The fragrance of gardenias, an illusive mix of vanilla, jasmine and nutmeg, is well known to most gardeners. The unmistakable scent floods a persons senses so thoroughly that, once smelled, it is forever remembered.
Originating in China, where it was grown and admired for over a thousand years, gardenias were first described by botanists in 1761. “Gardenia” was chosen as the name for this fragrant group of plants not on behalf of a garden, but in honor of Dr. Alexander Garden, a well-known naturalist living in the Carolina’s at the time. Although named to honor a great naturalist, it is in our gardens where has gained its fame.
Some plants just perform better in the coastal gardens of Orange County than they do inland. Gardenias are one of these. But even in our nearly perfect coastal climate, gardenias struggle in some gardens while thriving in others. If the climate of our Newport/Costa Mesa area is ideal for gardenias, why the discrepancy of the many gardenias planted in our gardens?
The basic needs of gardenias in coastal Orange County are rich organic soil, quick drainage, even and consistent soil moisture, especially during summer, at least a half-day of direct sunlight and a soil pH of between 5.0 and 6.5. All of these can be achieved with a bit of planning, the proper location in the garden and the use of acidic soil amendments and fertilizers.
Coastal gardeners struggling to grow and flower gardenias usually complain of one of two issues; either the buds are dropping prematurely, or the plants are pale, woody, thin and sickly looking.
The causes of buds turning brown and dropping before opening is usually caused by poorly drained, overly wet soils or by excessive watering, but sometimes by unfavorable weather. If your gardenias are otherwise growing well, with good color to the leaves, but buds are dropping off, water or weather are the likely cause.
Following excessively hot, dry weather bud drop is prevalent because the plant cannot absorb water rapidly enough to compensate for what it is losing through its leaves. Keeping the soil evenly moist as well as frequent light syringing of the foliage will go a long way toward reducing bud drop under these conditions. Gardenias may also drop their buds following a rapid change in temperature, such as an unseasonably cold or hot spell.
If your gardenias are pale or woody, with lots a leaf drop, there may be additional causes. In my experience, an incorrect soil pH is the place to begin. The soils in our gardens are naturally somewhat alkaline. Gardenias like an acid soil, not alkaline. If the soil pH is too high, fertilizing, especially with iron and trace minerals, will be ineffective. For these nutrients to be absorbed by a gardenia the pH has to be corrected first. Acidic mulches and fertilizers like cottonseed meal, will bring the pH down, but it will take a few months, so be patient.
Many gardenias in local gardens that are pale, iron deficient, woody and miserable will green up, put on new growth and began flowering once the soil pH is corrected.
If you are providing the correct culture, including soil, water and pH and your gardenias are still unhappy, your problem may be more serious. Tiny microscopic pests, known as root-knot nematodes find gardenias a favorite host. These invisible pests feed on the roots of gardenias and slowly drain them of their vigor, damaging roots and preventing the normal uptake of water and nutrients.
Root-knot nematodes are difficult to diagnose on a gardenia growing in a landscape, but an examination of the roots of a dead or dying plant will provide certain confirmation. If root-knot nematodes are the culprit, small irregular nodules, about the size of a pea will be obvious along the roots. Until recently, if nematodes were present there was nothing a gardener could do short of giving up on gardenias altogether and planting something that was resistant to nematodes.
Several years ago a few nurserymen in Florida, where nematodes are even more prevalent than California, began producing grafted gardenias. These grafted plants, now available in limited numbers in California, are nearly immune to root-knot nematode attacks. The grafted rootstocks of these “super gardenias” are also more tolerant to our higher soil pH and irrigation mistakes. When selecting new gardenias to add to your garden, it is often worth searching for the more vigorous grafted plants.
One of the special pleasures of gardening in the mild coastal climate of Orange County is the fragrance of a blooming gardenias. Gardenias are a special gardening pleasure afforded to us, because here, as in few other areas of the country, gardenias can be outstanding garden plants.
Ron Vanderhoff is the Nursery Manager at Roger’s Gardens, Corona del Mar