Week 40: Merry Frostmas And How to Save Dahlias From Frost

How to save dahlias from frost

Monday (October 3rd), we had our first killing frost of the season, which I affectionately refer to as “Frostmas.” Most years, I feel a major relief when Frostmas comes, knowing the season is coming to a close, and I can look forward to the slower pace of winter. 

This season, it was both a relief and a disappointment.  The frost came quite early this season, and we still have one week left of our fall CSA, which means I still need LOTS of flowers (Yikes!).  At the same time, I felt happy knowing I could finally mow down my mildew-ridden zinnias that I was tired of looking at.

Luckily, I had a few tricks up my sleeve so I could have the best of both worlds.  I managed to save most of the dahlias, while saying goodbye to tender annuals such as zinnias, ageratum, and cockscomb celosia (we mowed those suckers down the same morning of the frost!).

There are a few different ways you can protect your flowers from a light frost:

A)    Cover them with frost cloth (lots of material, labor, and effort)

B)    Use a wind machine or helicopter (expensive!)

C)    Water the crap out of them (fairly easy and inexpensive)

I choose option C. 

I protect flowers from frost by thoroughly overhead watering them.  There are a few specific theories that explain why this works, but basically, since water is warmer than 32 degrees (freezing temperatures), it insulates the plants just enough to protect them from a light frost.  

When I learned there was a possible frost forecasted, I prioritized saving the dahlias specifically for our CSA members, since it’s impossible for me to save all the field annuals, and they are the most popular and profitable crop at this point in the season.

I stayed up late Sunday night hand watering and setting up a sprinkler system to heavily overhead water most of our dahlia field.  Then, I got up at 4am on Monday morning with my trusty headlamp, and walked up and down each dahlia aisle, overhead hand watering each dahlia plant with a hose and wand attachment.  I also used an overhead sprinkler system to aid in adding moisture and warmth into the dahlia patch.  I walked the aisles and repeatedly watered each plant until well after sunrise.  

I luckily managed to save most of the dahlias!  Our CSA members will be very happy to have flowers for their last scheduled CSA week. 

Every season when I deploy this tactic I am shocked that it actually works!  I am so thankful to know and use this money saving technique. 

It’s great because now we can fulfill our CSA obligations, and continue sales for at least a few more weeks- resulting in a lot more revenue for the season.

It’s actually insane that our revenue is highly dependent on something as out of our control as the first frost, but this is farming, and all we can do is try our best to mitigate risk as much as possible.

I highly recommend the watering method to save your plants from frost to extend your season for a few extra weeks. 

Here are some tips you’ll find useful in protecting your plants from an early, light frost:

IMPORTANT NOTES ABOUT FROST & PROTECTING YOUR PLANTS

WATER EARLY AND OFTEN

It's important to start watering very early morning (in the dark) before the sun rises.

The temperature is usually coldest just before or just after sunrise, which is when the temps can dip below 32F and frost forms (This is especially true when the weather is clear and calm).  You want your plants to be doused with moisture well before the temperatures dip.

I am certainly no meteorologist, but from what I understand, this is because at night, when there is no sun, the earth stops receiving solar radiation, yet the earth continues to radiate heat from the surface.  This results in a drop in temperatures (known as radiational cooling).  As the sun peaks up in the morning, its radiation is very weak and often is not enough to counter the cooling of the earth yet.  It is not until the sun gets higher in the sky that the solar radiation is stronger than the the exiting radiation, and the temperature begins to rise.

There is also another theory that says because of radiational cooling, on clear nights the ground gets much colder than the air just a few feet above it. Then, once the sun comes up, the sunlight excites the cold air in the first foot or so above the ground (which can be 10 or more degrees colder), which causes it to move around and mix into the next several feet of air. That “mixing upward” drops the temperature of the air right around sunrise.

Because of this, I always put my temperature probe right at the grounds surface, to ensure an accurate reading.

 KNOW YOUR MICROCLIMATE

Our farm is located in a small valley, and our flower field is specifically set on the lowest part of the farm, with two hills on either side of the field (not ideal).  Because of this, our flower fields are generally much colder than the surrounding area because cold air is “heavier” than warm air and settles in low spots.  I know the flower fields are colder from paying close attention to forecasted temperatures and comparing them to the actual temperature in our fields.  Whenever temps are forecasted to dip into the high 30’s, I know from experience that it’s a possibility we may get a frost – even if other farms right down the street won’t.

ACCURACY IS IMPORTANT

Be sure to monitor the temperatures RIGHT in your fields.  You can’t rely on weather apps or general weather stations in your town to tell you the temperature in your flower fields.  Be sure to use your own thermometers and weather stations in your growing areas.  I use simple remote thermometers that I can read the field temps right from our living room, so it’s easy to monitor.  A great example of this is that our house is nestled into a hill, well-protected by trees in the woods just uphill from the flower fields, and is often an entire 10 degrees warmer than the flower fields!  That is a huge difference!

 CONDITIONS MATTER

If temps dip into the mid-high 30’s, I ALWAYS consider a possibility of frost depending on other weather conditions due to the location of our flower fields.  Cloudy, rainy nights have a much less of a possibility to frost than clear nights.  Cloud cover and wind provides some protection, and holds warmth from the earth so there is less chance of a frost.  Pay attention to other weather conditions besides forecasted temps alone to assess the risk of frost.

 BE READY FOR SURPRISES

We have been surprised by completely un-forecasted frosts before.  As we all know, the weather can be unpredictable.  Come autumn, make sure you have planned intelligently so you don’t put yourself in a pickle.  For example, don’t schedule your CSA pick ups during peak frost threat season – or else you may have lots of unhappy customers!   Everyone’s risk tolerance is different, find what you are most comfortable with.

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All in all, I am ready to begin fall clean up but am thankful for another few weeks of flower sales and revenue.  I wouldn’t have this type of control without these flower-saving techniques in my back pocket, and I hope sharing them has helped you in some small way.  Best of luck with the remainder of your growing season, and “Merry Frostmas” from our NY (zone 6) farm to yours!

PS- Did you find this useful or helpful?  Please let me know in the comments below!