Watering and humidity

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Watering in the greenhouse is an essential activity about which there is much disagreement. Some plants prefer a constant moisture, while others are believed to prefer to become rather dry before being watered. In practice the majority will adapt fairly readily to any steady regime that does not keep them sodden or allow them to dry out enough to begin to wilt. It is, however, a golden rule when watering by hand either to give enough water to moisten all the soil in the pot or to refrain from watering at all. Clean rain water {except in very large industrial towns) is likely to be belter for the more delicate pot plants and may be essential for lime-hating plants if the mains water is very alkaline. It is also an advantage if water can stand in the greenhouse before use in cold weather to take the chill off. However, tap water coming under pressure is highly charged with oxygen which is bénéficiai and static tanks easily become polluted. It is not always understood that air penetrates between the soil particles and that it is essential to all but bog plants that it should. If water fills all the air spaces in the soil for long, most plants will suffer root damage.

livery beginner wants to know how often to water in terms of days and this is an unanswerable question. The rate at which the soil in a pot dries out is affected by sunshine, temperature, atmospheric moisture, type of compost, and how firmly it is packed. The nature and size of the plants and whether they are growing or resting are other factors, not to mention the material of which the pot is made. The advantage of hand watering is that it can be selective, and success must be based on observation.

Holidays and other absences from home are the bane of the greenhouse enthusiast, and now that automatic watering is so widely practised commercially every amateur should give it serious thought.

The word automatic is often applied very loosely to some watering aids, which depend on daily attention and merely require less skill and save time when looking after large numbers of plants. It is, of course, easier to explain to a helpful friend or neighbour that a tap should be turned on or a tank re-filied than describe the drinking habits of all the precious plants, but this is not automation!

There are two main types of watering system that can be fully automated. The first is capillary watering, by which pots standing on damp (capillary) matting or sand draw water From below by capillary attraction. The second method is to water the surface of the soil in each pot by means of an individual nozzle or tube. Such trickle and drip systems need electricity if they are to be truly automated, whereas capillary systems need only a source of water.

It is difficult to give simple general advice about automatic watering, because conditions in each greenhouse and the collection of plants grown vary enormously. Even when a watering method is chosen, the interests and aptitudes of the gardener will affect the result, as in all gardening. Temperatures maintained in winter and the method of heating will also alter the climatic conditions in which the watering takes place. Nevertheless, a general understanding of the principles involved and the equipment available is essential, if the best use is to be made of it. Unfortunately all research is done for commercial interests and the equipment offered to the amateur is mostly marketed by very small firms, who are keener to produce something new than a system of lasting benefit.

Those specialising in a single kind of plant or crop are faced with the limited problem of its season of growth and rest, but most amateurs grow a mixed collection of plants in pots as well as raising seedlings in spring.

The average small greenhouse tends to be too hot in summer, poorly ventilated, and with too dry an atmosphere. All forms of automatic watering are likely to improve these conditions, and capillary benches, which add moisture to the air and accommodate the largest number of plants in the smallest area, are particularly suitable.

In winter the problems are different. In many greenhouses a combination of low temperatures with a damp atmosphere and poor air circulation encourages troubles such as botrytis, and unnecessary dampness is to be avoided. As better air circulation is achieved with slatted benches, it would be ideal if each pot stood well clear of its neighbours and was watered individually according to its needs.

In commercial glasshouses plants do well with individual drip watering to well-spaced pots on wiremesh benches. In a small private greenhouse or conservatory space is limited and appearance often cannot be sacrificed to technology.


The capillary bench is in many ways the most easily controlled and satisfactory method of automatic watering. In the early days sand benches were constructed where the pots stood on damp sand which was 2 inches above the water-level (5cm). Commercially this system was not very successful and it never caught on with the general public. In commerce there was too much trouble with the spread of disease. Personally I have used sand benches for fifteen years and prefer them in spite of a certain amount of trouble with worms and moss. The valuable aspect of this system is that each pot plant standing on damp sand absorbs from below, by capillary attraction, only the amount of water it uses. So long as the bench has a controlled and constant water level, sudden changes in the weather and the water needs of the plants are catered for. As there is never a shortage of water, the plants grow steadily and fast.

