Grafting, Rootstocks and Hybrid Roses

By Maureen Gilmer
DIY--Do It Yourself Network

With more than 8,000 varieties, no wonder we get sensory overload when introduced to the world of roses. So how to get a handle on this popular plant when you're not a garden aficionado?

Start with understanding how roses are made. This factor among hybrid teas is one of the greatest sources of confusion among new rose fans. Simply put, it's all related to form and function.

Say Joe Smith, rose breeder extraordinaire, finds a cool seedling in the offspring of his favorite rose parent plants. These can be any two of the 8,000 mentioned above. The seedling blooms in a unique combination of red and yellow shades that has never been seen before. Smith scours the literature and gets so excited at finding the 8,001st variety that he names it after himself: Rosa 'Joe'.

Smith has to figure out how to get 'Joe' to market quickly and in quantities that will make him money. He only has the one 'Joe' plant, and chopping it up to make cuttings might yield just a few dozen plants. So Smith decides to make new plants by bud grafting, which takes only one bud sliced off 'Joe' to make a new plant quickly. That bud, or scion wood, is slipped under the skin of another common rose, known as the rootstock. It may be two or three years old. This produces a huge quantity of new shrub roses with the least amount sacrificed from the original 'Joe' seedling.

But Smith thinks people would prefer 'Joe' as a climber. So he chooses a different rootstock, one that is a strong climbing type. Rose grafters all over the world also use this rootstock because it's strong and reliable. He buds in 'Joe' and new plants grow into climbing roses that produce the 'Joe' flower.

If Smith wants to make 'Joe' rose trees, he chooses yet another well-known rootstock. This one is famous for making roses grow very upright with a strong trunk. The rootstocks have been grown in the field and trained to a single trunk before they are allowed to branch out. When Smith orders, they dig the plants out of the field while dormant and saw off the top growth. Smith's order arrives in nice straight trunks with roots. He grafts 'Joe' scions into the top and these grow into the 'Joe' rose tree.

The story of how 'Joe' changed forms explains why you can find a modern hybrid tea such as 'American Beauty' or 'Peace' in shrub, climber and tree forms. This causes confusion because novices think each form is a different variety. It's not. Just a difference in growth and grafting strategy changes form. Not all hybrid teas are grown in every form, however, which is simply a marketing decision by nurseries.

Knowing this, you can understand why it's a problem when rootstocks start growing their own branches. These "suckers" will look a lot different than 'Joe', often with changed leaf size, color or shape. When they bloom, it will be nothing like 'Joe'. The more these suckers grow, the less energy is funneled into the scion growth of 'Joe'. Therefore, it's essential you keep the rootstock completely free of its own stems and foliage so that 'Joe' gets the whole pie and looks great.

Sometimes grafted roses stressed from damage, poor care, disease or drought will react by letting go of their scion wood. This means that all the 'Joe' part will just die off. In its place rank growth from the rootstock will take over.

Understanding how roses are propagated through grafting is essential to really knowing these plants. Because if you're not paying attention, 'Joe' can die out over time. Come next year's bloom you might be very surprised to find only part of the plant is 'Joe'. And sometimes an entirely different plant has emerged from the rootstock after 'Joe's untimely and unexpected demise.

(Maureen Gilmer is a horticulturist and host of Weekend Gardener on DIY-Do It Yourself Network. E-mail her at mo@moplants.com. For more information, visit www.moplants.com or www.DIYnet.com. Distributed by Scripps Howard News Service.)