Mastering the fine art of grafting

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NEW PLANT: Various methods are available for reproduction when seeds are not reliable.

HYBRIDISATION and breeding work have created a whole new world of plants over the years. Today we can grow cabbages, rock melons, longans and a whole range of highland agricultural products in low altitude tropical conditions. This is thanks to the hard work of researchers and agriculturalists.

This week I thought it would be interesting to go through the basic points of grafting. The basis of the art lies in the vascular cambium cells, which are generative cells, like terminal buds that keep undergoing meiosis and mitosis for new growth.

The botany of dicot plants gives us the advantage of cambium cells just below the bark of the stems or branches. Grafting is done by carefully removing the epidermal bark with a sharp knife and then inserting the scion into the cut section of the rootstock plant. The newly grafted stem is then tied and kept airtight with a plastic cover.

Different types of grafting

Cleft graft — This method of grafting for both flowering and fruiting trees is used to change the variety. Cleft grafting is also used to propagate varieties of plants that are difficult to root. It can be done on the main stems or on lateral or scaffold branches. The rootstock should be less than four inches in diameter and straight grained. The scion should have a few buds ready to sprout into new branches and leaves. Insert the new variety into the cut slit on the rootstock and apply wax to keep it airtight. This can be used successfully on papaya trees to produce specific fruit quality demanded by consumers.

Bark graft — This is used on flowering and fruiting trees to get a new variety by grafting a smaller scion onto a much bigger stem as rootstock. Cut a cleft on the side of the sawn stem and then insert the scion in place and seal with wax. The advantage is we can have several scions planted onto the old stock.

Side veneer graft — This method is popular for attaching a new variety onto the stem of another tree. We often see the results on multicoloured bougainvillea flowers or even Chinese orange trees that are full of fruits for Chinese New Year imported from mainland China.

Splice graft — This is a slanting cut on the rootstock, which is joined by the scion of a new variety that is exactly the same size on top. This is good for herbaceous materials that knit easily. It is strictly a method for young immature plants with stems of less than half an inch in diameter.

Saddle graft — This is an easy method to learn and master quickly. The stock can be field grown or potted. Both the rootstock and the scion should be of the same size — preferably less than one inch. The art is in the preparation of the cut and the fit of the two parts together.

Aerial layering

This is a centuries old method to reproduce new varieties of plants efficiently. It is a technique used for rooting branches attached to a parent plant and an alternative method for any plant that is hard to root at soil level. In tropical countries, aerial layering can be performed at any time, but in cooler climes, it is best done during early summer or when the flowering season has just ended. Rooting must be done in autumn and the plant established by winter.

This method is more suitable for shrubs and trees that have stiff branches and stems. Choose healthy stems with sturdy new growth, but they should not be too old.

Firstly trim off any leaves and side shoots below the growth point. Then use a sharp knife to cut an angled wound unto the stem. Then aid the formation of roots around the cut by dusting with rooting hormone. Next, prevent the wound from healing over instead of forming new roots. Add sphagnum moss or a small stick to prop open the wound without tearing the slice open.

Slip a clear plastic bag — open at both ends — over the cut and secure it well just below. Fill the area around the cut with a moist sphagnum moss. Pack it firmly around the stem and secure the upper ends with garden ties after sealing the rooting medium inside. Having an airtight package is important to allow the cut to
generate new roots.

Budding

This method is used to change the variety or even introduce a new strain in terms of yield or production. It is most commonly used in fruit trees like rambutan, durian, oranges and a host of other plants where seeds are not reliably of the same quality as parent trees. Do note that seeds are even more unreliable when it comes to hybrid plants.

The change of parental characteristics becomes apparent with the second generation. Get selected clones like rubber or durian and then bud them onto stock seedlings. At times mother plants are also used as they take on the new buddings with greater ease. Some species of citrus are notoriously difficult to bud if we choose the wrong seedlings.

Maintenance work

Periodically check the seal and ensure rainwater does not penetrate the plastic bag or it may cause rot or mould and will fail. Use waterproof tape or ties to secure the bag. If it becomes too loose, the layered areas may also dry out and die. Once the roots are well formed, cut the branch just below the lower tape wrap and remove the plastic for planting in a small pot.

Some aerial pruning of the leaves may be needed to balance the need of water absorption by the new roots and the rate of transpiration from the leaves, thereby reducing the loss of water. Cut off about half of the leaves. The right start will see the new plant established well.

Always sever or saw off old stems above the union of budded plants or else you will end up growing the old variety.