There is a limit to the height of the pot that can be used when watering by this method. The capillary attraction only carries the water up about 5 in. (12.5cm) when the water level is held 1.5 to 2 in. (5cm) below the surface of the sand, which has been found to be the most satisfactory arrangement for most plants. Pots up to 6 in. (15cm) high are satisfactory on capillary benches: larger pots are better watered from the top. For a really reliable and effective capillary bench, it is necessary for it to be level (± J inch) and to have a controlled and constant water level. It is possible to cover capillary benches with plastic sheeting with a hole for each pot if one is seriously concerned to reduce atmospheric humidity, but I have never found any need for this. Plants that need to be kept dry when resting are, of course, removed from the bench.

On all forms of capillary bench there must be direct contact between the damp surface of the bench and the compost in the pots. This means that there is no drainage material in the bottom of the pots. Modern plastic pots do not need this anyway. If clay pots are used, a small piece of glass-fibre insulating material can be inserted into the drainage hole to act as a wick. To establish capillarity, pots put on the bench are pressed firmly on to the sand with a slight twisting action, in hot weather if there is any doubt whether capillarity has been achieved, water once from above.

The compost used on all kinds of capillary bench must be well aerated if the plants are to thrive. This means that all potting is done very lightly - just a tap on the bench and a very light firming with the fingers around the edge when re-potting, but no hard ramming. The expert grower of exhibition plants may complain that this is not the way to grow a fine hardwooded plant, and he may be right, All I can say is that a mass of healthy and attractive plants can be grown with ease and success. Opinions differ as to what modifications to make to the compost for plants on capillary benches. I use John Innes composts with a little additional coarse grit or sand. J have also used soilless composts and mixtures of peat and loam-based compost. The one essential is to avoid consolidating the compost and to re-pot if a plant looks sickly for no apparent reason. It is wise to keep newly potted plants off the bench for two or three days, as those with damaged roots do not take kindly to this form of watering.

The capillary watering kits sold to amateurs are usually designed for use with capillary matting and many are only used at holiday lime. Capillary matting is rather ugly and needs fairly frequent renewal, but it can be made to work well, ft is essential to test the system thoroughly before a holiday as. if things go wrong, the matting dries very quickly. Various forms of float valve are used to control the water level.

For a home-made capillary bench all that is required is a level bench that is strong enough to support a couple of inches of wet sand and the pots without sagging. A solid edge to the staging is also desirable, and the whole is made waterproof with a single sheet of medium or heavy quality plastic sheeting.

The water level can be controlled in various ways. The ordinary domestic ball-cock is a rather rough instrument for making a sensitive response to very small demands for water. There are small plastic floats as used in the self-filling individual drinking bowls designed for cattle. These do not need mains-water pressure to work and the amateur plumber can fit them up. If benches are of differing heights, each level will need a separate water control consisting of one of these floats in a plastic box with a plastic tube from the water supply and another to the bottom of

A group of calceolarias (sec page 40|.

the bench. A tiny hole can be made in the plastic sheeting at the base of the bench and small black plastic tubing pushed gently through it, to give a waterproof joint.

Do not use transparent plastic piping as algae will grow inside it and block it in hot weather. Light coloured tanks are also a mistake. Algae will also grow on the matting. This does not matter but is ugly. The matting can be washed or treated with chemicals.

In time algae and moss will grow on the sand, and chemicals are sometimes used to prevent this. I prefer to scrape off and replace the surface of the sand occasionally and one can also wash and replace all the sand. Obtaining coarse sand in quantities of more than 7lb and less than a lorry load is the main difficulty with this system.

With capillary watering, no matter what equipment is used, one does want to be able to see at a glance whether the apparatus is working. When buying any automated equipment always ask the question: 'How do I see instantly if this system has stopped working?'


I fit is impossible to achieve a really level surface, one can have an irrigated capillary bench. This consists of a sand-covered bench which is kept watered but is not waterproof at the edges, so that surplus water drains away. A capillary mat can also be used in this way. it is merely a way of adding to the humidity and lessening the individual watering. Capillarity is easily lost in hot weather and it does not have the reliability or usefulness of the controlled capillary bench.


There are a number of watering systems that bring water to each plant, either trickling out of adjustable nozzles or dripping from fine tubing. With these the plants may be potted in the traditional ways and the pots can stand on any freely draining staging. Trickle lines and seep-hose can also be used to water plants growing in the ground and to keep irrigated benches moist. When used on the ground a point to remember is that, although long periods of watering penetrate more deeply, a wider area of soil is dampened by more frequent watering for shorter periods.

