Gardenia shrubs are acid-loving plants and prefer acidic soil types. This means the pH level for your Gardenia bushes should range between a pH of 5.0 and 6.5.
If the ground around your home has a pH of 7.0 or higher, consider growing Gardenias in containers. With their fragrant blossoms and deep emerald foliage, gardenias are a staple of the Southern garden.
Gardenia Quick Care Tips
Botanical name:
Gardenia spp.; the most common garden species is G. jasminoides (syn. G. augusta, G. grandiflora)
Common names:
Gardenia or Cape Jasmine
Zones:
8-11, with a few varieties hardy to Zone 7. In warm regions (Zones 8+), select a spot that gets morning sun and light afternoon shade but that avoids the harsh midday sun.
Bloom period:
May-June, with some varieties experiencing sporadic, rebloom into fall
Flowers:
Gardenia flowers are typically white, with single, semi-double, or double blossoms ranging from 2 to 5 inches in diameter. Some cultivars, such as ‘Golden Magic’, have buttery yellow blossoms.
Foliage:
Glossy, dark green leaves 2 to 4 inches long will remain attractive throughout the year.
All Gardenia varieties thrive in rich, loamy, well-drained soil. Add peat moss or compost to the existing planting area for proper drainage.
But you’ll also need to address your gardenias’ soil pH for healthy growth.
How To Determine Gardenia Soil pH
Test the acidity level of your soil before planting Gardenias like Gardenia jasminoides in your yard or garden.
Use a pH meter or a soil testing kit that includes litmus paper or a chemical solution. These tools are available at garden, hardware, and home improvement stores or online.
To test the soil using a pH meter:
Dig a 4″ inch hole in the soil and fill it with distilled water. Insert the pH meter probe into the soil to get a soil pH reading.
To test the using a soil test kit:
Follow the instructions on the kit for the best results.
In general, take and add a soil sample and distilled water to the testing bottle provided and shake. Add the reagent, or use the litmus strip to test the soil.
Use the color chart provided to determine the pH level. It prefers fairly acidic soil (a pH of 5.0 to 6.0), likes a tropical climate (but suffers in too much direct sun), and doesn’t transplant well.
Test several soil samples in the area where you plan to plant your gardenia shrub. Soil pH can vary from section to section.
How To Prepare Soil Mixture For Planting Gardenias
If your soil pH tests higher than 6.5, the soil is too alkaline for gardenias. To increase acidity (lower the pH), add sphagnum peat or blood meal to the soil.
NOTE: Yellow leaves can indicate a high pH or possible iron deficiency, while green leaves tell you the pH is perfect.
Spread a 1″ – 2″ inch layer of sphagnum peat over the soil. Mix well into the top layer of soil (8″ – 12″ inches) before planting your gardenias.
You can also use granular sulfur or an acidifying fertilizer.
If your soil test results show pH levels lower than 5, your soil is too acidic. Decrease acidity (increase the pH) by adding ground limestone or hydrated lime to the soil.
Follow the instructions on the product package to avoid over-limiting. The amount of ground limestone or hydrated lime to add depends on the type of soil you have: sandy loam, loam, or clay loam.
Use the “jar test” to determine the soil type, or send a soil sample to a testing lab for analysis. Local testing labs will also test your soil pH.
You can also mix wood ashes into the soil to decrease acidity.
Coffee grounds are popular for increasing the acidity in soil but have a neutral pH rating. This means, in most cases, coffee grounds won’t do much to change the soil pH.
More on: Coffee Grounds For Gardenia Plants
Keep in mind that raising the acidity or lowering the alkalinity of your soil may take a month or more.
If your soil measures above 7.5, it’s difficult to lower the alkalinity. Consider mixing your own soil and planting the gardenias in pots instead.
How To Ensure Proper Soil Drainage
To test soil drainage, dig a hole and fill it with water. Soil that drains well should drain right away. If the water takes a few hours or a day to drain, the soil has poor drainage.
Build a raised bed (a large mound of soil or use railroad ties) to ensure proper drainage. If adding pre-mixed soil to the native soil found in your yard, make sure to mix the soil before building a mound.
Test the soil after mixing to ensure a suitable pH level.
If you need to add peat moss to change the soil’s pH, avoid creating a soil mound. When clumped together, peat moss causes water clogging, which can kill your gardenias. Instead, install drain tiles.
Sun exposure is necessary for proper flower bud development. With too little sun, plants will produce leggy growth and few flowers. On the other hand, too much sun can cause blooms to fade quickly.
The same drainage test applies when potting Gardenia plants. If you notice the water isn’t draining, dig a small channel around the pot’s edge to create a mound for better draining.
Potting Gardenias: Should You Mix Your Own Soil?
To mix your own soil when potting gardenias, include the necessary ingredients to create acidic soil.
To mix soil-based potting media:
- 2 parts peat moss
- 1 part sterilized house plant potting soil
- 1 part sand or perlite.
Mix these ingredients, then test the soil. Add limestone or gardenia fertilizer to adjust the pH levels.
You can also mix this soil with native soil found in your yard or garden. Make sure to test the pH after mixing to ensure the proper pH level.
Consider buying pre-mixed potting soil such as Miracle-Gro Potting Mix, Miracle-Gro Indoor Potting Mix, or FoxFarm Ocean Forest Garden Soil. These soils have the pH range needed to grow Gardenias.
How to Plant, Grow, and Care for Gardenias
Keep watering consistent. Gardenias will suffer if they dry out or are overwatered.
Gardenias enjoy high humidity. Mist with water during dry spells.
Fertilize with a slow-release fertilizer formulated for acid-loving plants such as rhododendrons and azaleas a couple of times during spring and summer. Do not fertilize in the fall, as this can cause a spurt of frost-tender growth.
Routinely remove faded flowers to encourage more blooms.
Bud drop can be caused by low humidity, over- or under-watering, insufficient light, and high temperatures.
How to Grow Gardenias Indoors
- Gardenias grown indoors need 6 to 8 hours of bright, indirect sunlight through a window.
- The gardenia is very sensitive to temperature changes, so keep it away from air conditioning, heat vents, and drafty windows.
- The plant prefers 70ᵒF (21°C) during the day and 60 to 65ᵒF (15 to 18°C) at night.
- The gardenia likes high humidity. To increase humidity, place the potted gardenia on a shallow tray with gravel and water. Water will evaporate and increase the relative humidity around the plant. Alternatively, place a humidifier close to the plant or mist the leaves often with water.
A plant will drop its flower buds before opening if water stress is an issue. To avoid this problem, maintain evenly moist soil, but avoid overwatering, as gardenias do not like wet feet.
Mulch plants to help maintain even soil moisture. Mulch is also important for weed management around plants because shallow-rooted gardenias do not tolerate cultivation.
How to Propagate Gardenias
- In early spring, take a 4-inch stem cutting just below a leaf.
- Dip the end of the cutting in the rooting hormone.
- Put the cutting into a pot with a mix of perlite and potting soil.
- Keep the soil moist.
- Transplant the cutting into a bigger pot after it has been rooted.
Common Pests & Plant Diseases
Pruning should only be done after the shrub has stopped flowering and before October. Pruning after then will hurt the next season’s flower production.
The most common problem encountered with growing gardenias is pests. Mealybugs, aphids, scales, and whiteflies are all problematic in gardenias.
Extra humidity is important in keeping down spider mites that thrive under dry conditions. during their growing season (March to October) with a dilute fertilizer for acid-loving plants.
Try using insecticidal soaps or horticultural oils; these can usually keep pests in check when used properly. Root-knot nematodes can also be a problem, but there are currently no chemical treatments available.