Caring for Tropical Hibiscus

General Growing Instructions for Hibiscus Rosa-Sinensis

For further growing information consult the informative publication The Hibiscus Handbook or seek the advice of an experienced grower. Both are available through the American Hibiscus Society.

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By following a few general guidelines, one can greatly reduce the rate of disease occurrence and death among hibiscus.

    Every gardener has had the impression, at one time or another, that a particular plant has a "death wish."  But this impression is false. All plants "struggle" to live. And their demise, whenever it does occur, is most often the consequence of neglect, disease or misguided care.

    Planted in the ground, hibiscus tend to give the impression that they are easy to satisfy, and indeed they are. But like any living thing, they do have their tolerances. Disease, insects or neglect can result in the death of a plant, but this is relatively rare. A healthy plant is generally able to "resist" these assaults and recover its vigor. They simply outgrow the problem. The results might not be pretty and the plant will certainly pay a price in beauty and bloom production, but it will generally survive and in time prosper once again.

    Container culture is somewhat trickier, since it is a micro-environment. In pots, hibiscus do not have the ground around them to "buffer" the effects of salts, uneven watering, and pH fluctuations. These problems can be lethal, and when coupled with disease and insects, they frequently are. So, while the same general principles of cultivation apply to both plants in the ground and in containers, hibiscus in containers needed to be monitored more regularly to prevent avoidable losses.  See the page dealing with “hibiscus in pots” on this website.