There are a variety of drip-watering arrangements using very small-bore plastic tubing with individual tubes to each pot; these are supplied by larger-bore rigid tubing. They can have adjustable rates of drip for different plants and positions, and can be tailored to suit any pot arrangement, although an artistic arrangement of plants is made more difficult. With fine tubing the trouble to watch for is blockage of small tubes from lime in the water. These systems are often activated by turning on a tap for a time each day. To automate drip systems, high-pressure water and also electricity are desirable, but amateur kits are available using a simple syphon system, in these, water drips slowly into a small tank, which, when full, empties through ihe trickle or drip lines connected to it. The disadvantage of this system is that a slow drip, if left unattended for long, is apt to stop completely, while a rapid drip will give too much water,

A sophisticated system using an electric solar control, which adjusts the watering according to the weather, is available for controlling either watering or mist propagation but this is a costly solution.

Perhaps the most obvious way to water plants automatically is to imitate rain, and this is done through nozzles of a similar type to those used for mist propagation. All effective systems of this kind need a source of water at mains pressure or a special pump. In hard water districts continual spraying will leave an ugly lime deposit on both plants and greenhouse glass which is difficult to remove. Where plants needing high humidity are grown, automatic spraying may be used for damping down the floor.

Those who want to specialise in lime-hating plants in districts with very alkaline water must remember that, unless they have ample supplies of rain water, or are prepared for the considerable cost of treating the water, their plants may suffer on an automated watering system.

The more elaborate automatic watering schemes use electricity. If both water and electricity are available, there is virtually no watering problem that cannot be solved at a price. The simplest arrangement that works reliably in one's own circumstances is usually the best. One thing to bear in mind is that there is no equipment for controlling the flow of water on a small scale which it is beyond the wit of ordinary people to understand. What is happening may be boxed in or obscured by technical terms, but it is bound to be based on some fairly simple principle. This can be understood and will be explained to those determined to know. Watering arrangements once installed must remain in working order for long periods, and it is virtually impossible to keep equipment working continuously if one does not understand it. Before installing anything that might need professional servicing, it is wise to check whether this is available as weli as its likely cost.

Several methods of adjusting the frequency of watering to the weather have been used with varying success. A time clock can be altered to match the season and can operate on a less than daily basis in winter, but it takes no account of whether the sun is shining or not. A solar control using a photo-electric cell has been used with success for some years. It needs to be fixed facing due south and is then activated by the amount of light falling on it. This does not necessarily match up precisely to the amount of water needed, but it is adjustable.

To turn water on and off solenoid (magnetic) valves have long been used, together with a time clock or other electronic controller. A daily watering of not less than 15 or 20 minutes can he arranged by using an ordinary time clock (as used in domestic centra! heating systems) together with a solenoid valve. If a very short watering time is needed, it becomes more complicated and expensive because a second time clock is necessary. The first (24 hour) time clock is set to come on for 1 hour a day and to switch on a second (1 hour) time clock which may be set for as little as 2 or 3 minutes. All this can work off mains electricity, but as it is considered safer in greenhouses to use low voltages, the electronic controllers designed for horticultural use usually have a transformer and work at 24 volts. These are linked to low-voltage solenoid valves. It is possible to have solenoids for all the various couplings of high and low voltage and water pressure, but one must be sure of what is needed. Obviously it is possible to bring Hie silicon chip into play and the day may soon come when the happy gardener presses a few keys by the bedside to activate all systems.

Many of us as children have watched the sluicing down of paths and the spraying of foliage in some large public or private greenhouse. Indeed the warm green smell of damp soil and the mingled scents of growing plants is what the words greenhouse and conservatory conjure up in our minds. This is the good growing atmosphere gardeners talk about. The amount of moisture in the air. and hence coolness in warm weather, is much influenced by the amount of green growth within the greenhouse or conservatory. If there is a concrete floor and a few rather dry pot plants, the temperature will rise very rapidly and the air will be far too dry.

The lavish use of hoses is hardly appropriate in the small greenhouse, but in summer there is a great need to increase the humidity in the air as well as to cool it. Some compromise needs to be made between what is desirable and what is practical. Spraying the floor morning and evening in the summer months is one way out, but the effect is not lasting in hot sunny weather and a more frequent automated spraying would be better. For orchids an electric humidifier is sometimes used if the plants warrant this

Dendrobium nobi/e, an epiphytic orchid suitable for the warm greenhouse.

luxury. For many plants, shade as well as humidity will be necessary, particularly if the ventilation is poor.

