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Orchid roots are often of great concern to
a grower. There may be too many roots, or too few. The roots
may be out of the pot or decaying within. Roots may not be growing
because they are either dead or quiescent in which case, no water
can be absorbed. Roots may be clinging to a clay pot making it
difficult to repot without damaging the lot. Roots can give a
grower a big headache! Here we see the copious rooting system
of Ascocentrum
ampullaceum.
What is a root? An orchid root is an organ
located above or below ground. All orchid roots are secondary
structures arising first at the protocorm stage.
Structure
- Orchid roots have an unique spongy outer layer called the velamen.
Velamen is not found around the growing root tip. Single-celled
root hairs arise from the outer layer. These are both absorptive
and the means by which mycorrhizal fungi can enter the root.
Here
we see the fungal structures within one root hair. Within
the root is the cortex, a layer several cells thick whose
function is storage of starch. Other cortical cells house mycorrhizal
fungi that form knotted structures called peletons which the
orchid ultimately digests. In the center of the root lies the
stele. Part of the stele can give rise to branching structures
including new roots or even shoots.
Function
-
- Roots can serve as absorptive organs. Here
we see the many
hairy roots of Phramipedium which grow in moist places near
water courses or equally well in moist compost in a container.
Roots are an anchoring device as in Tolumnia
guianensis. Adventitious anchoring roots form at every
node of Vanilla
planifolia. This plant will thrive if the roots are permitted
to take root on a mounting pole.
- Roots can serve as storage organs for monopodial
orchids such as Phalaenopsis and for terrestrial orchids such
as Diuris and Platanthera. Here we see the 'dropper' tuber of
Diuris oporina (taxonomic synonym Diuris punctata f.
blackneyae) forming in test tube culture. The
numerous root hairs mark this as a root.
- Roots can serve as primary photosynthetic
organs in leafless and in certain other orchids. In Encyclia (syn. Domingoa,
Homalopetalum) keinastii, seedlings
first form a large green storage root followed by a few very
tiny leaves.
- Roots may become an organ of vegetative reproduction.
While an orchid root lacks visible buds or nodes it may be capable
of branching or giving rise to root shoots as we see here with
Pogonia
ophioglossoides.
Determinate and indeterminate growth - Some orchids produce roots which last for only
one growing season. We see this with Pleione and Catasetum for
example. Sometimes the roots cannot branch or recommence growth
if cut or damaged which is the case with Pleione. Care must be
taken to ensure that root growth is undisturbed otherwise the
development of the new pseudobulb will be hampered. picture
Where roots last only one growing season, they can be safely
removed while the orchid is dormant and is being repotted. A
good example is with Catasetum where all soft spongy roots including
those growing vertically upwards can be removed before repotting
a dormant plant. picture
Perennial roots - Just because a plant has produced copious aerial
roots does not mean that we can trim them without consequence.
Roots of monopodial orchids such as Phalaenopsis and Vanda play
an important role in nutrient storage and water absorption.
Roots and repotting - Before repotting an orchid, endeavor to learn about
its growth habit. Epiphytic orchids typically have meandering
roots that cling to the substrate. These roots will also cling
to pots, baskets and even enter pots of nearby plants if you
let them. This Dendrobium hybrid is naturalized on a small tree.
The only safe way to remove it would be to grow it onto a plaque
placed near to the new shoot. Roots can be encouraged to grow
onto the plaque when once established and in sufficient quantity,
the plant and plaque can be relocated. picture.
Mounted orchids can always be grown onto another surface but
this takes time and patience. Here is Oncidium
longipes nearly due for growing onto a new larger mount.
Minimize root disturbance by repotting just before growth resumes
with the resultant production of new roots. Limit the damage
to existing living roots. With this plant of Dendrobium
oligophyllum, it would be almost impossible to remove old
medium without damaging roots in which case, the best approach
is to wrap fresh open medium around the root ball and let the
root ball expand. To keep plants healthy and virus-free, always
use clean tools, pots and fresh potting medium or mounts. Oncidium (syn. Trichocentrum)
stramineum.
That is the end of my presentation on roots.
You will note that I have stressed care of living roots for a
variety of reasons. Perhaps we can now discuss some concerns
you may have about orchid root health and well being. Are there
any questions?
janetteh
I have trouble with minature phal species which like to be mounted.
They either stay too wet or too dry. Have killed more than my
fair share of them. I have a Phal. chibae which I mounted on
a small branch and then stuck the branch in a pot of rocks. Some
of the roots are aerial and some have grown down in the rocks.
But after 3 years the plant is still alive (and blooming right
now). Would this be a viable solution for the other phal species?
MarilyninOttawa
I think that your solution is a good one. I have used or have
seen growers use a similar approach when it is challenging to
keep mounted plants moist enough. Phal roots were allowed to
dangle into pop bottles filed with very dilute manure tea. My
C. walkeriana grows happily on a rock with its 'feet' in moist
compost beneath. Orchids need moisture.
