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Care of citrus
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Notes on Conservatory management

Summer in the conservatory begins in April and continues through to the end of September, so this is the time you will want to enjoy it most: relaxing and watching the plants growing and flowering around you.

In the summer the plants will need plenty of water and regular feeding but all the other jobs, such as pruning and repotting, can be carried out between Autumn and Spring.

In the very hot sun, ventilators and windows should be open as much as possible, and blinds let down if you have them. Otherwise paint the roof glass with Vari-Shade or Coolglass for protection.

Management and Hygiene

General hygiene is very important in a conservatory, especially in one devoted to plants. Its warm climate encourages the growth of algae and slime and is the perfect breeding ground for bugs and disease. For this reason it is important to start by using only sterilised compost and clean pots, and not ordinary garden soil which is already full of potential infestation.

Other than the usual housework, a thorough cleaning-up operation should be carried out twice a year; in Autumn Oct-Nov, and again in Spring, March-April. This can coincide with the Autumn pruning and the Spring repotting.

All surfaces, especially those near plants, and window frames, doors, floor and window-sills should be wiped over with diluted Jeyes Fluid, the traditional greenhouse sterilizer. Pots can be moved outside on a fine day and the saucers on which they stand should be scrubbed. Tidying operations can include putting plants to rest elsewhere for the winter, such as geraniums and fuchsias, clearing away dead leaves from beds and pots, and cleaning windows and roof glass. K16 is a horticultural glass cleaner which removes algae and dirt easily and may be bought a most garden centres. As the usual greenhouse methods of soil sterilisation cannot be used without damaging plants in beds, care must be taken to keep the soil as clean as possible. Remove the top 2 inches of loose compost and replace it with fresh. Finally, when all is done, sponge down the leaves of foliage plants such as Monstera Deliciosa with Bio Leafshine or a soft soap solution.


Watering should be done in the evening preferably, otherwise the early morning, to avoid the scorching of leaves by the intense rays of the sun through glass. Spray the leaves occasionally at the same time; more frequently in hot weather. User rainwater for this purpose, if you have it, to avoid leaving hard water deposits on the leaves when dry. Otherwise main water is fine for general water, except for lime-hating plants: in these cases use only rainwater be used on the lime-hating plants such as Gardenias, Azaleas, Rhododendrons or Camellias. Although not always possible, it is better to use tepid water, especially in the winter to avoid chilling the plants. Keep a can filled between waterings for this purpose.

In summer (April to September) you should water frequently and never let a plant dry out. In winter most plants should be kept on the dry side. Start to decrease watering in October depending on the weather, and gradually increase it again in March.

It is more common to over-water than under-water, and over-watering or letting a pot stand in a full saucer of water will soon turn the soil stagnant. As a general rule plants should be given a good soaking until the water trickles out of the pot’s drainage holes, and then left until the soil is dry on top before watering again. If a pot has become so dry that the compost has shrunk leaving gaps around the edge, immerse the complete pot in a bucket of water until air bubbles stop coming up. This will ensure good absorption of water, and avoid it just running down the inside edge of the pot. In the summer you may have to water every day; in the winter not more than once a week.


Twice a year, it is a good idea to wash through the compost of pots with plenty of clean water to clear away any excessive build up of fertiliser salts. If possible, this is best done when the plant is outside, so that all run - through water can drain away easily without making a mess of your conservatory floor.


New potting compost will provide nutrients for about 3 months; gro-bags for about a month only. After this, during the summer (April-September) plants will need feeding with artificial fertiliser every week or two. Do not use manure! Plants in beds tend not to need as much feeding as those in pots.

Chempak produces several formulas for different purposes and comes in the form of soluble crystals.

Phostrogen is an all-purpose food also in soluble crystal form.

Sequestrene is an iron tonic good for lime-hating plants and especially useful if the mains water is alkaline.