From October to March no extra dampness is needed, and in cool conditions the less water that is splashed about the better. In winter, hand watering should be done early in the day. The human senses are adept at judging atmospheric humidity once they know what is wanted. People tend to feel uncomfortable when the humidity falls below 50%, and this is too dry for plants. A daytime atmospheric humidity around 60 to 65% seems to be satisfactory for most plants. The humidity at night will be and should be higher.

Although mist propagation is not strictly what is meant by watering, I mention it here because it is a useful tool for those who have to be away a great deal. As well as rooting the more difficult cuttings, seeds can be raised to the pricking out stage under mist, and the plants then put on capillary benches.

In mist propagation various forms of so-called 'electronic leaf are used to control the amount of misting. Perhaps the simplest of these is the one directly linked with the actual conditions of humidity. In this the weight of water failing as mist turns off the system, until the plastic foam sponge which has absorbed the water dries out enough to alter a weight balance and thus turns on the mist once more. The other electronic leaves depend on water connecting electrodes and then breaking the current as they dry out. These may need frequent cleaning if the water is limy. A good alternative is the solar control already described.

Soils and feeding

A simple way to start growing pot plants is to buy a bag of ready-made compost and use it straight from the bag. Today, the choice is bewildering and ever changing, as the combination of research and marketing soon establishes new composts if they prove useful in nursery practice. These are mainly for the production of young plants, which is also what many amateurs are engaged in. However, the more permanent or specimen pot plant still responds to a traditional diet and each one of us will adhere to methods found successful in our own conditions.

Until some forty years ago every keen gardener took pride in his own special mixtures of the stock ingredients and often varied the compost for each species. Then the John Innes Horticultural Institution produced a formula which gave a satisfactory soil-based compost with slight variations for seedlings and more established plants. They were called the John Innes composts, and the problem of what soil to use seemed to have been solved. These composts are still sold in great quantities and preferred by many people.

Good John Innes compost is as good as it ever was, but unfortunately it becomes rarer every day. The composts are based on a medium loam soil, which only exists in a limited area of the country and is in very short supply. Before being used for potting, turves from good pasture are supposed to be stacked for some months with an even scarcer commodity, strawy manure, and then the whole heap mixed together and screened before being sterilised. Quite apart from the labour involved, the cost of transporting such heavy materials from one part of the country to another has become uneconomic. The result is that much of the John Innes compost sold is made with unsuitable soil. It may also be difficult to find suitable loam to make up one's own compost. However, if the soil is going to be less than ideal anyway, the home-made compost may be preferable for those who have the time and inclination to prepare it.

The loam should pass through a § inch (6-7mm) sieve and must be sterilised. This means bringing it up to a temperature of 200°F (93°C), and maintaining it there for twenty minutes either in a special steriliser or a saucepan over hot water.

To make John Innes seed compost, 2 parts loam, 1 part granulated peat and 1 part coarse sand (all by bulk) are mixed together, with the addition of 1J 02. (40gJ superphosphate of lime and J oz, (20g) of either finely ground chalk or limestone. These ingredients need thorough mixing.

The proportions for making john Innes potting composts are 7 parts loam, 3 parts peat and 2 parts sand. To this is added 4 02. (115g) John Innes Base Fertilizer per bushel for the No. 1 compost, 8 oz. (225g) per bushel for No. 2, and 12 oz. [340gJ for No. 3. Ground chalk or limestone is also added to the potting soils at the rate of | oz. (20g) per bushel for No. 1 compost (for very young plants), oz. (40g) for the No. 2 compost (for most plants), and 3 oz. (85g) for the No. 3 compost (which is needed for strong growing plants in large pots or tubs).

There are now some ready-made composts which are of the john Innes type but use modern slow-release fertilizers. These are sometimes in a separate sachet which enables the compost to be stored for longer without deteriorating. All loam-based composts are best used fresh. Another development is the substitution of perlite for the coarse grit or sand in the traditional mixtures. This may not be better but is certainly lighter in weight, which can be important.

A point the manufacturers seem to have overlooked is that keen gardeners like to experiment and mix their own composts. This may upset the scientist's careful formulae, but many amateurs mix ready-made soil-based and soilless composts together, A half and half mixture is popular and goes some way towards correcting the tendency of plants in peat to become top-heavy.

