A lot of our Melbourne customers have noticed how healthy and green our Gardenias are recently. What is our trick?
Well, firstly, let’s talk about why Gardenias sometimes aren’t green. Simply stated, it is a lack of nutrients, and is referred to as chlorosis. But simply feeding them will a general purpose fertilizer won’t keep them from suffering. The story is a bit more complicated, involving both soil Ph and temperature.
Chlorosis occurs when the plant cant take up sufficient iron or manganese. Iron and manganese may be present in the soil, but when the Ph is over about 6.5, is not available for the plant to take up, leading to chlorosis. This can be overcome by using a fertilizer that has chelated iron in it. Chelated iron is iron that has been bound to another molecule, to enable it to be taken up by the plant, even where the Ph is above 6.5.
Temperature also plays a part as all chemical reactions slow down as temperature decreases. Even in soils that a moderately acidic, nutrient uptake can be too slow during cold weather to keep the plant looking healthy.
Because of this, gardeners in Melbourne are often advised to plant Gardenias in full sun, to keep them warm during winter. However, in warmer climates Gardenias thrive in lightly shaded positions, and in Melbourne in summer Gardenias can suffer from dehydration and scorch.
Consideration should be given to finding a lightly shaded spot that could benefit from some extra heating. Planting near to large areas of brick or stone can help, as these will absorb warmth from the sun and radiate it back out at night.
A lightening of the leaves is unavoidable in most outdoor plantings of Gardenias in Melbourne, but it is possible to still keep them looking reasonably good by using a targeted top-dress. We use one that has a mixture of short and medium term release chelated iron, with other important trace elements such as manganese and zinc.
An application of this in Autumn, and another in Spring, helps to fortify the plants and get them through the coldest months. We now sell this topdress in convenient 1.5kg bags.