Liquinure is a general purpose food in liquid form. It probably leaves less mineral residue on the soil surface, but is more expensive than crystals.

Maxicrop + Iron is a good liquid feed made form seaweed, incorporating iron and trace elements, and is recommended for citrus trees to avoid yellowing of the leaves.

Follow the directions on the labels and feed little and often.

CITRUS FERTILISER: High trace element fertiliser for citrus and chlorotic plants.


The most convenient time for this, and the best for plants, is the spring, in either March or April. Plants should be repotted into a larger size as soon as the roots start to appear through the drainage holes; or you can check the root growth by holding the plant upside down and gently tapping it out of its pot. If the roots run tight circle around the outside, the time has come to put it into a larger pot.

Mature plants which are already in larger pots will obviously not be repotted, but may need inspecting and their roots pulled out and trimmed back every year or so. At this time a little fresh soil may be added. Pots can be tidied up occasionally by scraping off some of the surface soil and topping up with fresh compost. Do not do this with citrus as you will damage their top feeder roots.

Make sure that new pots and the gravel, crocks or stones for the bottom are clean. Put enough crocks into the pot to cover the holes and then a layer of compost to bring the plant up to an inch or so below the rim of the pot. Pull out old embedded crocks from the rootball of the plant and loosen the roots a little. Hold it in the centre of the new pot and fill in with new soil, tapping it on the ground gently to pack it in. Firm down a little and water well.

For young plants and seedlings, use John Innes No.1 compost; pot on into No. 2 and use No. 3 for mature plants and shrubs.


The most convenient time to cut back plants is in the autumn, after they have flowered and made most of their growth. However those which are still in flower can be left until the early spring, if preferred. Established climbers in beds should be cut back in the autumn in order to allow as much winter light as possible to the other plants in the conservatory. Many foliage plants are not pruned at all; some of them need only to be tidied up.

Pest control

Many species of insects and creepy-crawlies will be attracted by the warmth and shelter of a conservatory, some of them harmless but others not. The harmful ones should be recognised and dealt with as quickly as possible before their numbers build up, and the under sides of leaves should be examined regularly for signs of an infestation. To help you identify them, I would suggest that you buy a book such as Collins Guide to the Pests, Diseases and Disorders of Garden Plants by Stefan Buczacki and Keith Harris, which has a section on glasshouses.

The most common enemies in the conservatory are aphids (greenfly and blackfly), whitefly, red spider mites, scale insects, mealybugs and thrips. You will also find the occasional slug, snail or caterpillar. All of them feed on the buds, flowers, leaves and stems and, unless checked, will do lasting damage to the plant.

  • Aphids: small green, yellow, brown or black crawling young and winged adults which feed in clusters usually on new growth and buds, sucking the sap. Leaves become sticky and ‘sooty’.
  • Whitefly: tiny white moth-like insects easily put to flight. Look at undersides of leaves. Eggs are whitish and opaque. They suck sap and leaves become sticky and sooty.
  • Red Spider Mites: Seen as tiny red or yellow crawling dots on undersides of leaves which suck the sap. Leaves become speckled yellow and dried out. Mites spin webs around shoots and in leaf axils which are destroyed.
  • Scale Insects: Brown, yellowish or white oval scab-like insects usually found on undersides of leaves and on stems. They appear motionless. Leaves become sticky and soot.
  • Mealybugs: Small oval soft-bodied insects, covered in a waxy meal, which nest in a quilt of white ‘cottonwool’ in leaf axils and on stems. The leaves becomes stick and sooty.
  • Thrips: Narrow-bodied winged and wingless insects, either yellow, brown or black. Attack leaves, buds and flowers which become distorted and covered with a fine white flecking.
  • Slugs, Snails and Caterpillars: All eat holes out of leaves and flowers. Slugs and snails leave slime trails; caterpillars sometimes spin webs around the tips of the shoots.
  • Gardeners who are used to chemical sprays and fumigants in the garden and greenhouse will soon discover that these are undesirable, if not dangerous, when used in what is essentially another room in the house, and will want to restrict them as much as possible. Apart from the harm these may cause to humans and pets, they will also destroy the many harmless and beneficial insects such as bees and ladybirds, which will fly in and out of the conservatory.

