Waikato

Graft­ing joins the roots of one tree with the branch of another, and bring­ing two trees to­gether into one can give you the best of both.

NZ Gardener - - Contents -

Sh­eryn Cloth­ier’s tips on graft­ing trees

It is the root­stock that de­ter­mines how the tree grows. It de­cides how tall it gets, how it branches, what soils and cli­mate it likes, how soon it will pro­duce fruit, the qual­ity of the fruit and what pests and dis­eases it will re­sist.

The scion (which con­trib­uted the branch to the part­ner­ship) de­cides what type of fruit it will pro­duce, so a good fruit can be repli­cated ex­actly.

Just about ev­ery fruit tree you buy is a grafted tree.

And a good nurs­ery will tell you what the root­stock is.

Ex­cept for lemons, most of our citrus is grafted onto Pon­cirus tri­fo­li­ata root­stock. Tri­fo­li­ata is re­sis­tant to the citrus tris­teza virus that has been the death of mil­lions of citrus all over the world. It is also cold hardy (in citrus terms, New Zealand is cold) and pro­duces large amounts of high qual­ity fruit. Tri­fo­li­ata is also semi-dwarf­ing – the tree does even­tu­ally get to full height, but it takes longer to get there.

Peaches, nectarines and apri­cots are of­ten grafted onto pre-grown stones so they fruit sooner, but I sug­gest these trees are best grown from seed. I find that the stone-grown trees are very sim­i­lar to their par­ent, and a seedling will start pro­duc­ing fruit when about four years old.

Plums are usu­ally ei­ther on My­robalan (vig­or­ous and tol­er­ates heavy soils) or Mar­i­ana (dwarf­ing) roots but once again, seed-grown or cut­ting-grown plums on their own roots do well in New Zealand.

Pears are so large they are usu­ally grafted onto quince to dwarf them, but since this is a dif­fer­ent genus, there can be com­pat­i­bil­ity prob­lems af­fect­ing the tree in later life. Of­ten, an in­ter­stem of a com­pat­i­ble pear va­ri­ety is used. In­ter­est­ingly, seedling-grown pears live over 300 years, while pears grafted on quince sel­dom live longer than 40 years.

Ap­ple root­stocks have been well­re­searched for com­mer­cial pur­poses. East Malling Re­search Sta­tion, a hor­ti­cul­ture and agri­cul­ture re­search institute in Kent, Eng­land, iden­ti­fied the prop­er­ties of a range of ap­ple root­stocks in the early 1900s, and M9 and MM106 are two com­monly in use in New Zealand to­day. M9 is dwarf­ing – grow­ing to about 30 per cent of nor­mal height and MM106 is a heavy and early pro­ducer that grows to 70 per cent of full height.

The most ob­vi­ous as­pect of any root­stock is its ef­fect on plant height.

Com­mer­cially, dwarf­ing root­stock is now pre­ferred as it re­duces prun­ing and pick­ing costs. But a small tree also has a small root zone, which means it needs sup­port against wind and is un­able to source quan­ti­ties of mois­ture and nu­tri­ents. This is fine for or­chardists who grow their apples on wire frames and reg­u­larly wa­ter and fer­tilise, but for the easy-care home or­chard, a vig­or­ous tree will grow a large root base, an­chor­ing it­self and seek­ing out its own food and wa­ter.

Of all the fruit trees, apples are the eas­i­est to graft. If you have a favourite ap­ple tree you wish to repli­cate, se­lect your scion wood now (in mid­win­ter) and keep it re­frig­er­ated for graft­ing in spring. Robert and Robyn Guy­ton’s Open Or­chard Project also sells a range of her­itage scion wood

from South­land or­chards.

The scion wood should be a year old.

It should be about pen­cil thick­ness with three to four good plump buds. Cut and store in a plas­tic bag with some damp pa­per tow­els or sphag­num moss to pro­vide mois­ture – you don’t want it dry­ing out. La­bel and seal the bag well and store it in the fridge. The fridge is per­pet­ual win­ter for the scion wood.

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Graft­ing new scion wood onto an ex­ist­ing tree is called re­work­ing and pro­vides a strong, es­tab­lished root base for the new growth. This tech­nique was used ex­ten­sively in ki­wifruit or­chards to quickly re­place va­ri­eties at­tacked by PSA.

Check the Events page: Tree Crops As­so­ci­a­tion and other lo­cal groups of­ten host graft­ing work­shops.

Bind the union tightly.

A two-year-old union still vis­i­ble.

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