When buying a hibiscus plant, look for signs of good healthy growth and branching. Since many exotic cultivars are obtained from growers who often raise their plants in protected greenhouses, be cautious about placing plants immediately in direct sunlight. Introduce them to full sun slowly, over a period of 8 to 10 days.
Hibiscus MUST have a well-drained, moisture retentive soil. Even though some cultivars are more tolerant of drainage conditions than others, all tropical hibiscus need a well-drained growing medium.
Most commercial "jungle mixes" and professional potting mixes are fine as long as they drain well and retain moisture without breaking down too quickly. Add some composted hardwood bark if it appears that the soil lacks sufficient porosity. Ideally the potting mixture should be as close to 6.8 as possible and contain a pH buffer.
Hibiscus like "even" watering. Don't let your hibiscus get too dry or stay too wet. If dried out for too long, the plant can drop its leaves or even go into shock and die, despite renewed watering. If overwatered, especially in pots, fungal disease can destroy the root system, or the soil can pack and deprive the roots of needed oxygen. In short, Do NOT water plants if they are still wet.
In summer, when the plants are in active growth, they require more water. While not all cultivars enjoy the same amount of water or tolerate the same amount of dryness, hibiscus in general like being well watered, especially in hot weather. Even so, hibiscus do not like to be continually wet, as this promotes fungal disease and packs the soil, robbing it of vital oxygen. Do not leave them sitting in saucers full of water for too long. If possible, water in the mornings and let the plants dry out over the course of the day.
During cooler periods of the year, water more sparingly. In winter, when the plants are NOT in active growth, water only when the plant is dry. Cool moist conditions are ideal for fungal diseases, and one must be careful NOT to create those conditions.
Occasionally, plants may lose all there leaves. This should not be confused with the plant’s normal replacement of older leaves which is a more gradual process and part of the normal growth process.  A sudden and complete loss of foliage is a reaction to some stress factor in the environment -- too much water or too little water, etc.  Should this happen, correct the imbalance that caused the problem initially.  And remember!  When plants are without leaves, there is relatively little transpiration and it may be days before they need watering again. Overwatering now can cause "root rot."
Fertilize light but often. Hibiscus in active growth are heavy feeders, especially when planted in pots. Some growers fertilize every time they water, in which case they use a diluted, water-soluble fertilizer solution at considerably less than full strength.  Remember too much fertilizer can burn the roots and kill the plant!
Apply fertilizers in the cooler hours of the day, and be sure to water well before applying any granular fertilizer. Be especially careful to keep the plants well-watered after using any granular fertilizer.
The prevailing opinion is that hibiscus do not need (nor want) high amounts of Phosphorus (P, the middle number), but they do demand high quantities of Potassium (K, the last number). Tropical hibiscus fertilizers have ratio numbers like 9-3-13, 10-4-12, and 12-4-18.
Granular fertilizers have the advantage of providing plants with a constant source of nutrients. But some, even those marked hibiscus fertilizer, are prone to burn the roots of the plants, especially if the plant is potted and becomes too dry. Moreover, these fertilizers break down unevenly, depending on temperature. The hotter the temperatures, the faster the granular fertilizer breaks down (despite label assurances). Some growers place a layer of mulch over the granular fertilizer to slow its rate of break down during the hot summer months.
For large hibiscus in the ground, it is easier to keep them consistently fertilized by placing "tree stakes" around the shrub/tree during the early spring. Since fertilizer stakes for hibiscus are not available, I use fertilizer stakes designed for palm trees. I have found that the formulas for palms match very closely those of hibiscus fertilizers.  Do not use these stakes for plants in pots, as they are too concentrated for pot culture and will “overdose” the plant.
Remember: Phosphorus buildup or pH unbalance account for some 95% of the cases of slow decline and eventual death in hibiscus. Phosphorus, the "P" in the N.P.K formula, affects bloom quality and quantity, but hibiscus only need a small amount, since hibiscus "store" phosphorus. Excessive phosphorus will bind up other minerals. The effect can prove toxic to the plant.
Notice buds dropping excessively? "Bud Drop" is a sign of stress. It is occasionally a problem, especially with double-blooming varieties, during excessively hot weather. Some hibiscus cultivars are more sensitive to heat and seem to drop buds almost naturally under these conditions. Hibiscus grow best in daytime temperatures ranging between 75 and 85 degrees Fahrenheit.
Not all "bud drop" is caused by excessive heat. Any stressful condition can prompt the plant to drop its buds. In many cases the cause is one of the following: lack of water, too much water, wind, heavy rain, insects (especially: hibiscus midges or thrips) and/or an unbalanced feeding formula. Check for insects, and if they are not present, try moving the plant into a more shaded area and regulate the watering more closely.
Do not use Malathion liquid to control insects. The oil "carrier" in Malathion will cause the leaves to drop and may even kill the plant. WP (Wettable Power) Malathion is fine.
Some of the new cultivars are grown very successfully in light shade. Potted hibiscus enjoy some protection from our intense, summer sun. A pool/shade screen, providing 25% shade, offers blessed relieve during the hottest part of the summer day and helps prevent stressing the plants, especially those planted in black, plastic pots. Lighter colored pots help prevent the roots from overheating.
Many growers recommend a good layer of compost once a year. If that cannot be done, meet your plants' needs with good soil porosity and an adequate fertilizer formula.
Hibiscus will normally withstand a light freeze. But if the weather is windy, the plant may suffer damage even if temperatures remain as high as 45 degrees Fahrenheit. How much cold a plant can tolerate depends on exposure, wind strength, length of cold, available moisture and slight differences in cultivar tolerances.
Hibiscus need real daylight to bloom. During the winter months, they enjoy full sun all day and will bloom beautifully as long as the temperatures remain mild. A slow down in bloom production and a decrease in blossom size will be noticeable once the evening temperatures drop regularly below 55 degrees Fahrenheit.
Most insect problems (aphids, spider mites) are best handled by spraying underneath the plant's leaves with a hard stream of water at relatively close range.  Two or three sprayings a day for a few days in a row give the best results.  Careful observation and persistence are necessary to keep the insects at bay.
To control severe infestations of mites and/or whitefly, soap sprays are recommended. Use Insecticidal Soap according to the label. Use Palmolive or Dawn or Sunlight soap at one to two tbs. per gallon to smother the insects on the plants. If you need to use more than 2 tbsp/gallon, remember to later rinse off the plant. Spray twice a week until bugs are gone.
There are occasions when chemical sprays seem to be the only way to stop a major infestation. Should you choose to use chemicals, follow directions carefully and use with caution. Although few insecticides injure hibiscus, it is always prudent to check the labels and make sure that the product is recommended for hibiscus.
Spray your plants in the evening after the heat of the day or very early in the morning. This applies to both using insecticides or foliar feeding. There is less danger this way of burning the leaves.
There is no easy "rule of thumb" for deciding when a plant should be repotted. Some growers routinely repot every year; others every other year. However, it is really the plant that decides when to repot. If it becomes lethargic, take a good look at the soil mix. It may have "broken down" and lost porosity.  If this is the case, rework the soil or repot. Should the roots be pressing hard against the pot, it is time to repot.
When repotting, move the plant up to the next size pot rather than putting a small plant into an oversized pot. Instead of potting up, another solution is to prune the roots so that the plant will continue to fit in the original container.  But since the roots have been pruned back and can no longer support the foliage, it is necessary to “balance” the plant by cutting back the top of the plant so that the roots have less plant to support.  This gives them time to recover from the pruning.  Be sure to sterilize the pruning tools (clean with clorox or some anti-fungicide)  before working on another plant, as this will help prevent the spread of disease. Normally, the top of the plant, like the root system, should be cut back by about by about 1/3.   More severe pruning may prove overtax the plant’s ability to recuperate; this is especially true in the case of older, woody plants.   After pruning, the plant can be returned to its original pot.  Place a tablespoon of clorox in a gallon of water and irrigate the newly potted plant well to protect the plant from possible fungal disease.  The next time you water, add some root stimulator to your water, per label instructions.
Plants that have been newly potted up should be watered well, but NOT soaked. Unlike established plants that need thorough watering, newly planted hibiscus need to be encouraged to seek out moisture at the bottom of the pots. Overwatering while a plant is still "filling" in the pot with its root system will encourage root rot and discourage deep root growth. Judicious bottom watering is a good way to avoid this problem.