Interstem Grafted Apple Tree Update, Year Four

UPDATE: See my video series on Inter-stem grafting apples here!

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It’s been 4 years since I grafted my first interstem apples.  They were in the nursery for a year, and have been in the ground in permanent locations for 3 years.  This is an update on my experience and thoughts so far.  (Read the original post here)

 

A couple paragraphs for those who aren’t familiar with interstem trees: An interstem (a.k.a. double worked, archaic) tree is one that has an extra stem grafted between the rootstock and the upper portion of the tree.  Sometimes the interstem (the stem between the roots and the tree) is there for the sake of compatibility and can be used when the fruit variety is not genetically compatible with the rootstock, but the interstem is compatible with both the top and the rootstock…. think of a kidney transplant, the donor and recipient have to be compatible or the graft will be rejected. Often though, and in my case, the technique is used to dwarf a tree. One problem with dwarf rootstocks is that they are weak.  Sure they are small, which is what we want, but so are the roots.  Interstem grafting allows us to select a large vigorous rootstock, that would normally grow a large vigorous tree, for the roots and a weak interstem to dwarf the tree… small tree big roots.  That means, no staking of the tree, which would be required for a weak dwarfing stock.  They also need less water.

Interstem dwarfs on the left at 8 foot spacing, and oblique (diagonal) cordon row on the right, tresllised, 18 inch spacing about 7 feet tall.  Both will outperform standard trees in production per unit of land.  The oblique cordon are on bud 9 however, and require more water than the interstem trees which have a base of possibly the most drought tolerant of the common apple stocks, M111 and interstem of bud 9.  The largest looking tree there on the left has a short interstem, and is also growing near a waterline leak.

Drought Tolerance:  My primary motivation for grafting interstem trees has been drought tolerance combined with dwarfing, a pairing which I don’t know of any other means of attaining.  I’ve had a few of the trees get a little crispy in the end of summer, but over all, I think they are performing much better as m111 / bud 9 interstems than they would on any stand alone dwarfing stock.  I do water them occasionally, but not a lot.  I probably should ideally water a little more, but I want them to grow up tough and self sufficient, not expecting a drink whenever they want one… tough love.  There is a second row of interstem trees that I will probably move, or just remove, which are not cared for nearly as well as the main row along the driveway.  Most of these outliers have survived and, although they are not doing great, I doubt many would have survived the droughty conditions they are growing in if they were on a straight dwarfing stock like MM109 or bud 9.  I probably won’t water any of the interstems this season since my spring is lower than it’s ever been at this time.

Interstem Grafting of Apples: small trees, big roots

In which I use the tricky manipulation of grafting 3 different apple varieties together to create trees that are small yet drought resistant

UPDATE: to see my new video series on interstem grafting, click here!

Inter-stem trees sprouting on in the nursery row.  Note two bandages on each tree.

THIS BLOG IS RETIRED, I’VE MOVED TO SKILLCULT.COM   

ALL THE OLD TURKEYSONG POSTS ARE THERE AND MORE, CHECK IT OUT!

A long time ago fruit tree grafters selected certain rootstocks that would create smaller trees for small gardens and special purposes like espalier training.  Dwarfing rootstocks are naturally small varieties of trees that confer their diminutive size to the fruit varieties grafted onto them.  Early grafters had to make due with a limited selection of these dwarfing stocks, but these days there are ever smaller and more improved dwarfing rootstocks selected for size, rooting characteristics, disease resistance and ability to confer early fruiting to the variety grafted to them.  Some of these modern stocks make trees of only a few feet in height.  Last year I picked apples in a 30 year old orchard that had been grafted onto the dwarfing rootstock Malling 7.  The trees were only about 7 to 8 feet tall making picking and maintenance very easy.  These trees were also heavily loaded with fruit.  One drawback to using dwarfing rootstocks is that they tend to be shorter lived than normal sized fruit trees.  I’m planting trees for posterity and not just for myself, so I usually gravitate toward larger and healthier stocks.  After observing these ease of handling with these small trees and noting that they seemed to be doing well after 30 years I figured maybe there was a place for some dwarfed apples here.

Dwarfed trees may tend to be shorter lived, but they bear at a younger age and can give higher yields per acre when planted at closer spacings.  That’s a nice advantage.  I decided to put in a group of dwarfed trees grafted to varieties suitable for hard cider making.  First I looked for a good dwarfing stock in the 9 to 12 foot high range and decided on the newer Geneva 30 rootstock.  Alas, everyone seemed to be out of it because it was late in the season.  Then I got onto the idea of using an inter-stem.

In inter-stem grafting (also known as double working and interstock) a normal sized vigorous rootstock is used for the roots of the plant, a second variety of dwarfing rootstock is grafted on top of that, and the fruit variety to be grown out is grafted on top of the dwarfing inter-stem.  The result of this strategic placement of genetic materials is a fruit tree of the variety you want, dwarfed by an inter-stem but with a full sized root system to feed it.