Helping sickly potted plants
Q
Some of my potted plants (both indoors and outside) have turned pale and anaemic. Feeding them seems an obvious solution, but will this sudden boost give them indigestion – and should I repot them first?
ALeaves turn yellow for a variety of reasons, but the main cause is an inability to make the green pigment chlorophyll, hence the technical term chlorosis. Nutrient deficiency is one of the most common problems, but anything that interferes with the ability of roots to take up nutrients can also be to blame. Overwatering could have suffocated some of the roots, while temperatures lower or higher than optimum can cause yellowing.
Citrus leaves often fade when temperatures dip below 45°F (7°C). Pests sucking sap from leaves often cause a stippled kind of yellowing, while viruses leave spots and streaks. Plants are individuals with different needs, so try analysing your plants one by one to work out why they have lost their looks.
You are right to question whether feeding a sick plant is wise, because their roots will not be active enough to make use of it. Yet from spring onwards, most plants have recovered from the rigours of winter and, unless they’ve been overwatered, should benefit from a well-balanced liquid feed with added trace elements, perhaps at halfstrength to start with. If a plant is sound, I might feed it, prune away some sickly growth and, after a while, pot it on or prune the roots and repot back into the same container.
Potted camellias, skimmias and rhododendrons are hungry feeders and if they are in limy compost or repeatedly watered using hard (alkaline) tap water, they will struggle to absorb iron and manganese, ending up with limeinduced chlorosis. Prune away some of the chlorotic growth, repot into ericaceous compost and, if hard tap water has to be used, add a feed for acid-loving plants at half strength. Citrus need a wide range of trace elements and are best fed regularly with special citrus summer and winter feeds.