rootrot

Every year one or two of my potted plants suddenly look very ill! Left alone they are doomed and will surely die. From the e-mails I receive I am not alone in having these problems.
It is invariably a case of 'rotting roots' caused by stagnant, waterlogged and under-aerated soil, probably aggravated by the cool English conditions. Although I am well aware of the dangers of over-watering, it still happens.
So here is my recipe for a treatment. It takes a long time for the plant to recover. Sometimes it never does!

1. Typical Symptoms:
A sad looking plant; leaves dropping - especially away from branch tips. Remaining leaves flabby and wilting.
Any fruit small, soft and tending to drop off. Some branches and twigs dying.

This is a lemon with these symptoms. It is about 4' (1.2m) tall and growing in a 10" (25cms) plastic pot. The trunk at soil level is also showing signs of rotting and split bark.

2. Confirmation of Cause of Symptoms:
Gently ease the plant out of its pot. See if much of the compost and roots breaks off in a soggy lump and remains in the pot. Check if gentle shaking or tapping the root ball results in handfulls of roots dropping off. Look to see if any of the larger roots have outer layers peeling off, or are clearly rotting and turning black or dark brown.

4. Trim back all rotten roots to healthy ones:
Try and clear out the central area and loosen tightly intertwined roots, so that fresh compost will reach this area. Leave as many as possible of any healthy, fine feeding-roots.

5. Re-pot with very free draining compost.
Use a pot just big enough to contain the remaining roots. This will be smaller than before.
Tease the compost into the roots and shake or tap the pot to make it settle a bit. Try and raise the level of the plant slightly, compared to its original level. It may now need the support of a stick to prevent movement.

6. Prune very heavily.
Remove virtually all the leafy branches. The trimmed roots will not be able to support them. (Never cut as far down as any graft union.). For a valuable variety it is worth trying to propagate from the prunings.

7. Place in a warm position.
Not in strong sun. Water compost only when surface dries. Never stand in water.

8. Pray, or keep your fingers crossed!
New shoots should eventually appear as the roots re-grow. It can take over a year. As long as a gentle scratch on the bark shows green underneath, the plant is still alive. Feeding is not required until new growth begins.

Here is my suggestion for a well aerated, free-draining compost mix.
Equal parts by volume of:
                          Peat or ready made, peat based compost.
                          Washed silver (quartz) horticultural sand
                          Perlite or Vermiculite (larger particle grade is best)
                          Well composted bark (a type with small bark pieces)