How To Have Healthy And Happy House Plants

House plants are those plants that can be expected to spend all their life in a dwelling house.

If you have a greenhouse you can grow a very large number of plants for decorating your rooms. However, once they have spent a certain time indoors, they are then returned to the greenhouse and kept there to recover.

There is a difference between these and permanent house plants. These are not house plants in the sense in which we shall be discussing them.

Here we shall confine ourselves to plants that can be expected to thrive in the rather difficult conditions of a dwelling house.

Humidity Basic Requirements of House Plants

Conditions in rooms are difficult for plants mainly because the atmosphere is very dry. The majority of house plants are evergreens from tropical countries and in the tropics you are only liable to find evergreens where the atmosphere is damp. In many parts of the tropics the atmosphere tends to be so wet that a number of plants have evolved, known as Epiphytes, which can get all their nourishment from the atmosphere and have more or less dispensed with a root system. We do not want a moist atmosphere in our rooms, but it is possible to create a moist zone around our plants, by standing the pot or pots in some container, which will either contain water or will contain some substance such as peat, which can be kept moist.

You can put pebbles in a dish, nearly cover them with water and stand the pot on the pebbles, or you can get rather a deep bowl, plunge the pot in some moisture-retaining material, which can be peat, or sand or moss and keep this surround always rather moist. Both these methods will ensure that water vapour will always be rising around the plant and the warmer it is the more vapour will rise, which is just what the plant likes. If the pot is stood on pebbles you should make certain that the base of the pot is clear of water.


Compared to even a rather shady situation outside the light in rooms is not very satisfactory. It is, naturally, at its best on the window sill and gets down to near impossible conditions in corridors and halls. Some plants have evolved to grow in extremely poor light conditions, but it is only in the very densest forests that you will find the dark conditions of parts of our houses. Apart from a few ferns, not much will grow in these very shaded conditions and even these will not grow so well as they do where it is lighter. This means that the choice of plants for these murky places is extremely limited and it is probably easiest to forgo plants altogether in this sort of situation, rather than to put plants in and see them slowly deteriorate.

In reasonably lit situations, it is probable that the light will be coming from one direction only, unless you have a room with windows on all sides. Plants tend to grow towards the light, so if your plant is lit from one window only, turn it slightly every week, so that all parts of the plant will be illuminated in turn. This will not only ensure that all the leaves receive ample light (and without ample light the leaves will not function properly), but it will also mean that the plant stays symmetrical and does not grow twice as fast from the side nearest the light source. This should be done whether the plant is on the window sill or whether it is in the centre of the room.

Leaves and Roots

Most plants have two main feeding organs, the leaves and the roots. The leaves can take in plenty of nourishment and syringeing them with a foliar feed will have surprising results, but their main function is to make food for the plant. The roots will take up moisture and various chemicals from the soil. Normally neither can subsist without the other, but some plants do dispense with roots to a greater or lesser extent. A very few flowering plants dispense with leaves, but they can only do this by robbing other plants. Most plants require air, water and soil before they can function. Lir Apart from increasing the humidity of the air, there are other considerations. Draughts are appreciated by plants as little as they are by humans. A draught is a localized stream of cold air, which will attack a portion of the plant only. This will first cause the leaves to drop and may eventually kill the plant, so a very draughty situation should be avoided.

Fumes from various forms of heating are another problem. Paraffin oil burners are normally fairly innocuous, although a few plants will shed leaves if placed near them, but if something goes wrong and the appliance smokes, you may well find many of your house plants dying. The fumes from gas fires used to be harmful to many plants, but the fumes of modern natural gas do not seem to damage plants. Coal fires seem to be harmless and, of course, central heating which maintains a more or less even temperature, is the ideal.

Heat And Cold

In the open air it is a safe assumption that the temperature will be lower at night than during the daylight hours. If you are out at work all day, and you do not have central heating, you will not light your fires until you come home, so that you may get the appalling conditions, from the plant’s point of view, of a cold day and a hot evening. Many plants are very tolerant and can survive these unnatural conditions, but bear in mind that it is the daytime temperature that is the important figure to watch, as it is during the daylight hours that most of the growth is made.

