by William Mee
Grafting and Grafted Lychee Trees
I am often asked about whether grafted lychee trees are better than
air-layered trees. It depends on the following list of criteria:
The variety of lychee you wish to grow.
The location you wish to grow that particular variety.
The habit of growth you wish to achieve.
standard commercial process for propagating lychee trees is via the
method known as air-layering or marcotting. This involves girdling a
strip of bark and interrupting the cambium on a nicely shaped branch.
High volume air-layer production is usually applied to branches
½ - 1 inch in diameter. The cambium is the vascular plant tissue
that supplies the roots of the tree with nutrition that has been
photo-synthesize in the leaf canopy of the tree. A bolus of moist
rooting material contained in a sheet of foil or plastic is applied
around the bare strip. Over a period of 7 - 10 weeks roots form in this
foil container. When the foil ball is fully filled with roots the
branch is cut off below the strip and planted either in a container or
directly into the ground.
An air layered tree, unlike a grafted
tree, does not possess a tap root. Instead, an air-layer will form a
relatively large spreading root system. This larger root system will
lead to accelerated growth. In a grafted tree, a cutting of a
particular variety (the scion) is attached to an already established
root stock. The graft union involves getting the cambium of the scion
to align with the cambium of the rootstock and then sealing this union
from exposure to bacteria and pests. Different methods of grafting can
be used, such as veneer grafting and chip budding, but the most common
graft type is known as a cleft graft. If all goes well the union of the
scion and rootstock heals and you end up with one variety of tree
growing on another variety. The root stock may be an air layer of a
common variety or it may be a seedling. Generally speaking, plant
varieties are grafted onto a seedling rootstock that is best suited for
a specific soil growing condition. In the case of fruit trees such as
apples, peaches or citrus the rootstock is selected to be resistant to
soil pathogens specific to a geographical region. Usually, rootstocks
are selected for their resistance to soil nematodes and fungi.
lychee trees are difficult to graft. This means that unless great care
and excellent grafting technique are applied the graft will not take.
So, for a lot of grafts you may end up with no results. The end result
of this is increased expense and from the large scale growers
perspective this is not so desirable. On the other hand if you want a
tree that is dwarfed (you have a very small yard or a container)
grafting may be a desirable alternative.
There are certain
varieties of lychees that do not tolerate soils with a high pH. This is
typical of limestone soils such as those found in southern Dade County,
Florida (the county where Miami is located). One variety that will not
grow well in lime rock is the Emperor. The Emperor is a unique lychee
that produces an enormous, juicy fruit with a tiny seed. To grow an
Emperor in limestone soils you must graft the tree and the end result
is a dwarfed slow growing specimen. If you grow an Emperor in Western
Broward County where the soils are old Everglades muck then you can
plant an air layered emperor directly into the ground and it will grow
magnificently. This is because muck soils have a very high organic
content and the levels of humic acids give the soil a lower and closer
to neutral pH. Lychees thrive in more acidic soils with a high organic
content. This is one of the reasons that mulching around lychees
greatly improves their growth rate and overall health.
answering original questions if you had asked what is the best way to
propagate Brewsters and Mauritius trees for planting in Western Broward
I would say air-layering. If you want to grow an Emperor tree in south
Miami it needs to be grafted.