Defoliation

MANY years ago, when I was a student, I had a friend who was doing his
PhD on the translocation of nutrients in tomatoes. He used radioactive
isotopes then followed their movement within plants using a Geiger
counter. He found that as leaves senesce, the nutrients contained in
them were translocated back into the stem and then to the young
growth, to nourish the new leaves. This translocation continued until
the old leaves were completely dried up, and in the case of
phosphorus, it was still being returned to the rest of the plant even
when the old leaves were completely yellow.

This means that, with few exceptions, the old leaves should not be cut
off until they are completely dead, the main exception being if the
old leaves are diseased and should be removed in order to limit the
spread of the disease onto the new growth. In that case, the plant
should be given a boost of fertilizer to replace the nutrients that
have been removed in the leaves that have been cut off.

Patrick Alexander

It's interesting information but its presentation doesn't quite strike me as having peer-reviewed scientific reliability, esp not for a single plant group. Having said that, good to keep in mind for those marginal growers, perhaps.

KarinL