The fact that your room at night may be at a temperature of 76 F (21°C) does not mean that you can grow the plants that require this temperature, if it is liable to fall to 45°F (9°C) at midday. Minimum winter temperatures refer to the daytime readings, and these may fall a few degrees at night without any harm being done, so that you can air the room at night without qualms. During very frosty weather plants that are on the window sills should be brought further into the room, as it is quite possible for the window panes to be freezing, even though the rest of the room is quite comfortable and frost will certainly damage any house plants on window sills and will probably kill them.

Apart from frost many plants from warm climates will survive at temperatures that are lower than they require to make growth. For example, the popular Philodendron scandens will go through the winter quite happily with the temperature as low as 45°F (9 C), but it will be in a state of suspended animation. Not until the temperature reaches 60°F (15°C) will it start to make any growth. The recommended winter temperatures for house plants are usually about 10 F (5 ½ C) below the growth temperature, which means that if they are adhered to the plant will survive perfectly well, but will not be making any growth. The point of this is that growth made during the short daylight hours of winter is usually not very decorative.

The stems are liable to become spindly and drawn, while the leaves will be small and a had colour. Indeed with foliage plants it is usual in the spring to nip out all the growing points and any bad growth that has been made in the ,winter, so that when the plant does start into growth again, the growth will be well-leaved and the plant will become bushy rather than drawn. Lowever, there are available enclosed glass boxes with their own heating and illumination and in these it is possible to keep tropical plants growing evenly throughout the year.

It is customary to put house plants into three categories: Cool, Intermediate and Warm.

  • The Cool group need a W inter temperature of from 45 F-50 F (7-10 C), while a few, notably Ivies and Fatshedera will tolerate even lower temperatures.
  • The Intermediate group need winter temperatures around 55 F (13 C)
  • The Warm group need a temperature around 65 -70 F (18-21 C). During the summer they will need at least to 10F (5 ½ C) more. Few people can manage to maintain the higher temperatures and plants needing them are not discussed here.


Nowadays one has a choice of two sorts of compost, those containing loam and those without loam, known as soilless composts. The most popular compost containing loam is the John Innes Potting compost, usually referred to as J.I.P. This is probably the best compost that one can purchase ready mixed. J.I.P. 1 is used for plants in 3-in. pots, J.I.P. 2 is used for plants ins-and 6-in. pots. For larger pots use J.I.P.3.

Good quality loam is hard to come by in large quantities and so the peat-based composts are now being increasingly used. These are mixtures of peat and sand with added chemicals. Peat and sand contain no nutrients so that when the plant has used all the chemicals in the soilless compost it will starve. With plants that are only going to he kept for a single season, fin example, Primula malacoides this does not matter, but with plants that are going to he grown on from year to year, it is necessary to start replacing the chemicals as soon as the plant starts to use those already there.


Most house plants make their main growth between the end of March and the middle of September and this is the time to replace the chemicals by some form of feeding. There are various proprietary feeds, all of equal value, but it is necessary to Mow the directions as to the amount and frequency of application. As the plant can take up only a limited amount at a time, little and often is better than large quantities at long intervals. Moron er any food not axailable to the plant is liable to be washed out during subsequent waterings, so it is not only potentially dangerous, but also wasteful to gixe too much food in any single application. Most of the feeds are applied to the soil dissolved in water and these should not be given when the plant is completely dry, otherwise the chemicals could damage the roots. Feeds are best applied about two days after the normal watering, when the soil will not be completely dry, hut equally will not be sodden. It is also possible to apply tnliar keds to the leaves, by syringeing the plant with a foliar feed solution. This is one of the best ways of feeding a plant, hut it may not be convenient to syringe plants in your rooms. It is, however, usually possible to remove all the plants to your draining board and syringe them there.


As the plants grow, so do their roots and after a time it is necessary. To move the plant to a larger pot. Most plants will want potting on yearly fur the first few years.

