David Clark asked 15 years ago
I have potatoes in tubs all in fresh multipurpose compost with added Osmocote, religiously watered. In the last 2 weeks some leaves have yellowed between the veins and turned brown. There is no sign of any mould. Dr Hessayon’s book (The Vegetable Expert) suggests it could be magnesium deficiency. If you think this is likely, I would be very grateful if you would recommend a product to boost Mg levels.
1 Answers
Gerry Daly Staff answered 6 years ago
It is hard to say exactly what this is without seeing it, but it is possibly magnesium deficiency. Deficiencies are often triggered by dry conditions. Despite watering, the moisture in compost can still be deficient because of relatively limitied root run. The compost can be heated due to sunlight falling on the pot and this can affect root function. And watering can reduce nutrient levels by leaching from peat-based composts that do not offer the same chemical buffering action that mineral soil does.
Osmocote should deliver enough magnesium but it may have been leached. You could try some liquid feeding in about every fourth or fifth watering, The standard feeds, such as Miracegrow, contain the full range of plant nutrients and should address deficiencies.
