Roses are extremely heavy consumers. If you want to enjoy them for a long time, regular fertilization is essential, whereby the plant should be supplied with essential nutrients such as nitrogen, phosphorus, potassium, manganese and magnesium - but not in excess! Calcium or lime is not one of them, on the contrary: You should better avoid fertilizing with lime.
Roses do not need to be whitewashed
Lime roses or not?
In some gardening guides you can read that roses should be whitewashed a few weeks before planting in order to adjust the pH of the soil to the optimum value between 6 and 6.5. If this is not done, there is a risk of lack of growth, and the flowering will not be as lush as desired. Well, you don't have to worry: In this country you can very well do without liming the soil without fearing any damage - there are of course rare exceptions, but for this reason you should have a soil analysis carried out before planting to be on the safe side.
Chalk chlorosis is one of the most common rose diseases
Instead of a calcium deficiency, calcium chlorosis is one of the most common deficiency symptoms in roses. If the lime content is too high, the absorption of iron compounds is made more difficult, since lime binds the important nutrient iron in the soil. As a result, very calcareous soil often leads to an iron deficiency. The leaves remain small and turn light yellow, only the leaf veins remain green. Yellow or chlorotic leaves are commonly seen in rugosa roses (i.e. potato roses) growing in loamy, waterlogged soil. Wetness and poor drainage can also lead to chlorosis in other roses.
How to treat calcareous chlorosis
If chlorosis occurs, you can remedy this by first loosening the soil and working iron chelates into the soil or spraying iron preparations; ask your specialist dealer for advice on this. On the other hand, you should only lime the soil if the pH value is below 6 (exception: Rosa rugosa). You can measure the pH value yourself regularly using a suitable pH set from specialist retailers. Otherwise, it is advisable to have a soil analysis carried out every three to four years. Agricultural inspection offices create detailed analyzes and also make fertilizer recommendations.
tips
In addition to lime chlorosis, incorrectly fertilized roses also quickly have an excess of nitrogen. This leads to soft parts of the plant, which are heavily attacked by aphids. Over-fertilization with nitrogen can be remedied with potassium.