Trunk grafting – black pine
Grafting is one of the most useful techniques for developing bonsai from rough stock. A pine I have been working on for the past few years needs a few more branches before I can reduce it to its final height. To do this, I need to graft into the trunk.
Grafting requires a bit of homework for success. I highly recommend grafting with someone experienced or reading about it before getting started. Although I’ve been doing it for years, I still have a lot to learn. For pine, I’ve found that the end of winter is a good time to graft. I like grafting when it’s really cold out. On warmer days, sap can fill the cuts before the scion makes contact with the tree’s cambium layer. This year I repotted the day before grafting to further slow the flow of sap. Although this goes against common wisdom on the topic, I wanted to give it a try to see what happens.
For scions, I use branches that are one to two years old. Vigorous, but not too vigorous. I avoid using summer growth – the buds that grew after decandling the previous year. And typically, I used less vigorous shoots than the one below whenever possible, but these strong and compact shoots work too.
Scion – a shoot that developed last spring
The first step in preparing the scion is removing extra needles with scissors. 8-10 pairs of needles are usually enough to keep the scion alive. I’ll leave extras if the needles are short, like below, or fewer if the needles are long.
Scion after removing extra needles – 8-10 pairs are usually enough
Next comes the cutting. This is where studying a drawing of cambium layers comes in handy. Knowing where the cambium layer is helps when inserting the scion.
Scion – ready to graft
Here’s another view from the side to show the angles of the cut. Note that the top cut is a bit curved – that’s no good. Straight cuts fit snugly into the incision – curves can leave gaps that fill with sap and prevent the cambium layers from meeting. This can be fixed with another cut.
Scion – side view
After cutting the scion, I place it in my mouth to keep it humid. I’m careful not to touch the cut surface. I don’t know how much of a difference this makes, but it’s a comforting habit.
The faster the rest of the process goes the better as delays provide time for sap to flow. I use a 1/2″ chisel to make a vertical incision almost one inch long and maybe 1/4″ deep. This prevents the trunk from tearing when making the main incision. This can be done with a number of chisels, though the best come from Japan and are made specifically for the purpose. I try to use chisels that are the same width as the scion.
Making the incision
I make the cut fairly deep as it has to match the size of the cut on the scion. Here’s a view from the side.
Making the incision – side view
Next I remove the scion from my mouth and place it in the incision. This part can be tricky. If the incision isn’t deep enough, the opening may close a bit before the scion makes it inside. This will force the scion to stick out too far and the cambium layers won’t line up.
Scion sticking out too far
When the cut is made properly the scion fits snug.
Scion inserted to proper depth
Scion inserted to proper depth- front view
Next I wrap the trunk with grafting tape. I make it snug but not overly tight. This keeps the scion in place.
I wish I knew of a better source for grafting tape. I’ve used a variety of materials, but the one I like best comes from a Home Depot-like store in Japan. I try to stock up when I get the chance.
Grafting tape holding the scion in place.
The final step is covering the scion with a grafting bag that contains moist sphagnum moss. This provides extra humidity that prevents the scion from drying out before new vasculature can keep it alive.
You may notice that the trunk is cut right above the graft. I don’t expect it to grow – if no sap flows past the graft it’s unlikely to succeed. I prepared this graft last so I could take my time and get pictures along the way. I’ve left it in place to see what happens – it will be fun to see if it works!