During the last twenty years there has been a steady increase in the use of peat-based composts. A peat and vermiculite mixture is also used, and more recently the all-peat and perlite composts have been developed. None of these have to be sterilised and they can be stored without changing their character, unlike soil

It is an advantage of the manufactured composts, or substrates as they are sometimes called, that they are lighter in weight and more uniform than anything containing soil. Nevertheless, they are not suitable for large specimen plants and the watering technique is different from that in soil-based composts. Peat holds more water than soil but dries out more quickly, and once dry may be difficult to wet. All the same most bought pot plants are in some type of peat compost and their care is familiar to many. As the distribution of the various composts is not evenly spread over the country, amateurs need to become accustomed to one or more that are readily available locally. Pine bark and plastic waste are other materials used in some composts.

It is important to remember that plants grown in soilless composts need supplementary feeding sooner than those grown in soil-based composts, as they do not have the natural reserve of plant nutrients found in soil. The modern slow-release and chelated fertilizers are suited to peat and sand composts and have often been included in their composition.

A potting shed can be regarded either as a necessity or a luxury depending on circumstances; but obviously it is undesirable to store composts, fertilizers, pesticides or unwashed pots in the greenhouse. Where there are children, a locked cupboard for pesticides and herbicides, away from heat, frost or food, is much more important than a potting shed.

However, potting must be done and is more likely to be done successfully and at the right time if it can be done in reasonable comfort. Although there is little room to do potting in the average greenhouse, this is a bad habit that I cherish. It is warmer for both plants and people and with a portable potting bench or even a bucket of compost it is perfectly feasible. Nevertheless, a well-stocked potting shed is desirable and a well-kept one a positive pleasure.

The basic ingredients of all potting composts have been loam, sand, leafmould and well-rotted manure. Each of these is a variable substance, and it is only with experience that one comes to know the feel of a compost that is porous and open, and yet with sufficient humus to retain moisture and nutrition and to support healthy growth. Both the plants grown and the watering methods determine the most effective compost.

The choice of materials is also influenced by the beliefs of the gardener. The compost used by the growing number of people determined to use nothing but wholly organic ingredients will be different from that chosen by those who find the development of slow-release chemical fertilizers an inspiring breakthrough. The ornamental plants in our homes can live on pills and substrates and artificial light, or they can even take part in a movement back to nature whereby the wastes of men are re-cycled for plant use. I will describe both fashionable and unfashionable materials for composts.

Loam. Fibrous loam, the basis of all traditional potting mixtures, is not just garden soil but the top 4 or 5 in. (10-12.5cm) of well grazed pasture, which has been stacked for a year until the grass has rotted, leaving the fibrous soil. For making John Innes composts it is suggested that a 2 in. (5cm) layer of manure should be spread on every second layer of turves with a sprinkling of ground limestone on the alternate layers. The whole heap should be thoroughly wet right through and is then protected from heavy rain and left to rot down.

Lea/mould. This vital ingredient went out of fashion and was replaced by peat; nevertheless the most dedicated gardeners have never abandoned leafmould if they have a source of supply. It is the product of the decay of leaves of deciduous trees, preferably beech and oak. If collected in autumn and turned once or twice, they break down in about eighteen months into a light fluffy substance that can be passed through a half-inch sieve. If just left lying in a wired enclosure, leaves usually take two years to decay sufficiently. It must be remembered that there will be lime in leaf-mould from trees on limy soil. Lime-free leafmould is a useful potting material for lime-hating and shrubby plants.

  1. For potting composts granular sphagnum or sedge peat without too much dust or small particles is best. Peat does not contain plant food.
  2. Sand should be coarse, clean and lime-free. Soft yellow builder's sand is not suitable for potting, nor is sea sand unless very thoroughly washed to remove salt. The sand particles should be up to J inch size (3 mm).
  3. This substance is extremely light and absorbent. In a granulated form mixed with peat and fertilizers it forms one of the commercial composts. It is also available as a sterile medium without nutrients. Cuttings can be rooted in it or in a mixture of peat and vermicuiite. it is so light that young plants can be lifted from it without damaging the finest roots.
  4. This is also a light and absorbent substance created by the heat treatment of volcanic rock. It can be used in a similar manner to vermicuiite and is also used in orchid composts, sometimes being substituted for the grit or sand in John fnnes type composts. It is available in a variety of granule sizes for different purposes.

