A genus of flowering plants from the Rubiaceae (coffee) family, Gardenia species are highly praised for their exquisite creamy-white, fragrant flowers and attractive dark-green foliage.
While they are not easy to grow and known as finicky plants with particular growing requirements and high susceptibility to diseases, their beautiful flowers and glossy foliage make up for the extra attention they need.
Whether cultivated in the ground or a pot, gardenias need the right care and regular maintenance to flourish.
And this includes feeding the plants with the right kind of fertilizer at the right times.
Fertilizing is essential for gardenias to ensure healthy growth and vigorous flowering.
- Best Fertilizer for Gardenia Care
- When or How to Fertilize Gardenia Species
- Signs of Lack of Fertilizer
- Mature Height/Spread
- Growth Rate
- Landscape Use
- How to: grow gorgeous gardenias
- How to Grow Gardenias
- Fertilize Your Gardenias
- Success with Gardenias
Best Fertilizer for Gardenia Care
The members of this genus including the ground cover Gardenia varieties are acid-loving plants. Hence, they will not benefit from an all-purpose fertilizer.
While you are allowed to use liquid, pellet, or powder fertilizer, make sure it has higher acidic content.
Use the ones specifically meant for acid-loving plants (Azaleas, Camellia, Rhododendron) or supplement with materials, like Epsom salt, tea, or coffee grounds to make it more acidic.
Fertilizers containing additional copper or iron also promote the development of leaves and flowers.
Here are some popular and widely used commercial fertilizers for gardenia plants you’ll find at the garden center:
- Scotts Miracle Grow MirAcid
- Fox farm Grow Big
When or How to Fertilize Gardenia Species
As discussed above, fertilization is one of the most important elements of caring for gardenia plants.
While fertilization is essential to maintain a consistent supply of nutrients essential for healthy growth and blooming, too much fertilization will burn the plants.
To prevent over-fertilizing, experts recommend to only feed the plant once a month through early spring, early summer, and late summer.
Do not fertilize gardenia bush in fall and winter, when they are dormant (you may fertilize in early fall though when they are not dormant).
Another tip to avoid over-fertilizing is to use lesser amount than what is recommended on the packaging.
Depending on the type of fertilizer you are using, apply it diluted in water (liquid fertilizer) or mix directly into the soil (powder or granular fertilizer).
Mix one tablespoon of white vinegar in a gallon of water and water gardenia plants with it once a month helps to maintain the acidic soil pH.
Important: Always water the plant, only lightly though, before fertilizing.
Applying gardenia fertilizer when the soil is completely dry may damage the roots.
Signs of Lack of Fertilizer
In an attempt to prevent over-fertilizing, sometimes people end up under fertilizing the gardenia plants, which affects the plant in many ways.
If your gardenia jasminoides are exhibiting any of the following signs, it means you are not fertilizing them enough:
Stunted New Growth
A lack of nitrogen inhibits new growth.
If any of this evergreen shrub isn’t producing new growth, it is a sign of lack of this essential nutrient due to under-fertilizing.
The plant grows best in USDA hardy zones 8 – 11.
These house plants are vulnerable to pests such as aphids, mealybugs, whiteflies, and mites when grown indoors, so they should be monitored daily, watch out for sooty mold, and infestations treated immediately.
Use a horticultural oil or insecticidal soap to control these pests.
Leaf development, again, is highly dependent on the amount of nitrogen gardenia plants are getting from the soil.
When they do not get an adequate amount of nitrogen, then the green leaves start to turn yellow.
More on Yellowing Leaves on Gardenia Plants
And the lack of healthy leaves means the plant’s ability to perform photosynthesis will be reduced, as a result of which they won’t be able to make enough food.
Yellow, curled leaves with green veins is a sign of iron deficiency.
Prune away dead areas.
All these factors contribute to poor health and reduced growth and blooming.
Absence of Flower Buds or Flowers
The lack of nutrients in the soil makes the plants go into survival mode, during which it only uses, whatever nutrients are available, to fulfill its essential survival needs, such as the development of roots and causes bud drops.
To sum up, the lack of essential nutrients and organic matter significantly affects the health and growth of gardenia plants.
