation. These include ‘Pink Home Run’, ‘Carefree Sunshine’, ‘Peppermint Pop’, Northern Accent roses ‘Ole’, ‘Lena’, ‘Sven’, and ‘Sigrid’, Easy Elegance roses ‘Little Mischief’ and ‘Sunrise Sunset’, ‘Carefree Wonder’, ‘Como Park’, ‘Thrive!’, ‘The Charleton’, and Kathy Zuzek’s trial roses. Blackspot was not a problem in the Lower Trial Garden, even though the rice hull mulch had been wintered over from the previous season. The shrub roses were very disease free this season.
We replaced most of the soaker hoses in the Virginia Clemens and Upper Trial Rose Gardens with new ¾ “ Osmile double-thick wall soaker hoses with a lifetime guarantee. The hoses were put in place prior to the hot, dry weather in July and August. They worked very well during the season with much better water output than the older hoses. The best thing was no more fixing broken soaker hoses. We will replace the rest of our soaker hoses next summer.

Although it was later than normal when we planted our new potted roses from Weeks, Twin Cities Rose Club, and AOE entries outdoors, they transplanted and grew well. Many of the plants were already in bloom and were good sized plants when planted outdoors. I was especially impressed with the three test roses that Weeks sent us. All three plants grew well and their blooms quickly became noticed by visitors. The large golden orange long-stemmed blooms of hybrid tea rose ‘Good As Gold’ and the large fragrant bright yellow old-fashioned blossoms of grandiflora rose ‘Happy Go Lucky’ seemed to put on a constant display. Both were very disease resistant. Although grandiflora rose ‘Coretta Scott King’ with its beautiful long coral and white buds and disease resistant foliage did not bloom as much as the other two test roses, its big clusters of blooms were very long lasting.

In early July, we purchased 16 very nice large potted hybrid tea and floribunda roses from Linder’s Greenhouse during a 50% off sale and 24 own-root hybrid tea and floribunda roses on sale from Roses Unlimited. They performed well and added many older varieties that are new to our gardens. The three plants of floribunda ‘Oh My!’ with its dark velvet red blooms and the bright red blooms of hybrid tea roses ‘Olympiad’ and ‘In the Mood’ from Linders Greenhouse put on a good display along the Upper Trial Garden walkway through the Clemens Rest Area Garden. The two pink bloomed ‘Sexy Rexy’ floribunda roses and the two ‘Estelle’ hybrid tea roses with their florist quality russet blooms reversing to yellow drew many comments from visitors to the Virginia Clemens Rose Garden. Both were purchased from Linders. We were sad to hear of the closing of Linder’s Greenhouse. They were a generous donor of many good quality roses to our gardens and a good source of quality plants and shrubs for Minnesota gardeners. They will be missed!

We only had one week of 90 plus degree weather in mid July and another week of  90’s at the end of August. Unfortunately, it was during the MN State Fair. Most of our July, August, and September temperatures were in the mid 70’s to low 80’s, which made for wonderful working conditions at the gardens. Our rainfall was below normal but the new soaker hoses worked well. We fertilized the roses with Alaska Morbloom fertilizer 0-10-10 after August 31st and the roses continued to bloom and grow.

In September and early October, we gave the Virginia Clemens and Upper Trial Garden roses doses of potassium sulfate 0-0-50 to help ready them for winter. I chose potassium sulfate with the hopes of lowering our soil PH from almost 8. We also treated areas of the Virginia Clemens Rose Garden, where our roses were experiencing growth problems, with fast-acting sulfur (calcium sulfate) also with the intent to lower the PH in those areas to improve growth for 2014. I will be checking our soil PH again next spring and adding amendments as necessary to correct our PH.

Winter came early with cooler than normal temperatures in mid October, so we started our winter protection process of cutting back the tender roses to 8 inches of height. This allows us to cover the rose beds tightly with insulated construction blankets. We mulched the roses with two large scoops of finished compost over the crown and extending out to the sides of the rose plant.  With temperatures threatening to drop into the teens at night, we applied insulated construction blankets to the rose beds in the Virginia Clemens and Upper Trial Rose Gardens on November 7th and tucked our roses in for their long winter’s nap a few days earlier than in past years. So far this winter, we have had a good amount of snowfall to add additional cover to the rose beds.

Now we plan for next season with the hope of an earlier start in the spring with less winter damage, followed by adequate rainfall and warm sunny days for good growth, and an insect and disease free season. One can only hope that Mother Nature is good to Minnesota gardeners next year!

As always, let Deb and me know what you think.