By definition a houseplant should grow and thrive in a house, and with a little care most will do so for many years. But it must be remembered that the home is a very alien environment for plants, far removed from the tropical rain forests of South America, the arid deserts of Mexico or Arizona, or many other parts of the world from which our house plants originally came. Even if we keep our homes warm they lack the natural humidity and light that most exotic plants require, and it is these two factors that prevent many good greenhouse plants being grown in the home for long periods. It is impossible to match natural conditions. and our efforts must inevitably be aimed at a compromise. This is not always a bad thing, for we don’t want our rubber plants as high as a house or cacti as tall as a man – sizes which they might achieve in the wild. If a greenhouse or a conservatory is available, many houseplants will benefit from a spell in these more amenable conditions from time to time – but that is no substitute for providing the best conditions within the home. Light, temperature and humidity are all important. but compost, feeding and watering are equally vital and due regard must be paid to all of them if you want healthy and thriving plants.


Compost does more than anchor the plant – it holds reserves of food and moisture and keeps the roots aerated. It is also host to many micro-organisms, some of which are beneficial.

Compost is not essential – hydroponic units use only water and fertilizers and an inert aggregate – but this is a specialized method of growing plants and it has taken many years of laboratory research to reach the stage where we can easily achieve with water and chemicals what the soil does naturally. Even then it would be totally wrong to suggest that all plants can be grown successfully in nutrient solutions. For the vast majority of houseplants, a good compost is essential, and the choice will lie between a traditional loam-based type or one of the peat-based composts. There is much to be said for each kind. and it is likely that both will continue to be used.

Loam-based composts are best made to the John Innes formula. This is not a proprietary compost and anyone can make it. though the amateur is advised to buy it ready mixed. The main ingredient is good quality sterilized loam, which gives the compost substance and weight (important for plants with heavy top growth, which may become unstable in a light compost). It is also less prone to dry out so completely and as rapidly as a peat compost, and there is a better reservoir of plant food. And because it has been sterilized, harmful organisms have been removed. Most plants will grow equally well in John Innes compost or a loamless type, but a few plants such as the shrimp plant (Beloperone guttata) seem to prefer the John Innes mixture. Peat-based composts are light and pleasant to handle, and for plants such as African violets (Saintpaulia ioitmiilui) are

a superior growing medium. Their drawback is that plants set in them need feeding sooner after potting than would be the case with John Innes. and watering is more difficult to control accurately. The compost can dry out suddenly. and be difficult to moisten thoroughly. Also, it is less easy to judge visually whether the compost is in need of water, and more emphasis must be placed on weight,. Large plants may topple when they become heavy, and for plants of some stature a loam-based compost is best. Provided they are watered and fed properly. however, peat composts can produce extremely gratifying results. No matter how useful standardized composts are. there will always be the need for special mixtures for particular groups of plants – bromeliads, orchids, and lime-hating plants all have their particular needs. Where a particular compost is required this will he explained but where no special mention is made it- can be assumed that either John Innes or a peat-based compost will be suitable.

Potting on

Never be in too much of a hurry to pot on a plant into a larger container. Growing plants indoors has to be a compromise between providing the roots with sufficient soil and nutrients and the need to avoid root disturbance. No plant appreciates having its roots unsettled, and any damage to them will result in some check to growth.

Never repot a houseplant merely as a matter of routine – say on an annual

basis. Some plants may require potting on annually, but many others will not and to do so could affect dowering. Be guided by the specific information in the A-Z of Houseplants , and by the state of the roots. If the pot is full of roots (you can check this by inverting the pot. supporting the plant. and giving it a sharp tap on a hard edge to release the soil-ball), and they are coming through the drainage holes in the bottom of the pot. then repotting is probably necessary.

