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...because all the best garden advice is local

April 12, 2012
Nature Turns a Cold Shoulder
Greetings!

  Veronica in front of her crabapple in bloom 

Well, this week we saw the down side of all this unseasonably warm, gorgeous weather. I've been enjoying the explosion of flowers, like everyone else. Tuesday morning, much to my amazement, I spotted dwarf bearded iris blooming, about 5 weeks ahead of schedule. I had to wonder, "Is this April or June?"

   The answer arrived Tuesday and Wednesday nights: It's definitely still April. Over the last few days, different parts of the states have been peppered with freeze warnings.

   Fortunately, looking forward into the next week, we're not not likely to be experiencing any more frosts, though it will get close. Still, we're not out of the woods yet. I had a good chat with Dr. Paul Domoto, extension horticulturalist at Iowa State, about the impact of the frosts. He reminded me that two years ago, we had a damaging frost in May on Mother's Day!

 

Yours in frosty gardening,

Veronica Lorson Fowler  

 
How Bad Was The Damage?

 

Dr. Domoto said it's hard to guess, because there are so many variables involved, and different pockets of the state had different temperatures.

   The bottom line, however, is that most home gardeners don't need to fret too much about our recent frosts. You may not get much of say, an apple crop, but most trees, shrubs, and flowers will be fine.

   There are exceptions. Domoto said he has a deciduous azalea at his Ames home that he covered with a sheet Wednesday night--but the developing flower buds were still toast (so to speak!).  

 

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How To Fight Frost 

 

Most of us know that you can prevent frost damage by throwing a sheet or other protective covering over your plants. (One fruit tree in my neighborhood sported four sheets, but that still didn't cover it all.)

   Domoto shared a great tip about an additional method to use: The night before a predicted frost, water the soil well around endangered plants. The increased soil moisture will help retained heat in the ground move upward during the night, perhaps making enough of a difference to protect your plant. It's the same principle behind never using a wet hot pad to take a pan out of the oven. The water assists heat transfer and can burn your hand.

Become a Frost Geek 

 

If you're like me, you like to know the "how" and "why" behind these things. So to become a frost expert in five minutes or less, read on!

   Key things to know about garden frosts:

  

     Light frosts vs. hard frosts. Light frosts are when the temperatures drop below freezing (32.8 degrees) but stay above 28 degrees, and typically only for a few hours. Hard frosts are when temperatures dip below that-and the colder they get and the longer they last, the more damage they do. (A "killing frost" is a loosey-goosey term that is usually used with fall frosts-it's a deep, extended frost that kills almost all annuals and the tops of most herbacious plants, such as peonies or daylilies.)

     How much damage a spring frost does to a plant depends on the cold-tolerance of the plant and how far along it is. Tulips and daffodils laughed at these frosts-they can tolerate cold. But fruit trees, which are a vulnerable stage of flower and fruit development because of all this weird, warm weather, experienced a lot of damage. It is not a good year to be an orchard owner. Many grapevines, said Domoto, were just starting to grow and were nipped to the ground by frost. However, they should regrow nicely.

     The amount of moisture in the air matters. The past couple of days, the humidity has been low (more specifically, the dew point) and that contributes to frost damage to plants.

     The amount of air movement matters. It's hard for frost to settle on plants when it's breezy. Wednesday night was fairly still, unfortunately.

     The lay of the land matters. If you're in a low-lying spot or valley, cold air can sink down and settle on your garden. However, if you're on a slope, the coldest air my well roll right on by. So you may have frost damage, but your neighbor down the road may not.

     Being in town or out in the country matters.In town, things like radiant heat from streets and driveways can minimize frost damage. But the lack of wind can encourage frost damage

 

 
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Garden To-Do List

 

  Set any seedlings you have started outdoors or garden plants you have purchased for several hours at a time to gather strength. If temperatures are not predicted to dip below 40 or 45, you can even leave them outside overnight.  

     

  Start weeding! This warm weather is giving weeds a head start.

 

 Divide perennials that bloom in the late spring, summer, or fall now, as needed or desired. (Spring-blooming perennials should be divided after they're done blooming through summer into fall.) 

  

 Prune most large trees, small trees, shrubs, evergreens, and roses now as desired. Wait to prune spring-flowering shrubs until after they're done blooming so you don't reduce the show

  

 If your lilacs, roses, and other plants get powdery mildew, now--before it shows up--is the only time to control it. Spray with a fungicide three or more times before temperatures regularly hit the 80s. 

  

 Plant nearly any type of tree or shrub now. 

  

 Plant cool-weather loving seeds, such as radishes, carrots, lettuces, spinach, peas, turnips, beets, and various greens now. It will soon be too hot!

     

 Plant seedlings of cool-season vegetables, such as broccoli, cauliflower, Brussels sprouts, and cabbages now. 

  

 Plant bareroot roses now. It's also now warm enough to plant roses growing in containers. 

  

 Plant herbs now that like cool weather, including parsley, chives, and cilantro. Also plant any perennial herbs.

 

Time to start feeding and mowing that lawn!   

Click here for details on what to do when.  

 

 Wait to plant warm-season annuals, such as marigolds, tomatoes, and impatiens, until after the last average frost date in mid-May.   

     

Other Timely Links

   

What To Plant When In Iowa 

 

20 Must-Have Perenials In Iowa  

 

Plant-Buying Tips for Iowa 

 

Deer-Resistant Trees and Shrubs for Iowa   

 

Pruning Basics

 

5 Simple Steps for Healthier Tomatoes

 

 Great Garden Event!
 
Spring Fever Symposium
Saturday, April 14
Iowa Arboretum
10 a.m. to 3 p.m. Roy Klehm from the renown Klehm's Song Sparrow Nursery. Learn about hardy magnolias and peonies. $45 for members and $55 for non-members Click here for more information and to register on-line.

Click here to see more upcoming Iowa garden events.

Click here to let us know about your garden event!

 

Garden Quote:  

"Bread feeds the body, indeed, but flowers feed also the soul."    

--  The Koran