Use mulch, peat moss, and avoid extended periods of full sun to keep it healthy.
Feeding with the right fertilizers will help encourage foliage and flower development, once again, by restoring the nutrient balance of the soil.
Gardenias have been popular shrubs in South Carolina since the 18th Century and have been grown by the Chinese for over a thousand years. They were named after the Scottish naturalist Alexander Garden (1730 – 1791). Gardenias are not the easiest shrubs to grow, but the exquisite white, fragrant flowers make up for the extra attention gardenias require.
Double-flowered gardenia (Gardenia jasminoides) blossom.
Karen Russ, ©2008 HGIC, Clemson Extension
Gardenia (Gardenia jasminoides) is also known as cape jasmine and is an evergreen shrub that typically grows to a height of 3 to 8 feet, depending upon the cultivar. Spread is usually about the same as the height. The foliage of well-fed shrubs is glossy, dark-green, 2- to 4-inches long and half as wide. Depending on the cultivar, the flowers can be either single or double and from 2- to 4-inches in diameter. They are waxy, white, and very fragrant.
The growth rate is medium.
Gardenias are primarily grown for their fragrant flowers and handsome foliage. They should be planted where people will notice the fragrance. The flowers open over a long period of time, from May through June, and sporadically throughout the summer. Gardenias are considered deer resistant shrubs.
Single flowered gardenia blossom (Gardenia jasminoides).
Flickr: Creative Commons License 2.0
Gardenias require considerable maintenance. Fall is the best time for planting. They are best planted in light to partial shade, preferably with morning sun and afternoon shade. Gardenias resent root disturbance. Smaller cultivars will also grow well in containers and placed where their fragrance can be enjoyed.
Gardenias prefer acid (with a pH of less than 6.0), moist, well-drained soils. Add organic matter, such as compost or ground composted pine bark, to the planting bed and till into the soil before planting. Mulch plants with a 2- to 3-inch deep layer of pine straw, compost or ground bark.
Fertilize gardenias lightly in the spring once frost has passed with a well-balanced, extended-release, acid-forming, azalea fertilizer. Fertilize the shrubs again 6 weeks later to encourage extra flowers or faster growth of young shrubs. By well-balanced, this means to look for nutrients in the ratio of 2-1-1. Fertilizer examples are:
Complete, acid-forming organic fertilizers are also excellent choices for use on gardenias for spring and early summer fertilization. They are typically not as nutrient rich, and because of both the low nitrogen content and their inability to burn the roots, they can be mixed lightly into the soil in the fall at planting to enhance root growth. Organic fertilizer examples are:
Do not fertilize gardenias in the fall. Doing so will stimulate tender growth, which may be killed if the temperature in winter drops below 15 degrees. Gardenias are cold-sensitive and during severe winters can be killed to the ground in the Upstate. Often they regenerate in spring.
Additional products containing iron may be applied during the growing season, if needed to correct the yellowed new foliage caused by an iron deficiency. This may occur if gardenias are limed or are planted near a new concrete foundation. An example of an iron-supplement is Southern Ag Essential Minor Elements, which contains not only iron, but also numerous trace elements.
Gardenia “hips” are the fruit that occasionally appear in fall (Gardenia jasminoides).
Karen Russ, ©2008 HGIC, Clemson Extension
Prune shrubs after they have finished flowering in summer to remove straggly branches and faded flowers. Gardenias should be watered weekly during periods of drought in summer. Drip-irrigating the shrubs will keep water off the foliage and blossoms and prevents leaf spots.
Most of the older gardenia cultivars are cold hardy to USDA zone 8, but many of the newer and smaller cultivars are hardy to at least USDA zone 7a. Dwarf cultivars, however, are often more cold sensitive.
A whitefly infestation is the most commonly occurring problem on gardenias anywhere in the state. Whiteflies have piercing-sucking mouthparts, with which they penetrate the cells of a leaf, and then suck out the leaf sap. The top sides of infested leaves may become pale or spotted. These small, white-colored flies often remain unnoticed, as they primarily infest the lower surface of each leaf. As this pest removes plant sap, it excretes a large amount of clear, colorless, sugary waste, which drips onto the leaves below. This sugary waste, called honeydew, is quickly colonized by a black mold (sooty mold), which coats the leaves in summer.