Don’t be misled by a few fibrous roots coming through the drainage holes. however. If the plants have been grown on a capillary bench or mat – the roots are naturally attracted to the source of water. And it is quite normal for some roots to run round the side of the pot -only if there is a solid mass of roots will it qualify for potting on. A ’cv plants need very little soil -bromeliads. for instance, use their roots principally for anchorage. Some plants do not have an extensive root run and are best grown in half-pots instead of pots – cacti are typical of this group. Half-pots have the diameter of conventional pots but not the depth. Plants in 7.5cm (3in) pots are normally potted on into 12.5cm (5in) size, and from that size to 15cm (6in) pots, and so on in 2.5cm (1 in) increments. To repot a plant, either use the technique illustrated on the right, or use the method described below. Both methods produce equally satisfactory results. Start by placing a piece of broken pot over the drainage hole of a clay pot. or just fibrous material such as peat over the base of a plastic pot (always avoid crocks if capillary mats are to be used). Place a little dampened compost over the base material, then insert the existing pot (or empty one of the same size) inside the larger one. ensuring the level of the soil surface will be about 12-25mm (j-lin) below the top of the new pot when filled. Pack compost firmly between the inner and outer pot. so that it leaves a mould when the inner pot is removed.

Always use the same type of compost as that in the existing pot. ensuring that both it and the soil-ball are uniformly damp – not dust-dry. but not too wet. Knock the plant out of the old pot by tapping it sharply on a hard surface while supporting the plant. The root-ball will Ht snugly into the depression in the new pot and compost, and it can be firmed into place with a further sprinkling of compost. Firm well using the fingers or a suitable piece of wood. Finally, water well and keep out of full sun for a few days.


Give your plants the right compost. temperature and light, water them regularly, and they will survive. But it is proper feeding that makes the difference between a plant that just survives and one that thrives. Never underestimate the importance of feeding your house-plants. for it can make a tremendous difference to their well-being. It is best to use a special houseplant fertilizer, not because their requirements are very different from those of most outdoor plants, but because the dilution rate is more practical for home use – a few drops to a pint (litre) perhaps.

Most loam-based composts will contain sufficient reserve of the minor or ‘trace’ elements such as boron, molybdenum and copper, to make it unnecessary to worry about these – but plants in pots soon run short of the three major plant foods: nitrogen, phosphates and potash. These will be found in adequate proportions in all houseplant foods or in a good general fertilizer.

Whether you use a liquid concentrate or a soluble powder makes lit tie difference to the plants, but for say a pint of diluted fertilizer a liquid is probably best as it is difficult to measure the powders accurately at this level: but if you are likely

to use about 5 litres (1 gallon) or more at a time, it could be as easy to use a soluble powder and there could be savings if you choose one that can be used for the garden too so you can buy a large size. There is little merit in using foliar feeds as it usually means the plants have to be moved to a place where overhead spraying is not likely to wet furnishings. Fertilizer tablets have the merit of being easy to apply (just press into the compost). but are not the best method if a capillary system of watering is adopted.

When to feed

Feed regularly during the active growing season – every week or fortnight (be guided by the manufacturer’s instructions). Feed only infrequently (perhaps once a month) if a plant is growing during the winter, but not at all during a resting period. Obviously plants vary in this respect – and although feeding is best done on a regular basis it should not be undertaken according to the calendar regardless of the state of the plant. As a general guide, most plants will need feeding from late spring until autumn. Plants that make a lot of growth may need more than those of more restrained habit. Bromeliads and cacti do not need much food, and in the case of most bromeliads it is necessary to apply it to the central vase. Most plants will ncct feeding when you buy them – the food reserves in the compost are not great and if established and well-rooted plants are purchased they will probably be ready for supplementary feeding.

Feat composts in particular can run short of plant food quite suddenly. Although they have a long-life fertilizer added when they are made, they lack the natural reserves possessed by loam. Plants growing in a hydroculture unit will require feeding about every six months, if an ion-exchange fertilizer is used.


