War of roses: rootstock vs. scion


Crystal asked me what's wrong with the roses at her new home. It's a wonderful old place with extensive gardens where two plants have her baffled. The roses aren't blooming, she says, and they don't make hips, either. She wondered if perhaps they had grown too old to bloom, and should she replace them.

This is a great example of a fact of grafted roses. When a new variety is developed, the growers use grafting or budding to get as many new plants from that original variety as possible. It's a far more efficient way to exploit a limited amount of varietal cuttings.

Growers begin a cheap species rose that maintains all the vigor and disease resistance of a wild plant. They root cuttings by the thousands. These become the rootstock upon which the new variety, known as the scion, will be grafted. Each graft must be meticulously hand-spliced in the wholesale grower's nursery. Newly grafted plants go into the field supported with wax and rubber to hold the union tightly in place. In a few months, both pieces fuse into one plant.

Most roses you buy today are grown by this process. One of the most common rootstock species is Rosa multiflora, a wild rose that has all the bramblelike habits of its cousins except it lacks thorns. Multiflora is smooth-stemmed, which makes it easier and less painful for grafters to work with. Also, grafters know instantly what bit of rose on their bench is multiflora and what is the new thorny variety.

Out in the garden, the grafted rose is two plants that become one, but the scion may not be quite as vigorous as the multiflora rootstock. This is the Achilles' heel of all grafted plants. If it is subjected to severe stress from heat, cold, drought, pests or disease, the scion wood suffers most. In fact, it's not uncommon for the scion to die altogether, leaving the rootstock alive to grow freely.

Under normal conditions, the grafted rose will bear the habit, leaf and flower of the scion variety. Normally a rootstock produces no growth per se, but if it is injured by a misguided rake or pruning saw, it may produce suckers. This undesirable growth literally "sucks" energy away from the scion wood. Suckers will bear the leaves and flowers of the rootstock so you'll be able to discern it from the scion wood to cut it away. With multiflora rootstock, for example, it will lack thorns.

Crystal's roses were an example of rootstock die-off. They are along a fence line, which means they could have been eaten by animals or girdled by a string trimmer. This spelled the demise of the scion wood, but the rootstock survived to grow large and lush.

Once a rootstock runs wild like this, there's no regrafting the rose without special care and pruning. Plus, competent grafters are as scarce as hen's teeth. The best solution is to remove these rootstocks and replant with a new rose.

When removing the old rose, it's important to dig it out entirely because rootstocks can sprout from roots left behind for many years to come.

Crystal's story is one found across America where grafts have died off to allow rootstocks to run amok. It's the single most important reason for new interest in growing roses on their own roots rather than using grafted plants. This is particularly true for rural and suburban home sites where big beautiful roses aren't coddled and homeowners don't have time to prune fussy plants.

Before the commercial rose industry made grafted plants the norm, gardeners were growing roses from their own cuttings for many generations. Those brought west with the pioneers were rooted cuttings that came in peace before commercial growers began the modern war of rootstock vs. scion.

Maureen Gilmer is a horticulturist and host of "Weekend Gardening" on DIY Network. Contact her at her Web site www.moplants.com or visit www.diynetwork.com.

 

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