By Wendyk
United Kingdom 
I have just started using a new greenhouse. Most of what I have planted , tomatoes, cucumber. spinach, bedding plants etc, all seem to have pale yellow discolouration on the leaves. The cucumber plants have yellowing around the edge of the leaves. Does anyone know what I can do to rectify this ? The plants look healthy otherwise.
17 May, 2011
Answers
Sunburn is usually a broad, yellow to white spot in the center of the leaf. Yellow edges are usually a symptom of nutrient deficiencies, or drought.
18 May, 2011
My first guess would be a nutrient deficiency. Is it the lower, older leaves which are yellowing? If so, the most likely culprit is a nitrogen deficiency. A nitrogen-rich liquid feed will give them a quick boost. Other nutrient deficiencies can also cause yellowing leaves, as can pest attacks.
18 May, 2011
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It sounds like the plant equivalent of sunburn! You might want to put some shade paint on the glass.
17 May, 2011