Rose cell walls contain water and it is the major component of plant tissue.
When water freezes and expands at temperatures below 32 degrees, ice crystal
formation develops in the living tissue and causes the cells to rupture. Damage
occurs which can also result in death of the plant.
USDA Hardiness Zone – the lowest temperature a rose can withstand without
injury. (Memphis – > category 7b {10 – 5 degrees F}) Without
protection, modern roses (HT, FL, climbers) are often damaged by temperatures
of 10 degrees F or colder.
Plant cell walls thicken as they prepare for dormancy. This process is often
called "hardening off" and occurs when the temperatures gradually
decrease. The canes often give off a purple cast when allowed to properly harden.
If there is not a gradual decline in freezing temperatures, the roses are more
susceptible to damage when exposed to subfreezing levels.
Winter protection is added to give the bush a better chance to initiate its
own natural freezing mechanisms and to maintain a fairly constant temperature
which will provide insulation from the cold temperatures thereby avoiding the
"freeze – thaw" seesaw.
(During the month of October, you should…..)
Maintain your spray program. Use a fungicide to prevent black spot, etc. Sickly
/ diseased bushes in autumn may not survive the winter (with or without protection).
After roses go dormant, several times through out the winter, use a dormant/horticultural
oil, or lime-sulfur spray to kill fungal spores and eggs from garden pests that
could winter over.
Do not deadhead. Allow the roses to "go to seed" or "set hips"
by only pulling the petals off. Pruning will encourage sap to rise to form new
tender growth, which will freeze when temperatures drop and cause damage to
the plant.
Rid the bed of dead and fallen leaves prior to adding winter protection. Old
leaves harbor spores of fungal diseases and the next generation of garden pests.
Check the pH of soil. Add lime now to allow for time to correct to pH of 6.3
– 6.8 in spring. Add at a rate of 1 cup to large bush (1/2 cup per mini)
if below 6.5.
Scratch the lime into the soil taking care not to damage roots.
Add 0-20-20 (fertilizer that contains no nitrogen). 1 cup per large bush (1/2
cup per mini). Scratch the fertilizer into the soil around the dripline taking
care not to damage roots.
After the SECOND OR PERHAPS THIRD hard freeze (temperatures below 28 degrees
F), roses will go into dormancy. Locally, this usually occurs near the end of
November. THEN YOU SHOULD:
Wind prune hybrid teas, grandifloras, and floribunda bushes to the height
of your waist. This prevents the bush from rocking in the strong winds. Minis
should be pruned to knee-high height.
Protect the canes from drying out by using an anti-desiccant spray. Wilt Pruf
and Cloud Cover are two name brands that are used prior to adding the winter
protection. The canes have a tendency to dry out due to high winds / low humidity
since the roots of the rose bush are now dormant and unable to supply the canes
with more moisture.
Cut or chopped leaves, pine needles, mulch, soil, sand, manure, and coarse sawdust
are examples of materials used for winter protection. Organic materials break
down over the winter and feed the bush in the spring. In this area, all hybrid
teas, grandifloras, and floribundas need a minimum of 10-12 inches of winter
protection material mounded on the base of the bush. To hold the materials in
place, numerous devices can be used: Styrofoam formed into boxes held by duct
tape, shingles held with twine, commercial collars, burlap, chicken wire, or
several layers of newspaper folded lengthwise and stapled. These devices assist
when mounding with loose filling material. Choose a material that drains well
to prevent a soggy mess that can cause cane die back.
Some roses need extra protection. Known "winter tender" varieties,
bushes grafted on rootstock (ex. Fortuniana), and typically bushes that are
the color yellow tend to be more susceptible to harsh temperatures. After hilling
or mounding the winter protection around the base of the plant, trim the canes
to allow the bush to fit under a bushel basket or large plastic garbage can.
You may also construct your own Styrofoam box to cover and enclose the bush.
Rose cones are available from garden supply companies and must be weighted down
with several bricks to endure the high winds. The cones or boxes must have adequate
ventilation. NOTICE: WHEN COMPLETELY ENCLOSING A BUSH, ALL FOILAGE MUST BE REMOVED
TO PREVENT FUNGAL INFECTION / ROTTING.
The key to prevent winter damage is to keep the bushes dormant. "Own root"
bushes and mini’s are hardier. There is no bud union to protect and if
conditions are severe and the bush dies back to the ground, chances are that
your bush may still survive since it is on its own roots. Miniatures can be
covered with several inches of leaves for protection. Some rosarians prefer
no winter protection for their minis, but I’m not that brave. My favorite
minis that I can’t live without get a mounding of winter protection.
There are several methods for winterizing roses grown in pots. You may dig holes and sink the pots, move the pots into a "cold frame", leave huge pots in place and heap pine needles around them, or huddle the pots together and form a barrier shield of filled lawn bags around the perimeter. Remember that potted roses still need water and will retain it better if placed on soil rather than stones, concrete, or bricks. Tree Roses should be dug up and stored in a cool garage or basement.
There are several methods for winterizing roses grown in pots. You may dig holes and sink the pots, move the pots into a "cold frame", leave huge pots in place and heap pine needles around them, or huddle the pots together and form a barrier shield of filled lawn bags around the perimeter. Remember that potted roses still need water and will retain it better if placed on soil rather than stones, concrete, or bricks. Tree Roses should be dug up and stored in a cool garage or basement.