When fertilized optimally, roses develop substances that protect them from infestation with weakness parasites. However, too much or incorrect fertilizer application can cause an imbalance in the soil and promote disease infestation.
What happens if roses are over-fertilized?
Roses can suffer from excess nitrogen, excess phosphorus or lime chlorosis due to overfertilization. This can lead to poor growth, soft shoots, aphids, mildew and fungal infestation. For prevention, a soil analysis should be carried out and adapted fertilizers should be used.
Soil testing is done 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. Have a soil analysis carried out before planting, which is of course also useful if your roses are often ailing. Many institutes offer special rose nutrient analyzes and can provide you with fertilizer suggestions that are specifically tailored to your soil conditions. This allows you to compensate for both deficiencies and excesses of nutrients.
How to recognize certain fertilizer damage
You can easily recognize indications of certain disorders caused by over-fertilization on the rose petals.
Nitrogen excess
A nitrogen deficiency is rare, but is shown by weak 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 constantly stimulated to grow, can freeze 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.
Phosphorus excess
Phosphorus deficiency also occurs very rarely. You can recognize it by its 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 black mold, a harmful fungus. Special remedies available from specialist retailers (€23.00 on Amazon) can help here.
Calcium chlorosis
However, one of the most common deficiency symptoms in roses is chlorosis caused by an excess of lime. Too high a lime content in the soil makes it more difficult to absorb iron because the substance binds iron compounds in the soil. You can recognize this excess of nutrients by the small, light yellow leaves, where only the leaf veins remain green. Lime chlorosis occurs particularly frequently on loamy, wet soils and as a result of liming roses.
Tip
Roses should never be fertilized when they are planted, but only after they have successfully grown. Otherwise, the roots can be seriously damaged by the excess nutrients. If you want to fertilize right from the start, it's best to use horn shavings - these only become active when they decompose after a while. In general, organic or slow-release fertilizers are better for supplying roses than artificial fertilizers.
