Watering Before a Freeze

Posted by Annie Napier on 11/27/2017

You read it right! When a healthy plant receives just enough water, in the right places, in the right timing, the benefits outweigh the risks and good horticulture can protect a plant from nature’s winter fury!


 

Why?

When water inside the plant tissue freezes, it expands and destroys the cell walls. 

The length of time we are below freezing and how far below freezing does matter. If the temperature is not much below freezing, the rate of heat transfer from your plants (and particularly from the earth around their roots) is low.  If there is a lot of water present, the high heat of fusion means that it will take a long time to actually freeze much of it.  If it doesn't warm up much the next day the second night is more likely to kill them because the water in the soil is closer to freezing.  Generally, the longer the amount of time the temperature is below freezing, the worse the damage will be.

  • Water is an insulator, among other things. 
  • The hydrogen bonding that causes water to solidify releases heat energy into its surroundings as they are formed.
  • a wet soil loses heat much slower than dry ground/ holds heat better than dry soil, protecting roots and warming air near the soil.

Where?

  • Insulating plant roots and cell walls
  • Soil’s ability to retain heat from the sun
  • Humid air retains heat better than dry air

When?

During plant establishment and active growth:

  1. Do not over water your plants; over saturated soils produce shallower, less productive and generally weaker root systems that are more susceptible to frost damage.  Be especially careful not to over water plants in soil with poor drainage.
  2. Moist soil will stay warmer than dry soil, so a regular watering schedule in dry, cold weather can help protect plants from freezing temperatures

In preparing your plants for a freeze, do one or more of these things:

  1. Water the soil thoroughly (except around succulents). A thorough soil soaking early in the day before a freezing night allows the plant enough time to absorb the moisture. When you moisten the soil, two things happen. Some of that water will evaporate into the air overnight and moisten the air just above the ground. When the temperature cools, that moisture will condense into dew and that process releases heat into the air. This might buy you a degree or two.
  2. Promote even soil moisture with tree gators or donuts, the store of water also acts as an insulator against the cold.
  3. Water around the plant's base, again, before nightfall while the temperature is still above 40 degrees Fahrenheit, so that the soil stays moist throughout the freezing night.
  4. Irrigate with overhead sprinklers and keep it on overnight until after the sun comes up and begins to warm the air and ground.Stop irrigating when the ice is melting and temperatures are above freezing and rising. Ice breaking free from branches indicates water is forming under the ice and it is likely safe to quit. Normally this is when temperatures are above freezing and rising. Beware of sudden dips in the temperature soon after sunrise.
  5. Cover the plants to reduce heat loss- Bed sheets, drop cloths, blankets, plastic sheets or whatever you have handy will make suitable covers for vulnerable plants. Heat radiating up from the soil gets trapped under cover, and you can raise the micro-climate around that plant by 2 to 4 degrees F.  Use stakes to keep material, especially plastic, from touching foliage. Remove the coverings when temperatures rise the next day. For a short cold period, low plantings can be covered with mulch, such as straw or leaf mold.
  6. Mulch the soil to prevent water loss and add insulation
  7. Tactical measures: If there is too much out there to save, then hit the coldest spots in the yard:
  • Any low spot: Cold air is dense and will settle into low spots
  • Open areas: Plants under the shade of trees will have a little better soil moisture and air humidity, compared to those exposed to wintery winds. Protect exposed plants first.
  • New trees: Fill those gator bags!
  • Keep tender, potted plants above 40 degrees; even the garage or shade is a safe haven when you can "stack" mulch, water, heat sinks, and coverings to increase protection.

 Wishing you a successful over-wintering. 

 


 

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