by Krystal Folino and Bill Mee
Lychee Tree Root System and Development
When we think of lychee trees what we think of is the spectacular
evergreen foliage and the clusters of delicious red fruits. What often
is not considered is occurring below ground in the root system of the
tree. A healthy root system is essential for growing a healthy lychee
tree. Understanding how the lychee root system works can help you grow
more vigorous and productive trees.
Two Types of Root Systems:
seedlings and grafted tree that have reached maturity have well
developed vertical tap roots that can extend a few meters down into the
ground towards the water table. These deep dwelling tap roots are
accompanied by some lateral branching surface dwelling roots.
layered trees have no main tap root and instead have entirely shallow
lateral branching root systems often called skeleton roots. These
skeleton roots have their entire network in the top layer of soil to a
depth of about 8 inches.
The lateral absorptive roots of a lychee
tree extend out to about the drip line of the tree canopy. The diameter
of the canopy is a good indicator of the extent of the root system.
clear above ground indicator of a healthy root system is the ability of
a tree to resist lateral pressure, such as wind. This is especially
true in small trees. Trunks that easily flop from side to side or feel
loose, when they are pulled on, are either not healthy or lack an
adequate network of roots to support the tree.
If some of the
root system is exposed, mature healthy roots should be flexible and
should display a light green when gently scraped. The smaller branching
root tips should be whitish and flexible and should not easily fall
apart when tugged.
The root system of a lychee tree typically
experiences 3 climaxes of growth each year. Not surprisingly, these
root system growth events seem to occur when the surrounding soil is
warm. They occur from:
mid-May to June
July to August after harvesting
Mid-October when autumn shoots get matured
How the Lychee Root System Works
lychee tree has two basic functional systems: the canopy and the root
system. It is important to understand the interactions between these
two systems and the role of these systems in the health of lychee trees.
canopy, consisting of branches, stems and leaves is where
photosynthesis occurs. The products of photosynthesis - sugars and
amino acids - are conveyed through the bark to the roots, growing tips
of stems and leaves, flowers and fruits.
The root system is
where water, minerals and nutrients are absorbed from the soil and
conducted to all other parts of the plant. Gas exchange also occurs in
the root system.
The area directly adjacent to the absorbing
roots is called the rhizosphere. In a natural, undisturbed forest
environment this area is composed of weathered minerals and
deteriorating organic matter. Living within this mix are populations of
earthworms, insects, diverse invertebrates, protozoa, bacteria and
These organisms participate in the breakdown of organic
material into essential inorganic elements that may be used by forest
plants. Bacterial microbes break down and solubilize minerals such as
phosphorus for plant availability, recycle nutrients and help to
protect the plant from soil pathogens and nematodes.
Mycorrhizal fungi colonize the fine absorbing roots of trees to derive
most, if not all, of their food supply (carbohydrates, vitamins and
amino acids) from the roots of the plant. In return the mycorrhizal
fungi aid in the growth and development of their host tree by
significantly increasing the absorptive surface area of the roots, as
well as assisting in the decomposition of organic matter.
Mycorrhizal fungi enhance the tolerance of plants to drought, seasonal
temperature fluctuations and pH balance as well as minimizing the
negative effects of transplant shock. Mycorrhzzal fungi also help to
protect the plant from harmful diseases and pathogens and reduce the
dependency of plants on supplemental fertilizers.
soils, such as what we purchase and use for growing plants in
containers or in man-made or urban developed landscapes, these natural
soil components are missing and should be replaced for healthy plant
Root shading and cooling:
late Spring, Summer and Fall of the sub-tropics the shallow root system
of a lychee tree is exposed to the daily cyclical extremes of heating
and cooling. This stress is especially pronounced during the mid summer
post harvest months.
Although lychee trees need partial to full sun,
the roots prefer to be shaded for optimum health and growth. The
hemispherical habit of growth and shape of the lychee tree naturally
keep the root system shaded under the canopy.
Mulching provides a
excellent way of maintaining a healthy growing environment around the
absorbing roots of a lychee tree. Mulch retains moisture, promotes and
created a home & food for beneficial soil bacteria and mycorrhizal
fungi, earthworms, insects, protozoa and effectively shades the root
system from direct exposure to the sun. This helps to regenerate the
soil around your lychee tree to approximate forest soil characteristics
which are missing in artificial landscapes.