Whiteflies can be controlled by sprays to the lower surfaces of leaves with an insecticidal soap solution or a horticultural oil. Both of these less toxic insecticides kill by suffocation. Sprays may need to be repeated every few days until the whitefly population is under control. Follow label directions for mixing an insecticidal soap spray. Use horticultural oils as sprays between the temperatures of 45 and 90 degrees, and spray in the early morning or late evening to slow the drying time of spray. For horticultural oil, mix and spray a 2% solution (5 tablespoons of oil per gallon of water). See Table 1 for examples of brands and products.
Dark-colored sooty mold will grow on the sticky honeydew, which drips from whiteflies when feeding on gardenia foliage.
Joey Williamson, ©2015 HGIC, Clemson Extension
Alternatively, numerous synthetic pyrethroid contact insecticides (such as bifenthrin, Cyfluthrin, and lambda cyhalothrin) will also control whiteflies if sprayed on the lower surfaces of leaves. Acephate, however, is a foliar systemic insecticide that will move through the leaf tissue. So, sprays to the upper leaf surfaces will move downward to control the whiteflies. All foliar sprays may need to be repeated once or twice at 10 day intervals, as they typically do not kill the eggs. Do not spray plants in bloom to prevent injury to pollinating insects. See Table 1 for examples of brands and products.
Instead of numerous insecticidal sprays, a single soil drench of imidacloprid can be applied at the base of the shrubs in the spring as new growth appears to give season long control. Follow label directions for mixing and application. See Table 1 for examples of brands and products.
Similar in habit are small gray aphids, which cling to leaf undersides. These can be easily controlled with insecticidal soap sprays. Nematodes are microscopic worms, which live in the soil and feed on plant roots. In sandy soil, these plant parasitic nematodes can cause gardenias to become stunted or even die. Root rots caused by several different fungi can also be a problem, primarily in poorly drained soils.
Although much less common, another problem encountered is “bud drop.” Flower buds may abort and drop off just before they open. Causes of bud drop include low humidity, overwatering, under-watering, insufficient light and high temperatures (night temperatures between 50 and 55 °F are necessary for the formation of flower buds).
Larger, Upright, Double-flowered Cultivars:
- ‘August Beauty’ grows 4 to 6 feet high and 3 to 4 feet wide. Blooms heavily from mid-spring to fall with double 3-ich flowers.
- ‘Mystery’ is the best-known selection. It has 4- to 5-inch, double white flowers and typically grows 4 to 6 feet tall and 3 to 4 feet wide, but may get larger.
- First Love® (‘Aimee’): May be listed as ‘Aimee Yoshida’. Very large (4 to 5-inch in diameter), double blooms. Plants are larger than ‘August Beauty’. Grows to 5 to 8 feet tall and 3 to 6 feet wide.
- ‘Frost Proof’: This cultivar produces 2- to 3-inch, double, fragrant blooms during early summer and sporadically during the remainder of the summer. It grows to 5 feet tall and 4 feet wide. It is more tolerant of early spring frosts.
- ‘Mystery’: This older cultivar grows to 5 feet tall and 3 feet wide, but may reach 6 to 8 feet tall. It produces very large, double flowers.
- Summer Snow® (PP22797): This cultivar grows to 4 to 5 feet tall and wide with double flowers, and is a very cold hardy cultivar.
- ‘Veitchii’: This is one of the oldest cultivars and grows to 4 to 6 feet tall and 3 to 4 feet wide. It has double flowers with a long bloom period.
Smaller Cultivars with Repeat Blooming:
- ‘Chuck Hayes’: This is an extra cold hardy cultivar that grows to 4 feet high with semi-double, 2 to 3-inch flowers during summer, and has a profuse re-bloom in fall.
- Crown Jewell® (PP19896): A cross between ‘Kleim’s Hardy’ and ‘Chuck Hayes’ gardenias. It has a heavy bloom set with double, fragrant flowers, and very good cold hardiness. Blooms on old and new wood. Prune lightly after flowering to stimulate more flowers to form. This cultivar has a spreading habit, and grows to 2 feet tall and 4 feet wide.
