With optimal fertilization, roses develop substances that protect them from infestation with weak parasites. However, too much fertilizer or the wrong amount of fertilizer can cause an imbalance in the soil and promote disease infestation.
Overfertilization can manifest itself in different ways
The soil sample is to be taken before fertilizing
As various scientific studies have shown, many home gardens are oversupplied with nitrogen and phosphorus, but there is often a lack of potassium. Before planting, have a soil analysis carried out, which of course also makes sense if your roses are often ailing. Many institutes offer special rose nutrient analyzes and can provide you with fertilizer suggestions that are specially tailored to your soil conditions. This allows you to compensate for both deficiencies and excess nutrients.
How to recognize certain fertilizer damage
You can easily see indications of certain disorders caused by over-fertilization by looking at the rose petals.
excess nitrogen
A lack of nitrogen is rare, but shows up as poor growth, small, yellowish-green leaves and few flowers. An excess of nitrogen, in turn, leads to soft shoots and leaves, which are increasingly attacked by aphids. Due to the excess of nutrients, the rose shoots do not mature, after all they are stimulated to continue growing, can freeze to death and are also susceptible to powdery mildew and bark spot disease (also known as bark blight). You can counteract this with potassium fertilization, as this substance promotes shoot maturity.
excess phosphorus
A phosphorus deficiency is also very rare. You can recognize it by the thick, blue-green leaves with purple edges and undersides. On the other hand, excess phosphorus is much more common, which in turn promotes infestation with blackspot, a harmful fungus. Special agents available in specialist shops can help here.
calcareous chlorosis
However, one of the most common deficiency symptoms in roses is chlorosis, which is caused by an excess of lime. Too high a lime content in the soil makes it more difficult to absorb iron, since the substance binds iron compounds in the soil. You can recognize this nutrient surplus by the small, light yellow colored leaves, where only the leaf veins remain green. Lime chlorosis occurs particularly frequently on loamy, wet soils and as a result of liming roses.
tips
Roses should never be fertilized when they are planted, only after they have successfully established themselves. Otherwise, the roots can be severely damaged by the excess nutrients. If you want to fertilize right from the start, it is best to use horn shavings (€32.93) - these only become active when they decompose after a while. In general, organic or depot fertilizers are better for the care of roses than artificial fertilizers.