The usual progression is from a 3-in. pot into a 5-in, pot and thence into a 6-in., 7-in., and finally an 8-in., in which pot it will probably remain, as plants in larger pots tend to be very large and unwieldy. Usually once you reach the 6-in, pot, it will probably suffice to pot on only every other year, so that it will be six years before you reach the 8-in. Pot. Potting on should only be done when the plant is in full growth, so that May is usually the best month. If you tip the plant out of its pot (which is best done a day or so after watering) you can see if there are plenty of roots and if these are showing white tips. If the pot appears to be full of roots and these have their white growing tips, the plant is ready for potting on. This is best done when the plant is on the dry side, although it should not be dust dry, the soil may fall away from the roots when you take it out of its pot.

Take the plant out of its pot and lay it on the potting bench, or on the draining board. If you are using a loamy compost, put some coarse grit or broken crocks at the base of the new pot; with loamless composts this can be dispensed with. Now place some of the compost in the base of the pot and stand the old plant in the middle to see if you have enough in. In pots up to 3-in. There should be a gap of 1 in. between the soil level and the rim of the pot, while for larger pots the gap should be an inch. If the level is too high, you will not get all the soil moistened when you water, if it is too low, you will get too much water and also the plant will not have all the soil that it could have, so this is a matter worth paying attention to. When you have the right level, fill in around the old soil ball with the new compost, firming it down with your thumbs fairly heavily, otherwise you will find that after watering there will be a gap between the old soil ball and the new soil. The new soil you are using should be on the dry side and crumbly, hut not dust dry.

Once repotting has been completed, give the plant a good watering, after which it should be allowed to dry out and only watered sparingly for the next week or so. Putting the plant in a warmer situation will encourage the roots to grow more rapidly into the new soil. No feeding is necessary until this new soil has been occupied by fresh roots.


The most essential part in the successful growing of house plants is in the correct use of the water can and more plants are lost through drowning than through any other cause. When you do water, you should do it properly. Fill the pot to the brim. If you give less it may well not moisten the whole of the soil ball. It does no harm to make sure of this and to turn Out a plant a few hours after watering to see if the whole soil ball has been watered. If it has not, the only thing to do, if the plant is not in a state to be repotted, is to give two applications each time you water.

If you have some method of catching and keeping it, rain water is much to be preferred to tap water, but it is not always possible to obtain this. During the winter, very cold water will lower the temperature of the soil in the pot, perhaps to an excessive degree. Ideally the water should be at the same temperature as your room. You can get this either by mixing some hot water with the cold water, or by storing some water in your room for at least 24 hours before you use it. With most plants the temperature of the water is not very critical, but as far as African violets (saintpaulias), are concerned, if the temperature of the water is lower than 53°F (13 C) or higher than 60 F (15.5 C) you are liable to get unsightly blotches on the leaves.

Always, during cold weather particularly, avoid using very cold water, or water that is more than luke warm, otherwise you can again damage the roots. Having watered the plant, give it no more water until it has used up all the water you have applied. The smaller the pot, the sooner the soil will dry out, so that plants of the same species in 3-in. pots will require rewatering sooner than plants in 5-in. pots. Plastic pots, not being porous, retain water for longer than clay pots. During the spring and summer the plant will absorb water much more rapidly than during the autumn and winter, when growth is almost stationary and all the plant requires to do is to replace any water it may have lost through its leaves. It will lose more in high temperatures than in lower ones, so the room temperature in autumn and winter is also a factor.

There can be no hard and fast rules for watering plants, as, for example, once a week or once a fortnight, but if you inspect your plants daily, you will notice when the soil dries out. Soil at the top of the pot may well be dry while the lower portion is still reasonably moist, so wait for 24 hours after the top soil looks dry and then water. In this way there is little risk of overwatering.