- ‘Daisy’ is a more cold hardy variety recommended for the Upstate of South Carolina. It grows to about 3 feet tall and wide, and produces single-flowered blooms.
- ‘Double Mint’ (PPAF): From Plant Introductions. These compact, dense shrubs grow to 3 feet tall and wide, and produce double, 2-inch blooms. Flowers in early summer and repeat blooms throughout the summer.
- Heaven Scent® (‘Madga I’, PP19988): From the Gardener’s Confidence® Collection. It is a hybrid of G. taitensis (Tahitian gardenia) and G. jasminoides. This repeat bloomer grows to 3 to 4 feet tall and wide with fragrant, semi-double, 5- to 6-inch flowers. Has a tight, compact form.
- Jubilation™ (‘Lee One’, PP21983): From the Southern Living Plant Collection. This cultivar grows to 3 to 4 feet tall and 3 feet wide. It blooms with double flowers in late spring and re-blooms during summer into fall.
- ‘Kleim’s Hardy’ is hardy to 10 °F and grows to 3 feet tall and wide with single flowers in summer. It blooms in May and often has a smaller flush of blooms in fall.
- Pinwheel® (‘PIIGA-1’, PP22510): Blooms in late spring and repeat blooms until fall with fragrant, narrow-petaled, single flowers. Grows to 4 feet tall and wide.
- Scent Amazing™ (‘LeeTwo’, PPIP): From the Southern Living Plant Collection. This cultivar grows to 3½ feet tall and 4 feet wide. It has single white blossoms and blooms late spring/early summer, and then repeat blooms through fall.
- ‘Variegata’: This cultivar has nicely variegated foliage and double flowers on a compact, 3 to 4 foot tall and wide plant.
- ‘Fragrant Pathways’: This is an evergreen groundcover that grows from 8- to 10-inches high with a 3 foot spread. White double flowers and narrow foliage on this dwarf.
- ‘Radicans’ grows to only 6 to 12 inches tall and spreads 2 to 3 feet, with small, dark green leaves and inch-wide double flowers in summer. It is not very cold hardy.
- ‘White Gem’: This dwarf cultivar grows slowly to 2 feet tall and 1 to 2 feet wide. It produces single, 6-petaled flowers in late spring/early summer, and makes an excellent container plant.
Table 1. Pesticides to Control Insect Pests of Gardenias.
|Active Ingredients||Examples of Brands & Products|
|Acephate||Bonide Systemic Insect Control Concentrate|
|Bifenthrin||Ferti-lome Broad Spectrum Insecticide Concentrate; & RTS
Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate; & RTS
Up-Star Gold Insecticide Concentrate
Bifen I/T Concentrate
Talstar P Concentrate
|Cyfluthrin||Bayer Advanced Vegetable & Garden Insect Spray Concentrate; & RTS|
|Horticultural Oil||Ferti-lome Horticultural Oil Spray Concentrate; & RTS
Southern Ag Parafine Horticultural Oil
Bonide All Seasons Spray Oil
Monterey Horticultural Oil Concentrate
Summit Year Round Spray Oil Concentrate
|Imidacloprid||Bayer BioAdvanced Garden 12 Month Tree & Shrub Insect Control Concentrate
Bayer BioAdvanced 12 Month Tree & Shrub Insect Control Protect & Feed (2-1-1)
Bonide Annual Tree & Shrub Insect Control with Systemaxx
Ferti-lome Tree & Shrub Systemic Insect Drench
Ferti-lome Tree & Shrub Systemic Insect Granules
Monterey Once A Year Insect Control II
Bonide Systemic Insect Spray with Systemaxx RTS
Ferti-lome Systemic Insect Spray Concentrate; & RTS
Hi-Yield Systemic Insect Spray Concentrate; & RTS
Merit 2 Granular
Martin’s Dominion Tree & Shrub
|Insecticidal Soap||Bonide Insecticidal Soap Concentrate
Espoma Earth-tone Insecticidal Soap Concentrate
Natural Guard Insecticidal Soap Concentrate
Garden Safe Insecticidal Soap Insect Killer Concentrate
Safer Brand Insect Killing Soap Concentrate
|Lambda Cyhalothrin||Spectracide Triazicide Insect Killer for Lawns & Landscapes Concentrate; & RTS|
|RTS = Ready to Spray (a hose-end spray bottle)|
How to: grow gorgeous gardenias
The best way to maintain bushy growth is to prune the flowers with a 10-15cm stem – perfect for a vase. If the shrub has been neglected and become straggly now is the time for a renovation prune. Remove up to 60 per cent of the shrub, leaving a few leaves on the lower third of the bush to aid recovery. Remove any weeds or grass from around the base of the plant and fertilise as above, then drench the plant in seaweed solution.
