Grafting Trees and Tomatoes

This grafted tomato plant is doing very well after only 16 days. Pics: Chris Kafer

This week a few people have asked me why shoots are growing from the base of their ornamental trees.  They are a bit bemused because the leaves coming from the fresh shoots bear no resemblance to the top growth.  This growing of two types of trees on one stem happens because of a process called ‘grafting’.

Grafting

Grafting has been practiced for thousands of years. It was in use by the Chinese before 2000 BC. This is a horticultural technique whereby tissues from one plant are inserted into those of another so that the two sets of tissues join together.

In most cases, one plant is selected for its roots and this is called the stock or rootstock. The other plant is selected for its stems, leaves, flowers, or fruits and is called the scion or cion. This is the bit that has the desired fruit, leaves and flowers. There are a few different methods such as stem or bug grafting.

Fruit trees are a popular grafted tree and are god because:

• If they were grown on their own root system, many would be too vigorous.
• Cultivars will not usually come true from seed.
• A fruiting plant can be produced in a shorter period of time.
• A weak-growing cultivar can be invigorated and produce far more fruit.

Ornamental shrubs and trees are also grafted, especially when:

• It is difficult to propagate by other means, such as cuttings or cultivars do not come true from seed.
• It’s needed to strengthen plants that grow weakly on their own root systems.
• When we need to  produce a larger flowering plant in a shorter period of time.

Acer palmatum, Hamamelis, Wisteria, Thuja and Picea are examples of commonly grafted plants.

Most apple trees in modern orchards are grafted on to dwarf or semi-dwarf trees planted at high density. They provide more fruit per unit of land, higher quality fruit, and reduce the danger of accidents by harvest crews working on ladders. Care must be taken when planting dwarf or semi-dwarf trees. If such a tree is planted with the graft below the soil, then the scion portion can also grow roots and the tree will still grow to its standard size.  The roots of the stock plant will also grow stems, especially if they are damaged by mowing around the tree. Some cherry tree growth can appear metres away from the main trunk. 

Re-use

All of the main rootstock growth can be cut of and rooted again.  If you ever fancy doing a bit of grafting yourself, you will have the rootstock to play with. Probably better just to compost them though.

Protection

In areas where soil-borne pests or pathogens would prevent the successful planting of the desired cultivar, the use of pest and disease tolerant rootstocks allow the production from the cultivar that would be otherwise unsuccessful. 

Joining together

Tree branches and more often roots of the same species will sometimes naturally graft; this is called inosculation. When roots make physical contact with each other they often grow together. A group of trees can share water and mineral nutrients via root grafts, which may be advantageous to weaker trees, and may also form a larger rootmass as an adaptation to promote fire resistance and regeneration.

A problem with root grafts is that they allow transmission of certain pathogens, such as Dutch elm disease. Inosculation also sometimes occurs where two stems on the same tree, shrub or vine make contact with each other. This is common in plants such as strawberries and potato.

Grafting Tomatoes

Tomato Grafting has been utilized worldwide in Asia and Europe for greenhouse and high tunnel production and is gaining popularity in the rest of the world.  Typically, stock or rootstocks are selected for their ability to resist infection by certain soilborne pathogens or their ability to increase vigour and fruit yield. The scion of the grafted tomato represents the upper portion of the plant and is selected for its fruit quality characteristics. There are several methods for grafting tomatoes , most of them are pretty difficult and require really clean equipment and perfect growing conditions. 

    

The main reason for grafting is soil borne disease resistance.  Many desirable tomatoes are susceptible to pathogens like Fusarium, Verticillium and nematodes.  These can be devastating pathogens that lead to total loss. Many commercial hybrids have been bred to resist these pathogens.  Great for commercial growers but not so great if you want to grow heirloom varieties which typically lack any disease resistance, but some argue are the tastiest.  I have loads of self-set ones in the tunnel again this year (my favourite weed) so I am going to have a play. You never know it might be a new variety, although maybe not as strange as the pomato. These are a grafted potato rootstock onto a tomato top. Two crops in one.