Cold Climate Gardeners: Stick to Own-Root Roses

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20170926A Felix Leclerc netpsplantfinder.com

Rosa ‘Félix Leclerc’ is almost always grown on its own roots. Photo: netpsplantfinder.com

In just about any garden center, you’ll find roses produced two different ways.

Some were produced by grafting: a rose with the desirable characteristics was grafted onto a rose of lesser ornamental value and thus grows on the root system of a different plant.

Others were produced by cuttings, sometimes even by tissue culture: they grow on their own roots.

If you garden in a region with rather mild winters (zone 7 and higher), that doesn’t really change the situation much: both multiplication methods are legitimate. But if you garden in a colder region (zone 6 and below), that’s a different story, because grafted roses are much less hardy than own-root roses.

The Glory Days of Grafted Roses

There was a time not that long ago where most roses were grafted ones. Hybrid teas, grandifloras and floribundas, all fairly tender plants, were the norm, but that’s changing.

20170926D Olivia Rose Austin davidaustinroses.com.jpg

Rosa Olivia Rose Austin, one of the David Austin roses, is now available both grafted and own-root. Make sure you choose the right one for your climate! Photo: davidaustinroses.com

Own-root roses now dominate the market in many areas. The popular Canadian series of extra-hardy shrub roses, for example, including the Explorer, Parkland, Canadian Artists and new 49th Parallel series, are almost always sold growing on their own roots. And more and more European and American roses, especially shrub roses, also grown that way, including many in popular series like David Austin roses, Meilland roses and Kordes roses.

Why Choose Own-Root Roses?

But why are own-root rose bushes hardier than grafted roses? The answer lies partly in the rootstock chosen.

The rootstock is the plant onto which a graft is spliced. In the case of roses, which belong to the botanical genus Rosa, the rootstock must necessarily be another rose. You can’t graft a rose onto a cedar or apple rootstock. The result is that the rootstock provides the roots, while the graft gives the resulting plant its overall appearance and habit plus, of course, its flowers. Theoretically you never see the rootstock: it grows underground, sight unseen, but it still does its job of providing water and minerals to the plant above.

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Rosa ‘Dr. Huey’ is a rambling rose with small red flowers and a rangy habit. Its leaves are generally considerably smaller than the bush rose it tends to replace. Photo: gardenweb.com

The majority of grafted roses these days use as a rootstock a small rambling rose called ‘Dr. Huey’. Rose growers like it because it’s easy and fast to multiply from cuttings and gives good vigor to the roses grafted onto it. Other roses used for grafting include R. multiflora and R. ‘Fortuniana’, all rather insignificant bloomers if grown on their own, but that readily accept grafts from other roses.

The Problem With Grafted Roses

The initial problem for cold-climate gardeners is that most rose rootstocks are not very hardy. R. ‘Dr. Huey’ will grow in zone 6, but is only borderline hardy there and often dies back severely in winter. It really only performs fully in zones 7 to 9, zones clearly insufficient for cold climate gardeners. R. ‘Fortuniana’ is even less hardy. Plants grafted onto these often simply die over the winter. With the rootstock dead and therefore no roots to nourish the upper growth, the rose above therefore dies as well.

R. multiflora is a hardier rootstock, surviving, although barely, in zone 4, but thriving in zone 6. However, it’s a weedy plant given to producing invasive suckers and has thus largely fallen out of favor as a rootstock.

But the rootstock, being planted deep underground, often survives in spite of its limited hardiness, and that causes an entirely different problem. Now it’s the upper part, the grafted rose, often a hybrid tea, grandiflora or floribunda, that dies. (All three are normally only hardy to zone 7 or 8, although they’ll live in zone 5 if covered with a rose cone for the winter.) What then happens is that, with the grafted part dead, but the rootstock still alive, the latter sends up its own shoots, producing a very different rose. Confused gardeners are then left wondering how that hybrid tea with is thick stems and big double orange flowers is now producing a scrawny, small-flowered, creeping rose.

If, however, you planted an own-root (non grafted) rose and the upper part dies during the winter for whatever reason, there is a good chance that it too will regrow from its roots. The difference is that the rose that grows back will be the original ornamental variety, the one you chose. That’s a huge improvement!

Another problem is that most rootstock roses, which have been grown from cuttings for generations, have picked up plant diseases, notably rose mosaic virus (RMV), and these diseases are carried to the ornamental rose when it’s grafted onto the diseased rootstock. RMV often shows few specific symptoms, but rather gives a weaker growing, poorer flowering plant. Not exactly what you want.

Gardeners Push for Better Roses

A lot of the trend toward own-root roses is due to pressure from home gardeners. Those in the know are leery of grafted roses and request own-root types. Salespeople have noticed the change and therefore bring in more own-root plants.

Still, there’s more profit to be made from grafted roses that die after a few years and have to be replaced than from long-lived own-root roses. So, as long as there are still hordes of beginning rose growers who don’t know the difference, most garden centers will keep on selling grafted roses, in spite of disappointing results. But word has reached even novice gardeners that roses are “difficult plants” and sales of rose bushes have been declining as a result. Yet roses are not necessarily difficult to grow, at least, not if you buy own-root roses.

How to Recognize an Own-Root Rose

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A grafted rose will have only one stem with a swollen bud union at its base. Illus.: stalbertbotanicpark.com

Recognizing a grafted rose at purchase time is easy enough. At the base of its single stem, there is a swelling: the graft union, the point at which the graft was originally made. An own-root rose won’t have this swelling: the stem will be of the same thickness from the roots to at least half its height. In addition, there are usually several stems rising from underground on own-root roses rather than a single stem.

If in doubt, ask the salesperson to help you pick out a rose bush growing on its own roots. After all, you don’t want to plant a grafted rose, at least not if you garden in a cold climate.

When to Plant Roses

You can plant hardy roses almost any time of the year as long as the ground isn’t frozen, from April/May to October/November, depending on the local climate. However, garden centers often sell roses are at a better price in the fall than in the spring or summer.

Just plant own-root roses as you would any perennial or shrub, at the same depth as it was in the pot, and apply a good mulch. In mild climates, you would also plant grafted roses at the same depth as it was in its pot, but in cold ones, the graft union should be planted so it is covered with 1 to 2 inches of soil to help protect it from the cold.

That said, cold climate gardeners would still do best to avoid grafted roses entirely and to stick to the hardier own-root types. Why make life complicated when it can be so simple?20170926A Felix Leclerc netpsplantfinder.com

 

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2 thoughts on “Cold Climate Gardeners: Stick to Own-Root Roses

  1. Iman Nosseir

    Hi Larry. Do you have recommendations for an own-root rose that would be good for a street front hedge on a Montreal street. I’m concerned about salt etc.

    Thanks so much for sharing your treasure trove of information with us novice gardeners.

    • Look into any of the Rosa rugosa hybrids. They’re all very salt-resistant and in fact, the species grows abundantly all along the Gaspé coast where it gets a lot of salt spray. Excellent hardiness too! Hybrids include ‘Hansa’, ‘F J Grootendurst’, ‘Jens Monk’, ‘Blanc Double de Coubert’, ‘Henry Hudson’, ‘Pink Grootendurst’ and the entire Pavement series. This is an excellent question and I’ll probably write up a longer list for a blog in a few days!

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