Yellow leaves will be avoided if you follow the feeding program outlined here. To deal will aphids, brown and white wax scale, hibiscus beetles and caterpillars, keep a close eye out and spray every month with EcoOil. This will also prevent the black sooty mould that follows an infestation of aphids or scale.
Photo – Linda Ross
G. augusta ‘Florida’ is a glossy-leaved evergreen shrub to 1.5m high, with heavily perfumed flowers in flushes from spring to autumn. Good as a hedge.
G. augusta ‘Magnifica’ has larger flowers than ‘Florida’ but flowers just the once.
G. augusta ‘Radicans’ is a low-ish ground cover with smaller leaves and flowers.
G. augusta ‘Aimee Yoshiba’ has a similar growth habit to ‘Florida’, with larger flowers, and larger, more open foliage.
Text: Linda Ross
How to Grow Gardenias
Gardenia shrubs are prized by gardeners for their highly fragrant flowers and bright, glossy, evergreen foliage that’s attractive year-round. When given the right growing conditions, these heat-loving shrubs will thrive. Choose the right place to plant a gardenia and give it the specific care that it needs, and you’ll be rewarded with romance and beauty.
Selecting the right variety
While all gardenias sport fragrant flowers, there are marked differences from variety to variety in mature size and bloom time. First decide what role your gardenia will play in the landscape. Will it be a centerpiece of a border or line a foundation with plenty of room to stretch out? Do you need a tidy, low, flowering border along a walkway or edging a bed? Are you trying to fill a large pot that will sit on a deck or patio? There is a gardenia variety to suit just about every landscape design need from compact smaller varieties that mature to 4 feet tall (such as Everblooming Gardenia) and others that top out at 8 feet tall and wide (such as First Love® Gardenia). Also, take into account blooms and bloom time. Some gardenias offer fewer but super-large 4-in diameter blossoms or while others have smaller, but more abundant flowers. By planting several gardenias with different bloom times it’s possible to have a sequence of flowers from May through August.
- Zone: Gardenias are subtropical plants that thrive in warm, humid weather. Most gardenias are hardy in zones 8-11, though a few varieties hardy to zone 7 have been developed (Kleim’s Hardy gardenia is one), and a few are only hardy in zones 10 and 11 (including Double Tahitian gardenia).
- Soil: Gardenias require a soil pH of between 5.0 and 6.5, which is considered acidic to slightly acidic. It’s wise to take a soil test with a simple kit available at nurseries and home-improvement centers. If the soil pH is too high, amend with sulfur, which is available in a variety of chemical forms. If possible, amend the pH up to six months or a year before planting to allow the application to work. In addition to the right pH, the best soil for gardenias will be a lightweight and full of organic matter with good moisture-retention properties. If your soil is heavy and clay, or very sandy, amend with copious amounts of compost. If planting gardenias along a house’s foundation, test the pH; soil around the foundation can have a much different pH than soil in the center of the garden.
- Moisture: Constant moisture is non-negotiable for gardenias. They’re not drought-tolerant, but they also don’t want soggy roots. It’s essential that you site them in an area with well-drained soil. Organic matter helps retain moisture at the level the shrubs need. Too much clay can lead to waterlogged soil while overly sandy soils dry out quickly and don’t retain nutrients.
- Light: Gardenias can handle full sun, but need protection from baking midday or afternoon sun in higher growing zones. North and east-facing exposures are ideal because they will receive bright morning light and some midday light, but won’t be in full sun all day or during the absolute heat of the day.