Violaprincess_in_San_Antonio
I have a question about Phal roots. I just recently rescued a
Phal from very bad root rot. There are a few roots growing upwards
out of a pot...they are green and healthy. There are almost no
roots left underneath. Should I mist the upward roots daily,
or loosely place moist sphagnum over them? I'm afraid these are
the only roots to take water into the plant. I grow Phals, I
have 2 Den Blue Violettas, and 2 Mtssa CM Fitch Izumi.
MarilyninOttawa
I am uncertain if the rotted roots are still in the pot. If so,
the plant should be repotted into fresh medium. Rooted roots
removed of course before repotting. Roots rot if the surround
is not sufficiently aerated. Use a more open mix. Water thoroughly
such that the water flows out of the pot. Mist frequently. You
can lay some New Zealand spagnum moss over the green roots.
Violaprincess_in_San_Anto
The rotted roots have been removed. These were some "Lowe's"
Phals...all 4 of them were severley rotten in the middle. I have
repotted them in sphag, I just wasn't sure what to do about a
few of the roots that grew upwards...they aren't going in the
pot!
MarilyninOttawa
If the roots are growing up out of the pot and not into the medium
then I suggest that the medium may be too dense (and water-retentive)
for your conditions. Use an open mix of coconut husk chips and
top with a loose layer of moss.
Violaprincess_in_San_Antonio
That is exactly what I thought. The roots were already growing
upwards when I got them (yesterday). They were potted in tight
dense moss with coco chips on top. It was very wet and looked
like it had been wet for a while. No air could have gotten in
there.
MarilyninOttawa
Sounds like you now have a possible solution. Best of luck with
these plants.
EDDIE_IN_GA
IS IT NOT TRUE THAT THE BETTER AND MORE ROOTS YOU HAVE THE BETTER
THE PLANT WILL GROW AND FLOWER
Violaprincess_in_San_Anto
I know that this is right...I have several Phals that the roots
have rotted off of, yet they are flowering with huge spikes.
MarilyninOttawa
The more roots the better especially in plants where the root
is the primary storage organ. The more growing roots, the more
surface area to absorb nutrients and water.
pecteilis_in_KY
Marilyn, there has been some discussion on OGD concerning the
function of fungus after the plant is out of the flask. Is the
fungus important to the orchid's uptake of nutrient?
MarilyninOttawa
Regarding the relative importance of mycorrhizal associations
ex flask, they do exist and may be important for the health of
some orchids. A host of different fungi inhabit orchid roots
but not all assist in the uptake of water and mineral nutrients.
If the fungi enter the cortical cells, form typical hyphal masses
in the cells which are later digested by the orchid then the
fungus is benefitting the orchid in some way.
janetteh
In your presentation you showed a picture of an orchid which
had come out of its container and said that you would pack media
around the pot in order to increase the size of the root ball
rather than disturb it. Would this also apply when you unpot
an orchid and there is nothing but a solid rootball in the pot?
Just plop it like it is into another larger pot?
MarilyninOttawa
Janette, a lot depends on the type of root, the relative root
health, and the medium. Sometimes you can wash some of the old
medium away from roots by using a jet of water. If not, or if
you suspect that the roots may be dead or mostly so, then you
probably should cut into the ball to check. Having a dense mass
of dead roots will not be too good for survival of the plant.
Otherwise, I would simply shake off old medium, plop the plant
into a larger container, and pour fresh medium around the root
ball. A lot depends on your assessment of root health.
In Catasetums, which form a dense ball of roots but these roots
are annual, living for one growing season only, I typically remove
almost all the dead roots before repotting. Repotting is best
done when new shoots and roots are just beginning growth.
janetteh
This usually occurs with cattleya alliance plants. From the outside
I can see no dead roots, and no media....which is a statement
on how often I get around to repotting some things. :-) But when
I have trying cutting into the rootball, most of the time the
roots are fine. If I can tell that there is a mass of dead roots,
I will remove them. But there are some times when it is impossible
to tell.
MarilyninOttawa
If it is impossible to tell but the plant appears healthy and
thriving, then pot on using an inch or two bigger diameter and
always loose fresh medium.
EDDIE_IN_GA
HAVE YOU READ ANYTHING ON EFFECTS OF ROOT HORMONES ON ORCHIDS
MarilyninOttawa
There is a product called keiki root which is a hormone preparation
designed to promote rooting of Phal keikis. You can experiment
with this if you wish. You might be able to stimulate root branching
but generally a healthy thriving plant will do just fine on its
own.
janetteh
Is there any reason why some plants will just not keep their
roots in the pot? Even when they have plenty of room to do so.
Phal. Golden Buddha comes to mind.
MarilyninOttawa
Epiphytic orchids produce roots that have a desire to wander
in search of more water, nutrients, etc. Many roots will stay
in the pot but other will explore. You can try to curb their
growth by gently turning them toward the pot but take care as
they are brittle. You can try using florist picks (filled with
water or very dilute fertilizer solution) over the tips of these
roots. It might slow their growth.
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