For plants to successfully grow, flower and fruit they need nitrogen, potassium, phosphorous and different trace elements. Without one or more of these, plants will start to display physiological symptoms – low nitrogen causes weak, yellow leaves, while a potassium deficiency results in poor harvests and discoloured foliage. Trace elements include manganese and iron, and it’s deficiencies of these that are most frequently encountered, resulting in yellow leaves and brown edges.
In summer, raspberries fail to thrive, the crop is poor and the leaves have a general unhealthy look.
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Pelleted poultry manure gives a quick boost of nitrogen, while organic compost gives a longer-term solution. Add bonemeal if your raspberries are short of phosphorous. In general, if you’ve added plenty of well-rotted compost to the soil to improve moisture retention, drainage and soil structure, you’re unlikely to have too many problems.
Add sulphate of ammonia for nitrogen deficiency. Sulphate of potash cures potassium deficiency. For low phosphorous levels, apply super-phosphates. Top up manganese levels with iron chelate and use Epsom salts to tackle magnesium deficiency.