The best times for planting are fall and spring when temperatures are moderate. If growing in a colder zone, plant in the spring so that plants can root in well before the fall. Gardenias, much like camellias, like to be planted a little high. Dig a hole that is twice as wide and just as deep as the plant’s rootball. Firmly pack 3-4 inches of soil at the bottom of the hole and place the plant in it. Backfill with the same soil that you removed from the planting hole—do not mix compost in. Finish by mulching with compost, taking care not to mound it around the stem. Renew this mulch layer every fall to protect the plants during the winter and spring to control weeds.. Avoid cultivating around the root zone of gardenias once they are established. They do not like to be disturbed. It’s better to hand-pull weeds or mulch.
Gardenias grow best when they receive at least one inch of water per week. If your area is not receiving that in steady rainfall, water deeply once a week.
Check the pH to make sure it’s in the desired range of 5.0-6.5 before fertilizing. Apply a slow-release fertilizer formulated for acid-loving plants in the mid spring and mid summer.
Prune gardenias to maintain size in the summer after they finish blooming and throughout the year to remove dead or diseased growth as necessary. You can prune the shrubs hard after blooming, but they may not flower as profusely the next year. Gardenias, used as a hedge, will tolerate shearing, but you’ll risk sacrificing blooms and encouraging dense growth that serves as a home for fungal diseases to thrive. There are better plants to use for a formal hedge. (They’re great for informal hedges, though.)
- Sooty mold: Sooty mold is a gray, fuzzy mold that covers the plant leaves and is a symptom of a whitefly or aphid infestation. Rid plants of those pests using insecticidal soap and mold will recede.
- Bud drop: Lack of adequate water during the summer can cause bud to drop so it’s important to always irrigate during dry weather. Lack of sunlight can also lead to bud drop or even cause the plants not to form flowers. Finally, insect problems from aphids or whiteflies can cause bud drop. Eliminate issues one by one, and you’ll have a gardenia covered in blooms.
- Yellowing leaves: Root rot can lead to yellowing leaves. Try to pull the plant up. If it come s out of the ground easily and the roots are mushy, root rot is the culprit and the plant should be discarded. Iron chlorosis (iron deficiency) causes yellow leaves; adjust the soil pH and, possibly, apply a foliar feed of iron.
- Failure to set flower buds: Usually when a gardenia flat out won’t produce flower buds it is growing in too much shade. Move it where it will get more sunlight. Sometimes an aggressive late summer pruning will interfere with flowering as well.
Growing Gardenias Indoors
Gardenias are not indoor plants, despite the fact that they are often sold in the florist trade as such. Two limiting factors to indoor gardenia health are light and humidity. It is almost impossible, without a greenhouse or sunroom, to get the plants enough sunlight for them to set and retain flower buds. Sometimes indoor gardenias will grow flower buds, but the buds will drop before opening. Placing the plant in a south-facing window that protrudes slightly so that sunlight reaches the plants on three sides will give you the best chance of success. To elevate humidity, use a humidifier placed near the plants in the room where the plants are growing. Misting the leaves is a temporary relief, and can encourage spread of fungal diseases.
Eight years ago, I planted several ‘Mystery’ gardenias. Today they are flourishing and will be covered with flowers all summer long.
But I take no credit for their success. For most of their eight years, they did not flower much. Yet, as I have learned with the passage of time, plants are a lot like children. If you can manage to keep them alive for a sufficient number of years, they will eventually find their own way.
Part of my gardenias’ eventual success, I have come to understand, is linked to the growth of the plants around them.
Gardenias appreciate elevated humidity in the surrounding air and this is achieved, in my case, by the growth of volunteer crape myrtle (Lagerstoremia indica) and pride of Madeira (Echium candidum) seedlings close by. With the foliage of these and other bushy plants transpiring around the gardenia, there is more moisture in the air with each passing summer. Although my gardenias face west, the afternoon sun is blunted by the shading presence of my gardenias’ companion plants.
Gardenias are definitely not shade-loving plants and do best growing in either full morning sun or partial afternoon sun. The healthiest gardenias I ever saw were growing on the east side of a car wash in Van Nuys. A steady mist coming from the car wash provided the ideal atmospheric ambience for the gardenias luxuriating there.
