Monday 2 April 2018

Bench grafting

While I did do some field grafting and budding at Wisley, I had never done any bench grafting. The opportunity to practise, however has come now, as I am studying to complete my RHS level 3 Diploma in the Principles and Practices of Horticulture, and grafting is an examinable skill.

Grafting is mainly done at the earliest time of spring, just before bud break, and in the late summer, when new wood has had time to ripen stiff enough.

In order to prepare us for the July test of budding and side veneer grafting, we got some training in whip and tongue, which is based on the same basic cut.

The most important requirement for grafting is a sharp knife, without which you have no control of the cut. To sharpen the knife you need a water or oil stone. I have an Arkansas oil stone that is just wide enough. After oiling the stone, you have to place the blade whole on the stone, finding the original sharpening angle of the bevel. You only sharpen the bevelled side of the blade, and you have to get the angle right, or you won't get it sharp.

Finding the sharpening angle
on the bevelled side

Once you settle on the right angle, place the other hand on the tip of the blade and pull towards you, with a steady motion. Then you start again,  repeating for five/six times. It has to be shave-proof!
To finish off, remove the burr on the other side of the blade, by placing it flat on the stone and using gentle round motions.

Once you have a sharp knife, you need to hold your wood safely. I have previously nipped my fingertips and therefore find it easier to wear preventative plasters (namely on the thumb of the knife hand), but we were taught a foolproof way to hold the wood to avoid that.

Hold the wood close to where you are going to make the cut, palm down.

Then grab the blade quite close, to wield control, and you are ready to go.

The basic grafting cut is a sloping cut that leaves you with a flat surface, some 2.5 to 3 cm, across the wood. To achieve that, you have to slide the whole blade, bottom to tip. You start by placing the bottom of the blade on the top side of the wood that you are holding, close to your hand, at some 30 degrees angle, then you pull it towards you, sliding it in the wood towards the bottom and all the way to the tip, like below.

You start with the scion wood (the 'stick' of wood that you have chosen for a specific cultivar of plant that you want to grow - taste, appearance, whatever that is for) and need a clean cut: as flat a surface as you can muster, as it will need to adhere perfectly to the matching cut you are going to make in the rootstock (which you have chosen for the qualities of the roots i.e. disease resistance, dwarfing stock etc). You can tell if the cut is flat when you place it against the blade of the knife.

A flat enough cut

I did practice a few cuts on Cornus stems

Once you are confident on your cut, you can decide to go for it. I have described the procedure for whip and tongue grafting before, so I won't repeat it, but there were a couple of different things in bench grafting, which I noticed.

First, the scion stick is longer, 15-20 cm with at least five buds: you don't risk knocking it off that much at a desk as you do when standing over grafts made in the field. And, because I read in my propagation books that the healing process starts in the scion wood rather than the rootstock, it makes sense to have more wood = more stored energy available.

The other difference is in the tying of the graft union. We used a simple elastic band instead of grafting tape, and we started at the top of the graft going downwards, which is really easy. Again, it makes sense - in the field, you are standing over the graft and if you start at the top, the scion stick is in the way and you keep knocking into it, but here... super easy!

Test whip and tongue on willow
The result of my efforts: 2 Spartan apples
on M9 stock

I went home to pot my new apples up!
The next step, grafting on the plot where 14 rootstock plants await...

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