Where
on the lemon tree did this yellowing leaf come from? Why do
horticulturists always ask this question?
Because this problem is usually related to an element (mineral)
deficiency and elements are grouped into mobile elements and immobile
elements. When a deficiency occurs in mobile elements the first symptoms
will appear on older leaves because the mineral moves to the actively
growing younger leaves. The mobile elements are magnesium, phosphorus,
potassium, zinc and nitrogen.
On the other hand, when a shortage of an immobile element occurs, it
is first noticed in the younger leaves because it doesn't move from the
old leaves. The immobile elements include calcium, iron, sulphur, boron,
copper and manganese.
