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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 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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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.

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.
 

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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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.
 

 

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