Hibiscus Disorders
&
Environmental Influences

Bud Drop
Premature Floral bud drop of Hibiscus is usually associated with Bugs, Hibiscus Beetle & Caterpillars which attack these buds in their early development.
Once the flower bud has developed to the point of opening, they appear not to drop as readily
despite continued insect attack.
At times when temperatures are excessive this will also cause some bud drop.
The lack of production of flower buds can be sourced to excessive use of Nitrogen which stimulates vegetative growth at the expense of flower bud formation.
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Bud Drop Of Hibiscus
 
Size: X 2.0
Note: the point at which the bud departs from the peduncle (stalk) is called the abscission layer

 Chlorosis

Not usually a major problem with Hibiscus as it can be with other plants such as Citrus & Camellias.
In severe cases could be an indication of the inability of the plant utilize iron due to an alkaline soil.
This would be indicated by interveinal chlorosis
Yellowing of growing tips & or white flecking on the opening flower buds may be an indication of glyphosate toxicity (Roundup herbicide damage).
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Chlorosis Of The Leaf
Size: X 1.0
Note: When chlorosis occurs in the odd leaf it is not a real concern & by the removal of this leaf will be all the treatment necessary.
 


Frost Damage
Hibiscus rosa-sinensis cultivars being a sub tropical plant are sensitive to frost.
Hibiscus plant tissue contains very high concentrations of solution which carry nutrients &  is commonly called sap.
When this sap is subjected to freezing conditions even for very short periods the solution freezes & consequently expands & in doing so ruptures living plant cells destroying their ability to function.
Causing irreparable damage to the plant parts subjected to the freezing temperatures.

In some cases the frost or freezing conditions may be slight & the Hibiscus may be sufficiently mature with a dense enough canopy to withstand the freeze with only marginal surface damage which darkens once the thawing is completed.
It is suggested that in minor cases of freeze or frost to leave damaged plant parts on the Hibiscus & this will protect the undamaged inside  parts. (mainly the branches)
Plastic covering is not recommended in the protection of Hibiscus  that are subject to freezing conditions.
The underside of the plastic will condensate moisture & will freeze compounding the problem.
Covering young plants with hession / calico bags or newspaper  is effective in light freeze conditions.
Under very severe cold conditions some Hibiscus fanciers take their containerized hibiscus inside for protection from their local Winters.
When Spring arrives they optionally place them out in the garden free standing in their pots or bury the pot into the ground up to the pot rim & the Hibiscus remain in this position until they are returned  inside again in the Autumn / Fall.
In colder parts of Europe Hibiscus are grown by the millions as small indoor potted colour & are disposed of once they stop flowing & another purchased to replace the previous one.

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 Frost Damage On Hibiscus
Size: X .25
Herbicide Damage
Herbicide Damage to Hibiscus is usually a sign of carelessness in the application of herbicides.
Either spraying on windy days or using the incorrect chemical.
There are two main types of herbicides, selective & non selective
These herbicides are further classified as narrow leaf & broad leaf (monocots & dicots) selective
All these herbicides can be either systemic or contact.
Glyphosate (Round Up) is classified as a non selective, systemic herbicide.
Hibiscus are a broad leaf plant & therefore care must be taken not to over spray them with either non selective systemic or broad leaf selective herbicides.
Non selective contact herbicides are not so dangerous to Hibiscus in low amounts as these herbicides usually just, "Burn Off"  the sprayed parts & are mainly designed for seeding & or annual weeds.
If  you accidentally over spray a hibiscus branch cut off the wetted parts  immediately & this will avoid any damage occurring to the plant.
Carrying a pair of secatures while spraying weeds is good for just this reason.
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Herbicide (2-4D) Damage To
Hibiscus Leaves
Size: X .10

pH
The measurement of pH is indicated by the free Hydrogen Ions within a medium
The extremes range from Acid,  Zero (0) to Alkaline of Fourteen (14)
The ideal pH range of Hibiscus is a slightly acid 6.0 to 6.5
Within  this range the Hibiscus plant is able to access the nutrients at the quantities required for healthy growth.
Below is a graphical chart which indicates the availability of nutrients at different ranges of pH.
The measurements of the readings are indicated by the width if the white line for each nutrient intersecting with the  Ph measurements.
Eg. at the Extremely Acid reading of 4.0 the Element Iron is available at its maximum to the plant & all of the other elements are not so readily available.

To increase the pH of the medium the addition of Calcium in the form of lime will suffice.
Some fertilizers have Calcium as an addition & this is also a way of increasing or stabilizing the pH.

To decrease the pH of the medium the addition of Sulfur in the form of sulfates will suffice.
Some fertilizers have sulfates as an addition & this is also a way if decreasing the the pH.
The addition of organic matter will assist with the acidifying process.

Either way of adjusting the pH always remember, the results of change are not immediate & some weeks to months are required subject to soil temperature & microbial activity to read an accurate & true reading.
 

pH Influence on the Availability of Nutrients To Plants
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 .....Extremely  Acid ......................................................................................................Extremely Alkaline
MAXIMUM NUTRIENT AVAILABILITY IS INDICATED BY THE WIDEST PART OF THE WHITE BARS
 
 

Root Bound
The binding of roots is not as common as once was do to the improvement  of container design which has reduced the likelihood of roots spiraling within the container.
To avoid  the chances of root binding it is better to purchase plants that are not pot bound & to tease out the roots sufficiently to give the older roots a chance to grow & move out into the new soil when planted.
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Pot Bound Roots  Of Hibiscus
Size: X 4.0
Note: Avoid the purchase of containerized Hibiscus that look obviously too big for their container, this may be an indication of  Roots being bound & severe teasing & possible cutting of the roots may be necessary to allow the new roots to develop without choking the plant further.
Variegation
Variegation is not usually a case of concern but a curiosity of sorts.
It is the lack of chlorophyll which gives the appearance of the colour changes.
If a portion of the variegated plants reverts to the normal green colouring there is a strong possibility that it may take over the variegation because of its more vigorous nature.
Variegated Hibiscus are popular for indoor culture where the colour patterns add an extra bonus to the flowers.

A Selection Of Popular  Variegated Hibiscus
Sizes: (Approx.)  X .25

Variegated H. darcyii.
H. Snow Queen..
H. Rose Flake

 

Witches Broom
Also known as Fasciation
This abnormality most commonly involves the flattening of Hibiscus stems, instead of the stem being rounded. It develops into a larger, flatter stem appearing as many stems fused together & is considered to be a mutation.
Daphne, Celery & Celosia are commonly affected.
The removal of the flattened parts usually controls this form of disorder.
 

 Fasciation Of Hibiscus Stems
 
Size:  X  0.5
Yellow Leaves
& Leaf Drop
Hibiscus rosa-sinensis 'cultivars' are classified as an evergreen & as such, normally  do not shed all of their leaves in winter.
There are environmental influences that will cause the shedding of some or most of the mature leaves.
This is termed a natural cycle of the plants development,  where the nutrients are transferred to the growing tips while the old yellow leaves fall to the ground to increase the mulch & the nutrient content of the top soil of which the surface feeding roots of Hibiscus thrive within.
The yellowing of leaves can be triggered by pruning, feeding, sudden change of soil moisture content  & higher than average temperatures & incorrect pesticide chemicals or concentrations.
The total yellowing & loss of all leaves may indicate a root problem (see Root Rot)
 
Yellowing Of Some Mature Leaves of Hibiscus
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 Size: X .10
 
 
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