Gardenias are among the most puzzling plants for Valleyites to grow. Of every 10 gardenias I see in local gardens, at least nine look sad. Leaves are yellow or burnt, growth is spindly, and the plant as a whole looks ready for the compost heap.
Whenever I have trouble growing a plant, I learn about its habitat. If I can get to know its natural environment, I can attempt to duplicate that environment in my own garden.
Gardenias, indigenous to southeastern China, Africa and Oceania, are used to soil that is acidic due to heavy rainfall that leaches alkaline compounds out of the soil.
Hmm … acidic soil is the exact opposite of the alkaline soil found throughout the Valley. What’s a gardener to do?
You can acidify Valley soil by adding peat moss or gypsum to it during planting, by using fertilizer that is formulated specifically for acid-loving plants and by continual applications of compost. The breakdown of compost, in releasing humic acid, has an acidifying effect on the soil. Gypsum can also be applied twice a year after planting.
Regardless of the pH, your soil must be very fast-draining if gardenias are to have a fair chance of feeling comfortable in it. If your soil is compacted, mix in topsoil — sold in nurseries by the bag — whose primary constituent is sand. Adding compost also will improve soil drainage.
Root protection is a key factor in gardenia health. Like many tropical plants, gardenias grow best with their heads in the sun and their feet in the shade.
If your gardenia is a ‘Veitchii’ (VETCH-ee-eye), its growth habit is bushy and it will shade its roots completely as it develops. If your gardenia is a ‘Mystery,’ its growth will be more vertical and you will want to surround it with mulch and/or other plants.
If your gardenia is growing in a container, place a variety of tougher potted plants, such as geraniums and succulents, around it for protection from hot sun which, striking the sides of your gardenia’s container, would stress its roots on hot days.
With a gardenia, the only pruning required is removal of dead stems and trimming back shoots that go outside the natural shape of the plant. Gardenias should be allowed to reach their mature dimensions, 5 feet tall and 6 feet wide for ‘Veitchii,’ 8 feet tall and 8 feet wide for ‘Mystery.’
Gardenias prefer soil that is consistently moist but never overly wet and never dry. In summer, gardenias growing in the ground should be soaked every three days. In containers, they may need more frequent watering, depending on the container’s size and location. From March to November, apply a fertilizer for acid-loving plants, together with iron chelate, once a month.
Having said all that, I have seen gardenias that appeared to thrive on neglect. Once, in Valley Glen, I was introduced to a ‘Mystery’ gardenia that was 20 years old, had never been fertilized and flowered nonstop for months. It faced east and received a significant dose of morning sun.
I also am familiar with a ‘Veitchii’ gardenia in Sherman Oaks that is wedged against a fence in a side yard next to a concrete walkway. It is watered once a week, is never fertilized and keeps close company with a billowy, vining star jasmine (Trachelospermum jasminoides). It gets a few hours of sun each morning and is covered with flowers throughout the summer. It would appear that just as in real estate, location — or microclimate, horticulturally speaking — means everything to gardenias.
The history of the gardenia is intertwined with the first years of the American republic.
Alexander Garden grew up in Aberdeen, Scotland, where he studied medicine and natural history before voyaging to Charleston, S.C., where he took up residence in 1752. In addition to his medical practice, Garden became an avid plantsman and sent local specimens he discovered back to Europe.
It was during this period that the Swedish botanist Carolus Linnaeus began to give genus-species names, in Latin, to plants and animals, a system that would become known as binomial nomenclature. When Linnaeus received a plant from China with flowers that smelled like jasmine, he was persuaded to name it after Alexander Garden (Gardenia jasminoides) for his work in bringing wider recognition to newly discovered American plants.
Linnaeus sent a sample of the sweet-smelling newly named Gardenia shrub to Garden, who promptly planted it in his garden where, serendipitously, the Carolinas’ semitropical climate and acidic soil provided the perfect conditions for the first gardenia ever grown on the American continent.
Incidentally, a single gardenia bloom floating in a shallow glass bowl makes a pleasingly aromatic, stand-alone subject for a modest tablescape.
Tip of the week
For the Fourth of July my wife baked an apple pie whose fruit came from a ‘Golden Dorsett’ tree. ‘Golden Dorsett’ is the sweetest, most “appley” tasting yellow apple you can find. The tree was planted five years ago and hardly fruited at all until now. As in the case of ‘Mystery’ gardenia, ‘Golden Dorsett’ apple teaches the virtue of patience in the garden.
