Across Missouri, grafting knives are being sharpened and scion storage refrigerators are being opened as nut growers head to their orchards to graft material taken from high quality trees earlier this year to rootstocks of run of the mill trees.
Grafting has been practiced for thousands of years although its actual origin is up for discussion. The first definitive written account is attributed to writings from Greece dated 324 BCE but the descriptions detail a number of practices that were apparently commonplace. Grafting not only allows you to faithfully replicate a high quality tree but is also used to combine characteristics of the rootstock, such as dwarfing and disease resistance, with the high quality fruit produced by the scion.
There are a number of different grafting techniques which can be used. All focus on matching the cambium, a thin layer of growing cells just below the bark, of the scion and rootstock. Grafts can be used on everything from very small saplings to large trees, where bridge grafts are employed to save damaged trees, for example, where beaver have effectively freshly girdled a tree, disrupting the flow of nutrients up and down the trunk, but the tree hasn’t been damaged to the point that it will drop. About the only caveat is that the scion and rootstock must be the same or closely related species.
Many grafting techniques are demonstrated on U-tube videos, but not all provide good results when used on nut trees. The publication” Propagating Pecan and Black Walnut (available to download at: http://extension.missouri.edu/explorepdf/agguides/agroforestry/af1003.pdf) is a good introduction to those specifically recommended for nut trees. Another, more general but also helpful, grafting reference is the MU Extension publication titled “Grafting” (https://extension2.missouri.edu/g6971). The side graft, in Figure #4, is simple and also effective and can be accomplished using a pair of bypass pruners and a utility knife. The trimmed scion is inserted into a cut made into the side of the rootstock that is opened by pushing on the portion of the stem above the opening. When that pressure is released, the stem springs back, holding the scion in place. Of course, you must wrap the junction with grafting tape to reduce moisture loss from the cut edges. By cutting the rootstock about four buds above graft, you build in a bird perch without attaching a separate stick. Little details: the FLAT slope cut on each side of the scion should leave equal amounts of material on both edges, otherwise only one exposed cambium will contact the cambium of the rootstock. If the scion isn’t large enough to entirely bridge the width of the cut, all is not lost. You can trim another stick or simply match one side as this is often successful.
Followup care of the graft consists of monitoring rootstock buds above the graft and rubbing them off at the first sign of greening: if you don’t check carefully, that vegetation may lead you to think your graft has been successful when it has failed. Once the graft has begun to green, attach a second, taller stick to the rootstock to keep birds from landing on the tender sprouts.
The grafting techniques discussed here are best done in the spring, when the nut trees are breaking dormancy and before temperatures become excessive as grafts often fail once temperatures get above 90 degrees. Not all grafts will be successful but making certain that the scion material has been stored properly and is still dormant, careful alignment of the cambial layers of the scion and rootstock, and protecting the graft union from desiccation will greatly improve the likelihood of success. While the text and pictures referenced here will be helpful, nothing beats seeing the process in action and hearing the tips of an experienced grafter. The Missouri Nut Growers Association offers such an experience at its annual grafting and scion exchange meeting. Unfortunately, due to COVID-19 it was necessary to cancel the event this year. The 2021 event should take place in late April or early May, so revisit out home page after April 15, 2021, for an update.
As we prepare the Spring newsletter there are many concerns about the spread of the Corona virus. President Mike Lucas, in consultation with board members, has decided to cancel our May meeting. We are fortunate in having two medical professionals associated with the board and they concur that, given what we know at this moment and respecting current directives from local governments, that this action is appropriate.
You are urged to follow any updated CDC guidelines (visit https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/summary.html#anchor_1580064337377) and common sense. Wash your hands!
Scion exchange update...In light of the spring grafting meeting being canceled, I'll be facilitating an informal scion exchange. Several folks have offered up scion and there have been several request for scion - all of which is GREAT! The the following scion is available. Pecan - Kanza, Pawnee, Gardner, Shepherd, Yates 68, Lakota, Major, Meramec, Harc, Chetopa and Manson 1.
Black Walnut - Kwik Krop, Football, Hay, Emma Kay, Neel and Tom Boy
And some English Walnut.
Please feel free to contact me. I can be reached at 816-293-5819 (leave a message) or via email email@example.com.
I plan to do/coordinate the shipping the week of April 13.
Thanks, Mike Lucas
April showers bring May flowers…it’s a well known phrase but those who have an eye for detail, or a reason to look, know that trees have been blooming for several months. Bee keepers watch for willow, maple, and elm blossoms that may appear as early as February and serve as an early nectar and pollen source for their hives when the bees venture out on warm days.
For nut growers, dangling hazelnut catkins in early March are sometimes the best way to locate these shrubby plants along roadsides: their small nuts are usually claimed by mice and squirrels long before they can be gathered by humans. Swelling oak buds will soon have hanging catkins, and catkins of hickories, including pecans, and black walnut will become evident as spring progresses.
Catkins, however, are only part of the nut story. They are the male flowers which shed their pollen, carried by the wind to tiny female flowers that often go unnoticed until the nuts they produce begin to develop. You’ll have to look closely at other buds to find the tiny maroon filaments that are the female flowers. Pollination isn’t guaranteed, even given the volumes of pollen that are generated. The wet 2019 spring is blamed for poor black walnut production that year as many believe that the frequent rains basically washed the walnut pollen out of the air so that it never reached the female flowers. There can be other complications. There are numerous examples of trees that require a second specimen in order to achieve successful pollination and produce fruit. For example, in pecans the male catkins on some trees will mature and shed pollen before the female flowers on the same tree are ready to receive the pollen. Fortunately, there are other pecan trees where the female flowers mature before the males begin to shed their pollen. As long as there is a mix of those trees in the landscape, there will be pecans produced on all of the bearing age trees.
Chinese chestnuts, an increasingly popular crop in Missouri, rely on insect pollination and their showy pale yellow male catkin flowers are alive with activity. Ironically, the female flower, tucked at their base, doesn’t attract insects so perhaps it is the motion of those tiny feet that loosens enough pollen grains to cause fertilization. Hmmmm…I’m going to explore this question further in my chestnut orchard this spring!