The most suitable method of controlling pests in the conservatory is the biological principle, with a back-up if necessary of chemical insecticides in the winter. Biological control can only be used in the warm summer months, and during this time it should be possible to reduce numbers of pests to a level which can be controlled in the winter months with just an occasional spraying.

Biological control

This involves the introduction of the natural predator or parasite of the pest, and these can be bought by mail order as eggs or pupae from the specialist suppliers. They will recommend the quantity you will need which will depend on the size of the conservatory and the number of plants in it. All are available from Scarletts.

It is important that you place an order as soon as the pest are noticed, as numbers can build up very quickly, and time has to be allowed for postage and the hatching out of predators. They will arrive with instructions on their use. Plants must me checked regularly to make sure that they are doing their job. If there are too few predators, another batch will need to be ordered, and suppliers usually recommend several re-introductions over a period of time. The following can be ordered from Scarletts:

  • Aphid predator - Aphidoletes aphidimyza - a midge with long legs which becomes active at dusk. Larvae attack aphids and parasitise them.
  • Whitefly parasite - Encarsia formosa - small black and yellow tiny ‘wasp’ which lays eggs into whitefly grub which is then eaten by the growing larvae.
  • Red Spider Mite predator - Phytoseiulus persimilis - mites seen as tiny pink or red shiny dots. Move faster than prey. Eat both adults and young prey.
  • Mealybug Predator - Cryptolaemus montrouzieri - an orange and black tropical ladybird. Larvae are white and spikey and almost invisible amongst their prey.
  • Thrips predator - Amblyseius cucumeris - a light brown or pink mite which attacks thrips larvae.
  • Caterpillar - Bacillus thuringiensis - a bacteria supplied as an insecticide which enters the caterpillar via sprayed leaves.

Beneficial insects which will come in from the garden and should be encouraged are bees, for pollination especially if you have citrus trees, ladybirds, lacewings, anthocorid bugs, hoverflies, centipedes, ground beetles, including black ones. These will eat and attack enemies such as aphids, scale insects, and red spider mites, as well as soil pests such as wireworms, eelworms, millipedes, leatherjackets and slugs and snails. Daddy Longlegs should be picked off whenever seen; their progeny are leatherjackets which have a voracious appetite for the roots of plants. You can be selective about caterpillars, and unless they are doing a lot of harm or they are Cabbage Whites, leave them for the sake of conservation.


Always spray in the late evening when bees and other friendly insects have retired to bed and treated leaves will not be scorched by the sun.

The safest insecticides on the market are soft-soap based. Soft soap was used by Victorian gardeners and until the arrival of chemical insecticides. All other insecticides used should, whenever possible be as narrowly specific to an individual pest as possible, and only used on the plant which is being attacked. Systemic insecticides, which enter the plant’s system and are sucked out by the pest in the sap, rather than those which kill by contact, are safest for bees, etc.

Glue traps, which are small sheets of yellow plastic covered in a sticky substance and which act like flypapers, catch a certain number of insects both friends and foes, as do butcher shop type electrical traps with a blue light. The yellow traps are useful in detecting when an infestation is impending, and should be used only until the introduction of any of the flying biological controls when they should be removed to avoid catching the beneficial insects.

There are now a few pesticides which can be used carefully alongside Biological Control predators and parasites: e.g. Rapid (specifically against Aphids); Pyrethrum based sprays; fatty acid (soft soap) sprays (Safers or the ready mixed types). Other chemical sprays generally require a few weeks’ gap between spraying and introducing beneficial insects.

For more information please contact our Helpline at 01206 240466.

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