Usually first noticed by leaves turning yellow or orange and a "woodiness" of the plant.
Usual causes are nutrient deficiency (or imbalance), a pH significantly lower than 6.5, or water deficiency.
All of these faults are not uncommon when the plants are in pots. Pots have a finite nutrient and water capacity and if the potting compost used is soil-less it could have a too low pH.
Whether in pots or in the ground, the solution is to monitor the condition of the plant and, if felt necessary, carry out a pH test (a few £) or a 3 or 4 element analysis (by a soil laboratory and more expensive) and rectify.
Care should be taken when liquid feeding at the end of the growing season. As the days grow shorter, transpiration and growth slows, and even though warm days are experienced at end of September or beginning of October, Nitrogen burn may occur, with the edges of leaves turning brown. This will grow out but not until the following spring. Stop feeding after the first week of September.
Water logging can give rise to stagnation problems, and this, or soil compaction or drought, can also reduce the plants ability to take up nutrients.
Spring frost may damage young leaves causing a pale brown or bleached appearance. This is not an enduring problem, the plant quickly recovering with new growth later.
To retain moisture and keep down weeds, mulch with matured (dark brown, sweet-smelling) wood chips, leaf mould, well-rotted compost or stones. If limestone chips are used this might be a good counter to the effect of a low pH container compost, but be careful when applying as limestone dust can stick to the leaves. Its use could also give rise to a very high pH.
To reduce the frequency of watering in pots, a water retentive polymer can be used but the effect of this in the winter months has not been established.