CulturalAdvice

WATERING. Again it is death to over-water, or leave standing in waterlogged conditions! It is better to err on the dry side. If the leaves start to look a little limp, then water promptly and thoroughly but let all excess drain away. If you live in a very hard water area, use rain-water and not tap or chemically softened water.

TEMPERATURE. In summer plants will grow happily outside in a reasonably sunny spot in the UK. A greenhouse, unless well shaded and well ventilated, will sometimes get too hot. Over 30C is getting too hot.
In winter, I try and maintain about 5C to 10C. But an occasional few hours just below freezing won't do too much harm to most varieties. Poncirus Trifoliata hybrids will survive lower temperatures.
Try and maintain air circulation, as this helps to prevent botrytis developing.

FEEDING. Specialist citrus foods are available but tend to be expensive. Citrus require high nitrogen when growing, and high trace elements. I use cheaper soluble, balanced-formulae foods that are commonly available in garden centres and feed every watering. This naturally results in less nitrogen over winter as watering requirements reduce. Each Spring I give one dose of a Magnesium supplement and one dose of Sequestered Iron to all except young seedlings. This regime seems to eliminate any 'chlorosis' or leaf yellowing.

INDOORS. Difficult. Too dry with central heating, and likely to be sudden changes of temperature and lighting conditions. Warm, dry and dim light results in leaf drop. Try and avoid these states, and mist spray leaves with water regularly.

WINTER LEAF DROP. This seems to be a common problem and has been much discussed in Citrus circles. It is often attributed to low light, but I have seen mature potted trees over-wintered happily in very dim conditions. I believe the problem is probably due to sudden changes in light and temperature, to which the plant cannot respond quickly enough, and to low light conditions when temperatures tell the plant that it should be growing.

PESTS. I've had scale of several varieties, whitefly, various aphids (black, green and recently a large dull-pink variety) and red-spider mites. One variety is common on citrus and is bright red. The other is the more usual glass-house mite. I try and use biological control with varying success. Then I spray twice a year with 'white petroleum oil' which smothers many pests. This is probably only available from a friendly horticultural chemical supplier. My huge pot has lasted for years and was manufactured by Hortichem.
Finally, if absolutely needed, I spot-spray with other chemicals. If you are using biological controls, then of-course you should isolate any problem plants, and spray them in a different location. If the pest is spotted early this also reduces the likelihood of rapid spread to nearby plants.
See also my page about citrus leaf miner.

page updated 18th June 2002

Normal scale and black parasitised scale.

Both scales have now been attacked and turned black.

The wasp has now emerged from the right scale, leaving a circular hole.

My most consistent success is the use of the predatory wasp Metaphycus Helvolus against soft scale. I introduced this predator into my greenhouse about 10 years ago and it's still there, as evidenced by these greatly enlarged photos of black parasitised scales and normal scale insect. The scales shown are about 1.5mm long. The black scales die as young wasps develop within and emerge to complete the cycle.

My worst pest used to be Citrus Red Mite, which always seemed to come back. These photos show the typical mottled leaf as the mites suck out the chlorophyll. On the right is my best close-up attempt to photograph the mites. I have tried using biological control in the form of Phytoseiulus Persimilis and Typhlodromus Occidentalis. The first had no effect that I could detect. The second may have worked a bit, but I can no longer find a supplier in the UK.
Finally an expensive chemical spray cured the problem. For details visit my page about citrus leaf miner.

BIOLOGICAL CONTROL is too great a subject for this site to cover in detail, but details of my attempts are shown below. Have a look at the site of the Dutch company 'Koppert' or the UK company 'Scarletts'.

Citrus Red Mites viewed from above

Citrus Red Mite from below

For the periodic aphid infestations which occur, I have used another parasitic wasp called Aphidius. These lay eggs in the Aphids which become 'mummified' before the young wasp emerges. The photos show dead Aphids with the emergence holes clearly visible.

My daughter's birthday present was an Intelplay QX3 computer microscope, specially obtained from USA, but now also available in the UK. Here are some images from it. Optical magnification is quoted as x200, but I guess these insects are about 0.3mm long. Click here for more Citrus Red Mite images.

This advice is based on personal experience of growing potted citrus in England for over 20 years.

GROWING MEDIUM. Must be free-draining and of an open texture, especially for young plants. The easiest way to kill citrus is to provide soggy conditions with dense soil. The roots simply rot away! I have spoken to commercial growers of potted citrus and they recommend using peat-based compost with fairly 'chunky' composted bark incorporated to provide the open texture. About 25% by volume of perlite improves drainage. As the plants grow larger, I add more soil-based compost (such as the UK sold John Innes 3) to provide weight and stability to the pot. The growing medium should be neutral to slightly acidic, although this can depend on the exact root-stock used.

The University of California has a system for producing young potted citrus of the highest quality. This uses a 50% peat+50% fine sand mixture with added nutrients and trace elements. Variations replace the sand, or some of the peat, with perlite or vermiculite. If you have access to the correct ingredients this is probably the best growing medium of all. Full technical details can be found at a series of on-line lecture slides beginning here.

Sciarid flies, or fungus gnats, is another pest that is associated with using peat-based composts. Leaving the surface damp for long periods encourages them. The larvae then destroy seeds and attack the roots of small seedlings. An unusual way of reducing numbers of these small flies is to intersperse a few plants of Pinguicula weser among the pots. This bog plant gets its nourishment by catching small flies on the tiny sticky drops which cover the leaf surface. I have found this to be quite effective. The photo shows how large numbers of sciarid flies - plus some whiteflies - have been caught.As a bonus the plant produces attractive small pink flowers.