Gardenia shrubs are acid-loving plants and prefer acidic soil type. 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 your Gardenias in containers.
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 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.
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 to the soil.
NOTE: Yellow leaves can indicate a high pH or possible iron- deficiency. 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 liming. 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.
Keep in mind that it may take a month or more to raise the acidity or lower your soil’s alkalinity.
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. Peat moss, when clumped together, causes water clogging, which can kill your gardenias. Opt for installing drain tiles instead.
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 a 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.