JARS v51n2 - The Rhododendron Standard

The Rhododendron Standard
Impressive and Easy to Create
Clarence 'Slim' Barrett
Eugene, Oregon

You seldom see standards anymore. I have several in my garden and they always draw more attention than most any other feature. They are easy to create but do require patience. It takes a number of years for them to become really decorative.

A standard, of course, is a dwarf or semi-dwarf rhododendron grafted on a very tall, single stemmed rootstock. Rhododendron 'Anna Rose Whitney' is an excellent candidate for the rootstock, but any robust grower will do. 'Anna Rose Whitney' tends to have 8-inch to 12-inch flushes of growth, and since the rootstocks should be at least 4 or 5 feet in length you are looking at several years' time just growing them. I raised them in a bed and planted them about 16 inches apart each way so that as they got tall they were inclined to support each other. Preferably the planting bed should be in at least filtered shade, and full shade is okay. This tends to promote longer flushes of growth and provides protection from direct sun when the grafts are eventually made, which can be done without moving the rootstocks from the original bed.

Remove all side branches as soon as they start to develop so that all the plant's vitality goes into the center stem. When the rootstocks have reached their desired height, and just as their spring flush of growth begins to harden, cut off the stem just below the bottom new leaf, leaving last season's leaves in place. With a sharp knife, split the stem down the middle about an inch or so (Fig. 1). Scions about 2 to 3 inches in length will have been gathered just before cutting the rootstock and all but the top three leaves removed. Cut the base of the scion's stem into a wedge shape about an inch long and insert this wedge snugly into the split on top of the rootstock (Fig. 2), being careful to align the cambium layer on one side of the scion with the cambium layer on one side of the rootstock. Since the scion will probably have a much smaller diameter than the rootstock I usually insert two scions, one on each side of the rootstock.

Now very carefully, and rather tightly, wrap the union with a rubber grafting strip about 6 inches long, being careful to tie the final end so it stays in place when released. A ¼-inch by ¾-inch rubber band may be cut and used as a grafting strip. Check to be certain this process did not move the scions out of alignment. Now place a plastic sandwich bag over the entire graft and fasten the bottom end closed around the stem with a "twistee" just below the union. Be sure the graft is shaded since direct sunlight on the plastic bag will cause heat to build up and quickly kill the scion. After two to three months the scion will begin to grow and the plastic bag can be loosened a bit to let a little air in. If the scion wilts fasten the bottom of the bag closed again. If it does not, your graft has succeeded, and after another couple of weeks you can remove the plastic bag entirely.

For me the grafts were more successful if the scion was more mature than the rootstock. That way it made fewer demands on the rootstock for moisture and nutrients until the union had a chance to heal. As the scion completely heals and puts on considerable growth it is time to remove the old leaves from the rootstock.

A traditional favorite subject for standards has been R. williamsianum , and its effect is indeed spectacular, presenting a pink snowball about 5 feet above the ground. I have a number of forms of R. yakushimanum as standards, and they never fail to draw admiration, partly because of their compact growth habit and faultlessly mounded profile. Other good candidates are 'Lori Eichelser', 'Scarlet Wonder', R. roxieanum var. roxieanum Oreonastes Group, and 'Creeping Jenny', which has a weeping effect. These are some that have worked for me, but I am sure there are many others. I once thought R. makinoi would be a good subject, but unfortunately all my efforts in that direction failed, for what reason I do not know. Lepidotes, of course, normally will not graft to elepidotes because of incompatibility.

As the accompanying photographs indicate, I like to support standards with a length of ½-inch steel rebar, with 3 feet driven into the ground next to the main stem of the rootstock and 4 feet or so above ground. We have quite a lot of wind on our hill, and as the top of the standard gets larger it catches more wind and is apt to be broken or blown over. These rootstocks were grown about five years before grafting and the grafts were made about eight years ago.

Slim Barrett, a member of the Eugene Chapter, is author of the book History of the Rhododendron Species Foundation, Genesis of a Botanical Garden.