Freeze Stages of Trees & Shrubs

Freezing of Soil

• At temperatures between 23 and 32 F, soil water can freeze, but woody plants may easily survive until temperatures become much colder. Cold-tolerant trees may be able to protect plant cells themselves from freezing through the use of intracellular transport. Water usually freezes just below 32 F because of particles in the water that reduce the freezing point. Ice crystals may form on the surface of the soil. Tree and shrub roots may be under pressure, but can generally sustain such stresses.

Freezing Between Plant Cells

• Certain plants, such as pine trees and many other evergreens, are able to sustain frost by expelling water into the spaces between their cells, so that the cells themselves do not freeze, called intracellular transport. This occurs at temperatures between 14 and 23 F. Needles and leaves may seem stiff and brittle during this stage. They may seem frozen, but in fact the living cells are still alive and have not yet frozen.

Freezing of Roots and Plant Cells

• At temperatures between -4 and -40 F or when the temperature drops rapidly, many plants may succumb to freezing. These frigid temperatures cause plant cells to freeze and die. Branches may die off when this occurs. Plants are especially susceptible when they are dehydrated. Root death is another factor of freezing plants and varies among tree and shrub species. Magnolia stellata roots die at 23 F, while eastern white cedars can survive much more frigid temperatures.

Frost Damage Protection

• A number of mechanical approaches to cold protection can help trees and shrubs survive low temperatures. Apply mulch to reduce root freezing and maintain a stable temperature, particularly if plants are shallow-rooted. Use bark, peat moss or straw. Another helpful method is to tie up branching plants, such as juniper and yew, to support the branches from falling due to weight of ice. Apply anti-transpirant to reduce loss of moisture, which can dessicate plants when they are unable to absorb frozen water.