If, when you water, the water runs straight through the pot and out at the bottom, the soil must have become over dry and shrunk. This can usually be cured by firming the soil around the edge of the pot with your thumbs, but if this is not effective fill a bucket with water to the level of the pot and stand the pot in this water and leave it there for 2 or 3 hours, then remove it and firm down around the edge of the pot. Mother-in-law’s tongue (Sansevieria trifasciata laurentii) is only watered once a month during the winter and this could well be excessively dried out when you want to give more water in the spring, so for this and similar plants the bucket treatment may be necessary.

Leaves wilting is usually a sign of a plant needing water, but it is not a certain sign. If a plant is dying as a result of overwatering, the leaves may well wilt, so that if you see wilting with a wet soil ball, you can be fairly sure that you have over-watered and that you must let the plant dry out (although your chances of getting it to recover are pretty slim). Also leaves may wilt if they are in burning sunlight. They will immediately recover if placed in the shade or if they are given a light spray with cool water and this phenomenon is, in any case, only temporary; the leaves wilt to prevent excessive lack of water. If the leaves are wilting, inspect the plant and if it is dry, then watering is the answer, but do not water wilting plants unless you have made sure that they are dry.

Cleaning Leaves

In towns and industrial districts, the air is liable to be polluted and some attention must be paid to the plant’s hygiene. The plant ‘breathes’ through its leaves and if these get clogged up with dust, the plant will not grow well. It is, therefore, advisable to sponge the leaves once a week. Use a piece of cotton wool and luke warm water, but sponge the mature leaves only, as the young leaves are very soft and could easily be damaged.

Pest Control

Insect pests are uncommon on house plants, but can be prevented from spreading by means of this weekly spongeing; even greenfly can be removed in this manner. Aerosol insecticides are available to deal with any serious infection, but these are often poisonous, so they should be kept away from children and the aerosol should not be applied in the house, but in the open air or in an outhouse or garage in inclement weather.


Many house plants have a stem from which side branches emerge. With such plants, it is usually good policy to remove the growing point, as well as any unsatisfactory winter-made growth in the spring. This is known as stopping. Stopping will encourage the production of sideshoots, so that you have a nice bushy plant as opposed to a rather thin lanky one. However, there is no use in stopping a plant unless it is well-rooted and making good growth. If it is not, all you will do is to get another growing point to replace the one you have removed and the plant will not bush out. With some very vigorous plants, such as the tradescantias, it may be necessary to stop two or three times during the growing season and sometimes with such plants not only the main growing point is removed, but the side shoots are also stopped when they have elongated sufficiently. Further details about whether or not to stop will be found under the descriptions of individual plants.


Some house plants can be easily propagated from tip cuttings in the home without any elaborate paraphernalia. For these you take a piece of the plant with the growing tip and some 2-4 in. of stem, depending on the ultimate size of the plant; low growing plants will not have much stem. Now make a clean cut with a razor blade at the lowest leaf joint. Then remove most of the lower leaves, if your cutting is very leafy, leaving only about a third of the leaves. Fill a small pot either with a ready purchased cutting compost (the soilless ones are very satisfactory) or with a mixture of equal parts (by bulk) of peat and sharp sand, and then insert your cuttings to a depth of about 1 in. Water them in and then enclose the pot in a polythene hag (or invert a large glass jar over the pot). The pot should be stood in a shady situation.

The best time to take cuttings is between mid-May and mid-August and the worst possible time is during the winter when rooting will probably not take place at all. Rooting usually takes place between 3 and 6 weeks after taking the cuttings. If you see new leaves being produced, that is a fairly reliable sign of rooting. Another method is to give a very

gentle tug to the cutting; if there is some resistance it is probably rooted, but if it just comes out, it must be reinserted and you must wait longer. Once the cuttings are rooted, remove the polythene bag or glass jar, and wait a week. Then knock the potful of cuttings out and pot each one up separately, taking care to damage the roots as little as possible. The newly potted-up plants should be put in a warm situation for a week or so and then they can be placed in their permanent situations. One or two plants require special treatment, but this is noted below. Some plants will root faster if the pot is placed in the airing cupboard – cuttings do not seem to mind being in darkness while they are making their roots, but once these are made, the cuttings must be brought out into the light and it is probably better to be patient and keep the pots outside.

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