Member11 Dicembre 2022 at 11:39
Here in The Netherlands we use bitterzout (epsom salt?), MgSO4 for spraying the leaves.
Normally you apply every few years calcium to the soil, for keeping the pH at a good level. Dolokal als calcium fertiliser contains 5 – 10 % Mgo, so that’s a good way to rise your Mg level if there is a deficiency.
But some grape cultivars do have problems to take op MgO in there youth. Even if there is enough MgO in the soil, you see deficiency on the leaves. After 5-7 years, it becomes beter.