incorrect soil pH – gardenias prefer acidic soils. If growing in alkaline soils gardenias have trouble accessing all the nutrients they need and yellow leaves can develop. Apply sulphur to the soil to make it more acidic.
From one of the top names in gardening aids, the best overall pick for feeding gardenias is Scotts Miracle-Gro Miracid Acid-Loving Plant Food. This water-soluble fertilizer is designed to be mixed with water and poured over foliage or around the base of the plant.
Sulphur. This is the common acidifying material. Soil organisms convert sulphur into sulphuric acid, so acidifying the soil. The more finely ground the sulphur the more quickly the bacteria can convert it; sulphur dust is quicker acting than sulphur chips (and more expensive).
Feeding and mulching Gardenias are fed during the growing season from spring to autumn with a complete fertiliser such as Seasol plus Nutrients Roses & Flowers. Water it in well after application. Plants also benefit from liquid feed such as PowerFeed PRO SERIES for Roses & Flowers during the growing season.
The thinking behind this practice is that the yellow leaves are a sign of magnesium deficiency. Adding Epsom salts, or magnesium sulfate, is supposed to replenish the missing magnesium, perking up the gardenia in the process. Some gardeners recommend a one-off dosing, others a feed at regular intervals.
Gardenias use a lot of nutrients to produce so many glorious blossoms. Feed your shrubs by applying an acidic, slow-release fertilizer such as an azalea or camellia fertilizer. For the organic gardener, blood meal, fish emulsion or bone meal work well.
Prep garden soil by sprinkling up to one cup of Ultra Epsom Salt per 100 square feet, and then work it into the soil before seeding or planting. This helps the seeds to germinate and start with a strong, healthy growth.
Though vinegar can be fatal to many common plants, others, like rhododendrons, hydrangeas and gardenias, thrive on acidity which makes a bit of vinegar the best pick-me-up. Combine one cup of plain white vinegar with a gallon of water and use the next time you water these plants to see some amazing results.
Nitrogen deficiency shows as yellow between the veins at any time through the year. Aged fowl manure or Blood and bone meal applied at one handful per square metre and watered in well every eight weeks from Spring through Summer will address this deficiency.
Fertilising Gardenias
Every 2-3 months from spring to autumn feed with a dose of cow manure and a bit of Certified Organic fertiliser if your soil is particularly poor. For really strong, healthy growth and large blooms we also recommend fortnightly applications of OCP eco-aminogro and OCP eco-seaweed.
You can increase the acidity of your soil by adding things like compost and manures, leaf litter and mulch. Iron chelates work too. In extreme situations, you can use powdered sulphur - one handful per square metre, once a year. Sulphur works very slowly and you won't notice a change in your pH for about 6 months.
Add organic matter.
The most organic way to lower your soil's pH level is to add soil amendments. Use organic materials like mulch, pine needles, sphagnum peat moss, compost, and coffee grounds.
Because gardenias need all three essential macro-nutrients (nitrogen, phosphorus, potassium) and also a good dose of micro-nutrients such as iron and manganese, you should feed them with an organic fertiliser such as Dynamic Lifter.
Are Coffee Grounds Good for Gardenias? Don't worry about adding more coffee grounds to your gardenia soil; these flowers absolutely love coffee. In addition to being an excellent source of nitrogen, the acid in coffee lowers the pH of the surrounding soil, stimulating the roots of acid-loving plants such as gardenias.
Osmocote is one of the most popular and well-respected fertilizer brands and when it comes to gardenia fertilizers you can't go wrong with this plant food. What you'll love about this product is that it is easy for beginner gardenia gardeners. All you need to do is apply it once every 6 months.
It affects a range of plants including gardenias, rhododendrons, azaleas, camellias, roses and citrus. The solution is to get some Epsom salts. Take half a litre of water, and put in half a teaspoon of Epsom salts, then shake and stir. Either water it on plants or you can foliar spray it.
Young gardenia leaves turning yellow is likely from low iron. All can be fixed by giving your gardenia a dose of an acidic nitrogen fertilizer containing micronutrients. Once your gardenia leaves are green again, use the fertilizer twice a month from early spring to late summer.
Feed gardenias monthly from late spring to the end of summer, when they actively take up nutrients. Use poultry manure sparingly or feed with a flower and fruit fertiliser or seaweed tonic. Gardenias also require protection from intense sun.
Spraying your gardenia with an antifungal agent (such as horticultural oil with baking soda and insecticidal soap) can reduce the risk of infection or infestation.
Increase soil acidity
Leaving the banana skin soaked in water to ferment for a month will turn it into vinegar. Acidic soil-loving plants like rhododendrons, hydrangeas, and gardenias will especially love this special treatment.
Plants like azaleas, gardenias and blueberry bushes need acidic soil to thrive, that's why ACV with 5 percent acidity works well as a fertilizer for certain flora.
Eggshell Benefits
As it happens, eggshells can provide all the calcium carbonate the soil needs, which helps to lower the soil's pH level and make it more alkaline as opposed to acidic. This is incredibly beneficial for plant growth because many plants prefer to grow in soil that has low acidity.
Which plants shouldn't you try this with? Don't add eggshell fertilizer to plants that prefer acidic soil, like blueberries. Ericaceous plants such as mountain laurel, pieris and azaleas also fall into that category.