Joshua Siskin’s column appears every Saturday in this section. He welcomes questions from readers and will answer them in his column. If you have a question, please send an email to [email protected] Include your full name and the city you live in.
Fertilizer provides gardenias with important nutrients to boost plant growth and flowering. However, it takes the right kind of fertilizer applied at the proper time to get the job done.
Fertilize Your Gardenias
Gardenias love acid-rich soils, and the soil pH should be between 5 and 6, with an ideal of 5.5. Before applying fertilizer, have the soil pH tested. If the pH is higher and on the alkaline side, or above 7, a soil acidifier helps bring it back to the level gardenias love.
Signs that your gardenia plant may need fertilizer include:
- Yellow leaves: Leaf development depends on nitrogen, and a lack of available nitrogen within the soil may contribute to yellow leaves. Without healthy leaves, plants cannot make their food through photosynthesis.
- New growth stunted: This is another sign the plant needs more nitrogen to support growth.
- No buds or flowers: When nutrients in the soil are scarce, plants enter survival mode, focusing on basic survival needs like root development. Fertilizing gardenias restores this balance and encourages flower development again.
When to Fertilize Gardenias
Gardenias need fertilizer during their growth cycle to support development and fuel growth and flowering. Flowering is part of the reproductive cycle of plants. Plants expend a great deal of energy creating baby plants! Fueling growth by fertilizing gardenias adds valuable nutrients back into the soil which are used during blooming cycles.
- Prime time for fertilizing gardenias is April through November for the vast majority of gardeners.
- Gardeners in southern Florida and similar garden zones should fertilize anytime between March and October.
- Space the application of fertilizer out in two to four week intervals. It is better to err on the side of caution and fertilize less frequently than more frequently, because too much fertilizer can burn the gardenia’s roots.
What to Use
Since gardenias are acid-loving plants, you will need a fertilizer created especially for gardenias and similar plants.
Scotts Miracle Grow MirAcid is perhaps the most popular brand of fertilizer for gardenias. MirAcid contains a ratio balance of 30-10-10. These numbers represent the ratio of nitrogen (N), phosphorus (P) and potassium (K) contained in the mix. MirAcid also includes copper, manganese and other trace elements, which are great for leaf and flower development. MirAcid fertilizer contains inorganic chemicals, so if organic gardening techniques are important to you, you may want to try one of the many organic fertilizers on the market.
Fox Farm Grow Big fertilizer contains a balance of 6-4-4, and it’s readily available online or in your local garden center. It provides a steady, slow release of organic materials into the soil with an emphasis on nitrogen.
Yum Yum Mix is another organic fertilizer which contains a ratio of 2-1-1. Created by Sante Fe landscape design expert Donna Bronner, Yum Yum Mix is especially good for nutrient-poor alkaline soils, such as those found in and around New Mexico and other southwestern states. It includes a rich blend of alfalfa meal, cottonseed meal, rock phosphate and other goodies that not only provide plants with nutrients, they also nurture beneficial soil microorganisms.
How to Fertilize Gardenias
In general, gardenia fertilizers come as powders, pellets or liquids. They’re typically mixed with water in a ratio listed on the package direction. Depending on the fertilizer you’ve chosen, you’ll either mix the fertilizer directly into the soil or water it into the soil around the plant.
Avoid sprinkling fertilizer on the leaves because it may disfigure them. A common mistake among neophyte gardeners is to sprinkle water or fertilizer on the leaves, instead of the soil, in the mistaken belief that the leaves take up nutrients. It’s the gardenia’s roots that need the nutrients, so be sure to get as much as you can into the soil.
Apply pellet fertilizers by mixing gently into the soil around the plant in the recommended amount. Powders and liquid concentrates typically require mixing with water before applying to the soil.
Success with Gardenias
Gardenias may not be the easiest plants you can grow, but they are certainly worth the effort once you smell those heavenly flowers. Always read and follow the package directions carefully for whichever fertilize your use, and your gardenias will thank you with an abundance of blossoms.