The How and Why of Grafting

 

 

Grafting is the process of creating a genetic clone or copy of an existing tree. There are several reasons why you might want to do this.  Some trees are hybrid in nature and won't come true from seed.  If you had an outstanding tree and wanted to make it available to the masses, it would have to be propagated by grafting or tissue culture.  Mature chestnut trees are very difficult to propagate through tissue culture or micropropagation, so at the moment grafting is still the most feasable means we have.  Another reason to graft a tree is simply because a tree is growing in a situation where it is not easily accessible.  This is a situation I have encountered frequently and will use this as an example.  

 

 

This is tree JAC-85.  You can read more about it in the tab labeled 'The Trees'.  There are a lot of reasons why I would want to use this hybrid tree in my breeding program, however there are 2 major problems.  1)The flowers and pollen are located  70 plus feet in the air.  The tree is located on a rocky slope where it wouldn't even be feasible to bring in a bucket truck.  2) The other problem being is that the tree is located some distance from my orchards.  Even if I could reach the pollen, there is the problem of coordinating the correct timing of trying to collect pollen, preserve it and get to my orchards at the right time.  

 

The situation is much easier if this tree is growing right in my orchard with the other trees.  This is where grafting comes into play.

In this photo you see David using a pole pruner on the Mountaineer chestnut tree.  Although the Mountaineer tree grows in the orchard, the flowers and pollen are much too high to be of use to me.  So like JAC-85, the answer is to make a graft and bring the flowers and pollen closer to me.

 

The pole pruner is a nice contraption to have.  There are several types on the market.  This one was purchased from 'Forestry Suppliers' and has wooden spruce sections that can be added as needed to lengthen the pole. This was used to collect wood or 'scions' from JAC-85 as well.  

The material you collect from your tree is call the scion.  It should be dormant, vigorous growth with healthy buds.  The method of grafting I use will require 1 or 2 healthy buds per graft.

A prepared scion, with wedge cut at the base.  This is not a scion from JAC-85, but is used to illustrate the technique.

The completed graft.  The scion is inserted into the prepared cut and held with a rubber band.  

The portion of the graft that provides nourishment and support to the scion is called the rootstock.  Chestnuts graft best on their own seedlings to prevent the chances of graft rejection.  Most people will graft onto established trees or seedlings in the field.  I have modified a method where I graft onto seedling material inside.  This is a type of bench grafting.

The prepared rootstock.  The sprout (epicotyl) has been removed where it emerges from the root (hypocotyl).  A vertical cut is made into the root to hold the scion.  The end of the root is also trimmed to promote lateral root growth.  I have learned to do much of this cutting on a tongue depressors, or jumbo craft sticks to avoid cutting my fingers. 

The completed graft is placed in a bag of moist peat moss.  The graft union is buried.  Make sure the peat is damp, but not overly wet.  The plastic bag acts as a mini greenhouse.  Once the graft starts to leaf out, it must be slowly  acclimated or the graft will die from the shock.  I accomplish this by punching small holes in the bag over the course of several days, then opening the bag slowly over several more days.  

The graft leafing our nicely after 2 - 3 weeks.  Notice the moisture clinging to the sides of the plastic bag.  This makes a great 'poor mans' greenhouse.  I usually place 2 grafts per bag. With practice, many grafts can be done in a short time.

A box of completed grafts that have hardened off nicely and are adding additional growth.  These will be hardened off further outside and then transplanted.

Tree JAC-85 providing pollen while it is only 4 - 5 feet tall. This is much easier to work with as opposed to a tree that is 70 - 80 feet in height.The scion still 'thinks' it is a 60 year old tree and that is why grafted trees bear much earlier than seedling trees.   

David staring up into a healthy grafted JAC-85 roughly 10 years ago.  Both he and the tree have continued to grow well.