Ixoras for Year-Round Enjoyment

by

Paula Szilard


Ixoras are ubiquitous landscape plants in tropical areas such as South Florida and Hawaii, rivaling the hibiscus in popularity.  Many are small and medium sized woody shrubs that lend themselves to container culture.  The smaller varieties make excellent indoor plants as long as you can provide a bright location with part sun in a warm sunroom or a heated porch or greenhouse.  They are often called ‘Jungle Geraniums,’ presumably because they bloom almost uninterruptedly, like a geranium.  The only time they do slow down a bit is during the shortest days of winter. Gardeners in cold climates can buy a plant for the patio, enjoy it all summer and bring it in the fall.  It will hardly miss a beat and continue flowering all winter.


Originally found in India, Indonesia, Myanmar, Vietnam, Malaysia and the Philippines, this genus of roughly 300 species and hybrids in the Rubiaceae coffee/gardenia family can range in size from a very small shrub to a small tree.  It has glossy, opposite leaves and large clusters of small, long flowers in red, orange, pink, salmon or white that can last up to eight weeks.  Technically, these inflorescences are called corymbs with 15-50 individual flowers.  To the nonexpert, the just look like the umbels on flowering dill plants or the false umbels on a geranium.


Some of the most commonly available species are Ixora casei, enormous plants which reach 10 feet, and are far too large for indoor or greenhouse culture. Ixora coccinea and Ixora chinensis, on the other hand are much smaller.  Coccinea is a small shrub growing up to 4 ft tall.  It is even smaller when grown in a container, of course.  As its name would indicate, it has orange red flower clusters.  Ixora chinensis is a larger shrub, about 6’ tall and 3-6’ wide.  The cultivar ‘Maui’ has striking orange red clusters of flowers.  The smallest ixora cultivar, referred to as Ixora taiwanensis is often described as a dwarf.  It maxes out at 2 feet when ground in the ground, making it eminently suitable for indoor culture. There are cultivars available in many different colors.


Ixoras have some specific requirements for cultivation.  They require acidic soil.  Some of the usual peat-based mixes may not be acidic enough, so experts suggest adding leaf mold to further acidify the mix.  It might be worthwhile checking on the maunfacturer’s website for the pH of your mix. If ixoras don’t get soil of a pH of 5 to 5.5, they have difficulty absorbing certain nutrients, such as iron and manganese.   They will suffer from iron chlorosis, evidenced by interveinal yellowing on newer leaves.  This condition cannot be remedied by the application of extra iron to the soil.  It can only be remedied by foliar sprays of iron, which permanently stain concrete, so be careful where you do this.  In any case, unlike the soil in your garden, the pH of container plant mixes is under your control, and chances are you will never have to do this if you use a suitable mix.


Ixoras also require good drainage, which is facilitated by the addition of some gritty sand to the mix.  At the same time, they prefer potting mix that’s on the moist side.  In the winter months the recommendation is to water more sparingly because the plants are exposed to less sun and therefore transpire less water into the air around them.  Keeping ixoras in a warm environment is critical. They don’t thrive in temperatures below 60 F.  Experts also recommend that you do not allow the soil temperature to dip below this number.  Finally, ixoras love lots of humidity.  Unless you have a sizable collection of indoor plants that fill the air with moisture, you may have to resort to a humidifier.  Fertilizing is geared to growth patterns.  During the most active growth period, from spring through summer, plants should be fertilized once a week.  In the fall and winter, reduce fertilizing to once a month.  One suitable formulation has an NPK ratio of 4-8-8.  This means it has 4 parts nitrogen to 8 parts phosphorus and 8 parts of potassium.   Another option is to alternate an all purpose fertilizer, such as 20-20-20 with one specifically geared to support bloom production.


Since ixoras are shrubs, pruning will be a necessary, if infrequent task in their care. Because people in tropical areas grow them as hedges, we know that shearing them reduces flowering.  As with most shrubs, an annual pruning is desirable.  Spring is the best time for this because plants begin to send out new growth.  When pruning, do not continually cut off the tips of plants.  This has the same effect as shearing and removes emerging buds and results in less flowering.


These beautiful plants do have a downside.  They need to be monitored for aphids, scale and mealybugs.  Experts from the University of Florida recommend a light horticultural oil mixed with water according to directions at the first sign of these pests.  The aphids and the mealybugs secrete a sticky honeydew, which adheres to the leaves and provides the perfect environment for the growth of a fungus called sooty mold, which inhibits photosynthesis by covering the leaves.  Fortunately, it can be washed off by a strong spray of water or with soapy water and a soft cloth. 


Sources consulted:

Flowering Tropical Plants

Keeler, Gail and Rick Schoellhorn.  Ixora for South Florida  Gainesville, FL: University of Florida IFAS Extension (ENH 955)


2003. Gilman, Edward F.  Ixora coccinea.  Gainesville, FL:  University of Florida, Cooperative Extension, Oct 1999, (Fact Sheet FPS-291)