Garden compost. The compost heap of decayed vegetable matter is a valuable source of humus with a nutrient value that will vary according to how well it is made. For potting it needs to be very well made, if it is not to be full of weed seeds and harmful organisms.

A compost heap should have a well aerated base of coarse material such as twigs. On this 6 in. layers (15cm) of vegetable matter (excluding woody stalks and seeding weeds) are interspersed with 2 in, layers (5cm) of animal manure, if possible, or a good sprinkling of any organic manures of animal origin, such as dried blood, fish manure or hoof and horn. Following this comes a sprinkling of earth mixed with wood ashes and lime, or lime alone. These three layers are repeated until the heap is completed. To heat up properly, it needs to be about 6ft by 4ft (1.8 x 1.2 m) in area and not more than 5 or 6 ft high (1.5 or 1.8m), For small heaps a compost box or bin is helpful. Lawn mowings and fallen leaves, which tend to matt together into a slimy mass, should only be added in thin layers or mixed with other refuse. Comfrey plants are sometimes grown to provide extra green material to rot down. If animal manures are lacking, there are both natural and chemical activators which can be added to hasten decomposition. The whole heap needs to be moist but not sodden, and a ventilation hole made with a crowbar in the centre is a good idea. The compost should reach a high temperature during decomposition and be reduced to a dark brown sweet-smelling earth. If it dries out or cools down at an early stage, this will not be achieved.

Wood ashes. These should be kept dry until used. They are an organic source of potash and are sometimes added to composts, particularly if the soil is heavy.

  1. Lime is not a fertilizer in the usual sense, although it supplies calcium which many piants need. It improves the texture of clay soils and corrects acidity, but it should not be applied to soil with a pH of 6.5 or above (pH is a measure of acidity). The neutral point is pH 7.0, Above is alkaline and below acid, A pH of 6.3 is considered best for John Innes compost and pH 5.3 to 5,5 for peat and sand composts. For lime-hating plants the pH needs to be below 6.0. One can discover the pH of the soil with a simple soil testing outfit. One can also ignore the whole thing and hope it is all right!
  2. Cow manure is perhaps the most generally satisfactory for horticultural purposes, if obtainable, but horse manure is good for heating up a slow compost heap. Poultry manure is chemically rich unless it has been spoilt by exposure to the weather. It should be stored dry under cover. No manure should be used in a greenhouse border until it is in a well-rotted state, but fresh manure may be added to the compost heap.

Fish meal. This is an organic source of nitrogen, phosphorus and potash and is a useful fertilizer for the greenhouse border.

Bonemeal. This slow-acting fertilizer, containing phosphorus and a little nitrogen, suffered an eclipse owing to the fear of its transmitting disease, but is now always heat treated.

Poinsettias [Euphorbia puJcherrima) are popular plants at Christmas time (see page 56).

When plants are growing strongly and the pots are full of roots, the question of additional feeding arises. Some understanding of the processes of plant growth is helpful. We all realise that air, water, light and sufficient warmth must be supplied for growth to take place. Then the leaves will be able to manufacture sugars, starches and proteins, while the roots obtain the various essential minerals and moisture from the soil. Nitrogen, phosphates and potassium, sometimes cryptically referred to as NPK, are the most used and most likely to need replacement. They are present in various proportions in all the compound fertilizers and liquid feeds. Those designed for foliage plants will have more nitrogen, whereas those intended for quick growing flowering plants will have more phosphates and those for tomatoes more potassium. A tomato fertilizer is a convenient source of potash for the occasional feeding of most plants. A frequent error of amateurs is to confine themselves to one liquid feed meant for foliage house plants and then to be amazed when flowering is disappointing.

The precise and detailed needs of many plants are not known, and until recently the essential trace elements found in natural soils could not be included in fertilizers or composts. Now the dedicated gardener can use slow-release fertilizers and many trace elements fused into microscopic glass pellets, and these are even to be found in some commercial composts. Another possibility is the foliar feed whereby plants absorb nutrients through their leaves when sprayed with the diluted feed. This is a quick pick-me-up when things have gone wrong.

The secret of feeding is to give little and often and never more than is suggested on the packet. Plants that are resting do not need feeding. The re-potting of a sickly or seriously pot-bound plant will do far more good than feeding, and, if the roots are decayed or being attacked by some pest, feeding will not help.

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