After the grafting process is done, the cuttings go through a process called callusing. A callus is a tissue growth produced by the plant where it has been injured. In our case, there is an injury at the graft union (on the rootstock and the scion), and at the bottom end of the rootstock. Callusing is an essential part of bench grafting. No callus, no graft or roots. When the plant sustains an injury, it produces this growth of undifferentiated cells (callus) to heal itself. These cells are called undifferentiated because they can transform into any part of the plant (roots, stem, bark, etc.). For the graft union specifically, it will act as a weld between the two parts (rootstock and scion) that will eventually become lignified into one piece. At the bottom end of the rootstock, these cells will become roots.
Nifty little creatures aren't they?
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| It will go from this... |
There are a few things plants need to produce callus. When performing the graft, the plant material in dormant. The first thing to do is to shock them out of dormancy by giving them heat and humidity. The ideal temperature for vines to produce callus is around 27 to 29 Celsius (~80 to 85 F).
At these temperatures, a vine cutting can produce callus in as little as a week, but it typically takes two to three weeks. For ideal humidity, I like to put the cuttings in a sealed plastic bag filled with very moist (but not wet) peat moss. I found that for optimal results, the humidity level has to be just right. I simply add water to the peat until it just starts releasing water when squeezed tightly into a ball.
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| ... to this! |
And mix it very well so it is evenly damp throughout the bag. Then put cuttings in and seal.
The next step is to keep those cuttings warm and moist for the next two weeks. There are many ways to do this. Nurseries use ''sweat boxes'' which are more like heated insulated rooms with shelves where they store their plants. I built a miniature version of this with the smallest space heater I could find, and the biggest Rubbermaid container could find (make sure that the heater has a thermostat control!!). I put the space heater inside the container, set it to 85F, and voila! Of course, there could be many variations of this. The goal is to keep the cuttings at that optimal temperature the whole time with as little variation as possible.
After 2-3 weeks, you should have abundant callus growth and even roots already started. Next, dip the top of the graft (tape and all) in the melted wax making sure to cover the graft union completely and dip in cold water right after to cool down. I use a ''bain marie'' to heat up the wax. Don't let the wood in the hot wax too long or it will damage the buds. This wax will seal the graft and keep it hydrated while the wound heals and until the plant can hydrate itself. The residual wax layer will eventually fall off on it's own. You may notice that some of the buds will have started growing and some will even be up to 2-3 inches long (they will be white due to lack of light). They are very fragile at this point so handle them carefully, they also need to be dipped in the wax because they would just dehydrate and die. If for some reason one breaks or dies, a secondary bud will usually start growing to take its place. Although this will take a lot more energy out of the plant, the cuttings usually survive and once a root system develops, they will quickly recover.
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| Indoor garden with baby vines. |
Its now time to pot these cuttings and gradually introduce them to the light. Gradually is the key word here. Put them outside in the sun and they will surely die from shock, and the week shoots and leaves would burn. I like to use an indoor garden light with a high pressure sodium bulb. They can be bought at any hydroponics store. Fluorescent fixtures, although less intense, can also work and , of course, a sunny window will do the trick if you only have a few plants. I like the high pressure sodium light because it is the most intense of them all (but not scorching like the sun...). With that setup, I find I can have the best control over the growing conditions. As you can see on the picture, make my own pots using vinyl ''downspout'' used for the fabrication of eaves through. I like using this material because I can make my pots high enough to bury most of the stems of my cuttings. Regular pot are either not high enough, or to wide, and not space efficient. Another advantage is that they are square so there is no loss of space between pots. So I cut them to length and then use screen material (used to repair window screens) secured with duct tape to close the bottoms. All of this can be found at any hardware/home reno store and is rather inexpensive.
The plants will start growing more and more vigorously as the produce more roots. After a few weeks, they will look like this...
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Another chip bud (sill wrapped).
You can see the callus through the tape. |
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| Chip bud with callus growth. |
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| Happy vines ready for the outdoors! |
Once the plants look healthy, I start taking them outside in a shaded area for a few hours a day. And this is very important, they are not ready for full sun yet. Remember, even in the shade, they are now exposed to more light then any artificial lighting can produce. I usually take them inside for the night though. These plants were started in mid March and we are now close to the end of April/early May and the nights can still be too cold. After a few weeks outside, the plants are gradually exposed to direct sunlight and are now hardened.
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| They can't have enough sun now! |
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| Graft union. Almost healed... |
The vines are now ready to be transplanted. They can be put in their permanent spot right away if late enough in the season. Frost could be devastating at this stage (well... at any stage really!) I chose to put them in larger pots (1 gal. pots) because my planting site was not ready yet.
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| Nice roots at the bottom... |
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| Grafted Riesling vine after a few weeks outside. |
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| Grafted Chardonnay. |
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| Ready for their new home! |
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