Probably more houseplants are lost through errors in watering than from any other cause. And ironically, it is usually too much rather than too little water that causes the problem. Unlike plants growing outdoors with a large reservoir of soil, houseplants have very little ability to withstand extremes of drought or waterlogging. There is usually no ultimate soakaway for the water, and any surplus simply sits in the saucer and the compost remains waterlogged unless there is a suitable gap. Conversely, because of the small volume of compost in a pot. it tends to dry out quickly in warm weather: clay pots are

more prone to this than plastic pots. And though most plants will wilt – even drop a few leaves as a natural way to conserve moisture and reduce water loss through transpiration – they will normally revive. But there comes a point of no return for any plant, and to leave them unattended for more than a week in warm weather is inviting losses. The ability to judge when a plant needs water is a combination of experience and observation.

The traditional way to determine when a clay pot requires water is to tap the outside with the knuckle or something like a cotton-reel on a stick. If the pot and soil-ball are dry the pot will produce a hollow ring, and the plant will need water; but if they are still moist the pot will produce a dull tone and no water should be given. The difference soon becomes obvious with a little practice. The knuckle method is line for one or two plants, but if you have a large number of pots it becomes a little hard on the skin, and an improvised ‘hammer’ is the best solution. Tapping only works with clay pots, and as most plants are sold in plastic containers nowadays it is most unlikely that it can ever be the complete answer. A rather laborious but very accurate method is to weigh the pot. By placing the plant on a spring scale when it requires water and weighing it again once the compost has been moistened sufficiently, the two weights can be noted. It is not unusual for the difference for a small plant in a peat-based compost to be about 50g (2oz). Once this has been done it is always possible to ascertain the moisture requirements of the compost (although as the plant grows it will be necessary to repeat the ‘before and after’ exercise occasionally). Unfortunately, life is not long enough to enable many plants to be watered in this way. but it can be useful for a ’cw plants that will not be likely to suffer damage as a result of regular handling for the weighing operation. Its greatest merit is as a means of providing the beginner with the necessary experience to judge the state of the compost by sight and

Regular watering, feeding and good humidity are necessary for healthy houseplants. The wick method is one way of watering while on holiday.

touch. After a few weeks of weighing, a natural judgement will be acquired and the need for such precise measurements will diminish.

It is possible to buy meters having a probe which is pushed into the compost to give a reading of the moisture level in the compost. They hardly look elegant sticking out of the compost, and constantly pushing the probe into the soil is likely to damage the roots. As an aid to learning to judge the visual signs, however. they can be useful. Unless one of the ‘automatic’ systems is used it is going to become necessary to learn to depend on judgement: and this has the advantage that it makes you observe the plants more closely. Most plants will tell you in no uncertain terms that they need water – by wilting. Bui that stage should never be reached –

it means you have failed to notice the more subtle indicators. The compost itself is the best guide, but never go by surface appearance alone: if you give it just a dribble of water the surface will appear moist, but the compost at root level could still be dry. Loam-based composts are the easiest to judge and to water. It will be clear from the lighter appearance of the surface that it is drying out, and it will be drier to the touch. Even so. discretion must be used – if the plant was only watered the previous day the chances are that only the surface has dried and the compost beneath may be damp. Do not be in too much of a hurry to water, as loam-based composts tend to dry out gradually. Peat-based composts are more difficult. They can dry out very rapidly once allowed to become too dry and when

that happens it is much more difficult to moisten them evenly again. Because the colour difference between moist compost and dry is less pronounced than it is with traditional composts, it is more difficult to determine when water is needed. But because dry peat is very light, the weight of the pot and plant is a good indicator (there is no need to place the pot on scales; the difference will be so marked that you will soon be able to judge). Never water by the calendar – if the weather and home environment were as predictable as the date there would be some merit in watering on a particular day of the week, but that is not the case. Also, some plants will need watering more frequently than others, and at certain times of the year most plants will require a resting period when they should be kept almost dry. This makes it

necessary to judge each plant on its merits before watering. There is something to be said for ‘watering days’, provided you do not water everything regardless of its needs. By watering on say Mondays and Thursdays. the plants are not likely to be forgotten and they will be inspected at least twice a week. It also makes feeding easier to remember – you can apply a suitable fertilizer perhaps every Monday, or every-other Monday, depending on recommendations, the plant, and the time of year.

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