Winterizing your Roses

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Ask three different rosarians how to winterize, and you'll get six different answers.

Some don't winterize at all.  Others go all the way - pruning back the roses to waist height, stripping off all the leaves, and burying the bottom of the plant with hauled-in mulch.  If you don't winterize at all, some years you'll lose a lot of roses.  If you go the whole nine yards, some years you'll still lose a lot of roses.  In mild winters those who don't winterize win, while those who do can lose roses to rot under all that warm wet mulch.  In cold winters those who don't winterize can lose everything, while those who do shouldn't lose more than top growth, but no guarantees either way.  Some (like me!) wait to see if it's going to get cold enough, and then end up winterizing in the dark after work as temperatures plummet, generally in sleet or snow. 

Why Winterize?

Modern, repeat-blooming roses are not hardy to extreme cold.  Garden roses are complex hybrids of numerous species from all over the Northern Hemisphere, and the repeat-blooming genes nearly all come from semi-tropical, evergreen species from China.  They can take frost, but not extreme cold.  My own experience is that most modern roses can take temperatures down to about 15º F (that's - 9º C) before sustaining freeze damage.

Species roses and once-blooming roses should not need winterizing, unless you're growing semi-tropical species in cold-winter areas.  Some modern repeat-blooming roses were hybridized specifically for cold tolerance:  Buck roses from Iowa, and Parkland and Explorer roses from Canada.  Most rugosa hybrids are pretty cold tolerant too.  All the European, once-blooming old garden roses are cold hardy:  the albas, damasks, gallicas, centifolias.

Other classes of roses are notorious for being tender here, like the Noisettes, semi-tropical roses hybridized in coastal South Carolina.  Tea roses have a reputation for tenderness that is not entirely warranted - it's lack of summer heat that gets them here, not winter cold.  Climbers and tree roses can suffer physical damage from snow load or high winds if not sufficiently supported, and the top of a tree rose is particularly vulnerable to freezing, being so far off the ground.

Frost and snow do not hurt roses.  What hurts roses is extreme cold, particularly when combined with a dry wind.  Wet snow and thick ice can cause breakage from its weight but snow is an insulator, it does not cause freeze damage.

When to Winterize?

While modern, repeat-blooming roses do not go dormant, they will harden off when exposed to cold temperatures.  This process prevents the water in the cells from freezing and bursting the cell walls - the cause of winter damage.  Winterizing too early prevents hardening off, and the roses will suffer winter damage despite the protection you gave them.  If possible, wait until the roses have experienced at least one good solid frost.  Some years that won't be possible, as we often get sustained mild temperatures in the 40s F and then a sudden plummet to the teens in just a couple of days.  It's best to watch the weather rather than insisting on a set schedule.  Some years the cold will come in October, but most years not til December or January, and some years not at all.

I have noticed, reading rose society newsletters from around the country, that in truly cold winter climates, people tend to winterize much later than we do!  For instance, the Greater Milwaukee (WI) Rose Society recommends waiting until there have been 'a few' hard frosts - this in their November newsletter!  And the Utah Rose Society recommends waiting until the ground is frozen, IF you're going to winterize at all(!).

How to Winterize?

First, plant your grafted roses with the graft union just below the soil surface.  Soil is the best insulator, and the graft union is the most critical part of a grafted plant.  If that graft union dies, then all you'll have is the rootstock sprouting up next spring.  Own-root roses do not have to be planted deep.  In mild winters this will be the only winterizing truly necessary.

Second, pile some kind of insulating material over and around the bottom of the plant.  If you like you can prune the top down a bit and strip off the leaves first, this does make the job easier, but is not necessary.  Ground bark, compost, mushroom compost, wood chips, leaves, and soil are all good materials.  Don't scrape up soil from around the roses though, as this just exposes the roots to cold and dry.  You'll probably hear a lot about how certain leaves should never be used as they rot or skew the pH - don't bother.  Use whatever leaves you have at hand, they're all good unless you've got walnut or eucalyptus, and those trees are rare here.  If you do use leaves use a lot as they will decompose and settle over the winter.  I like to add a cover of Douglas-fir branchlets over the cone of leaves to help hold them in place.

Prevailing winds are from the southwest, but the coldest, most damaging weather usually features northeast winds, so pay special attention to that side of your roses when mulching.  Make sure you have good cover over, under, and between all the canes for 6-8" from the soil surface.  Gaps will let in the cold.  You want to keep the extreme cold from getting to the base of the plant.  In cold winters, your rose canes will probably die back to the level of the protection so heap it high.

Tree roses are best protected with pipe insulating foam on the trunk, soil piled at the base, and the top graft wrapped in bubble wrap or some other nonabsorbent insulation.  Make sure the whole thing is securely staked, too.  Some people put christmas lights on their wrapped-up tree roses for decoration.

Climbers just plain have to be cane-hardy here, and most are, with the exception of the Noisettes and Hybrid Giganteas.  You should insulate the base of the plant just like any other rose, and then make sure the canes are tied up securely.  Then hope for the best.  Usually that's enough and you don't lose much top growth.

Potted roses need the root area protected as well as the top.  Sink the pot into the ground, the compost pile, or a plastic crate filled with wood shavings or leaves.  Many people like to move potted roses into shelter for the winter but you have to have an unheated, lighted shelter - unheated garage or shed with windows, or an unheated hoophouse or greenhouse.  Don't bring them into the heated house, that's too warm and dry and dark for them.  They'll try to continue to grow but the inside of your house is too dark and dry for healthy rose growth.  If you use extruded-foam insulated pots then you don't have to worry about the roots, just leave them in place.

When to remove it all?

March, usually.  When the forsythia bloom.  Be gentle so you don't break off new growth.

Here's Aloha, wearing her leaves and Doug-fir skirt for winter:

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