Cultivation of indoor plants

From the descriptions of the many different indoor plants already given, it is evident that there are numbers of different aspects of cultivation and environment that have to be considered, if thriving plants are to be enjoyed. The time has now arrived to consider all of them on a practical plane.

Light
The fact is that human beings are able to keep more healthy, or at least they think they can, in less light than plants need. As a result, most places in our homes are not light enough to suit the well-being of many indoor plants. Thus, keeping house plants at their best under such conditions is not an easy task. To start with, it is important to get rid of one assumption that might appear to be logical, but is completely erroneous, and that is that any shortcomings in this respect can be overcome by giving the plants long spells in direct sunshine. With a few exceptions, plants object to being exposed directly to the rays of the sun.

Now those who are dedicated enthusiasts to growing house plants can overcome this difficulty by installing cabinets, racks of shelves, planteriums, all illuminated with fluorescent strip-lighting burning for long hours during the day. Some despise the altering strength of natural light during the day and create a completely independent environment for their house plants in a cellar, where the hours and intensity of light can be rigidly controlled.

Fortunately, the majority of us have house plants in our homes because they are pretty and add considerably to the interior decoration. There are, however, two important things that can be learnt from these house plant enthusiasts and the research work of the plant scientists, that provided them with their expert knowledge. These are, firstly, that the majority of house plants must have good light and secondly, that they appear to be as happy in artificial light as in sunlight. So important is the first point that emphasis is always given to those few plants that will tolerate poor lighting.

There are several things therefore that owners of house plants can do to meet the needs of their plants. The first is to put them always in the lightest place out of the sunshine in the room; secondly, move them as near the window as possible ; and thirdly, keep the curtains and blinds fully open as long as possible during the day. If house plants have to be put into a dark corner, make sure that fluorescent lighting is provided to supplement the natural light. Spotlights have proved very effective for this purpose. It must be remembered that a grouping of house plants in a dark corner of a room has no value as a decorative feature. So light it up.

Warmth
Throughout the book, the necessity of giving plants varying degrees of warmth has been continuously mentioned. Fortunately, in these days of central heating, the heat conditions in many houses is much more suitable for house plants than it was in former days. The big menace is fluctuations of temperature arising from fairly long periods early in the day when rooms are not heated much, then other periods when they might be overheated, followed by a rapid fall in the temperature during the night, perhaps even below freezing point. Such conditions are far more damaging for most plants than their being kept continuously in a steadily cool place. So in order to keep house plants healthy, put them in a position where the temperature is as uniform as possible. Always avoid, for example, standing them on the mantelpiece, where they might be roasted for part of the day, on the shelf over the radiator or, at night, behind the closed curtains on the window-sill, because it is likely to become intensely cold in so restricted an area. Ideally the aim of an indoor gardener is to maintain a continuous day temperature of 6o°-7o°F (i5°-2i°C) degrees with a minimum of 45°F (7°C) or a little higher at night. If a plant is caught by the frost, it should be put in a position remote from the fire and sprayed with cold water. It might then return to normal.

Humidity
It is realized by now that a good number of house plants have a preference for high or moderate humidity. This condition is coupled with the temperature and air circulation because in a closed area excessive heat dries the atmosphere to such an extent that it is harmful to many plants. This is therefore another thing to be watched. Control of humidity in a living-room is difficult. If it is overdone, some plants might revel in it, but human beings cannot stand it. Moist air is, however, more important to many house plants than warmth. So, if success is to be attained, it is necessary to provide humidity in the vicinity of the plants themselves. There are two principal ways in which this can be done. The first is to put the plant in its original pot in another rather larger one (which might well have a decorated exterior), and to pack the space on the bottom and sides with moist peat, which is kept continuously moist. (See Figure 6.) The second is to use a pebble tray. This consists of a tray or dish half filled with pebbles on which the pot is stood. Water is added to nearly cover the stones. This is topped up from time to time to compensate for evaporation loss. (See Figure 7.) Some plants, such as cyclamen, persicum and saintpaulia, respond well to a periodic steam bath. This is given by placing an upturned seed pan or block of wood at the bottom of a washing-up bowl and pouring into it boiling water to a level just below the top of the pan or block. The pot is stood on this platform for five minutes and then returned to its usual quarters. (See Figure 8.)

Syringing or spraying the foliage, particularly in hot weather, assists in maintaining a high level of humidity.

The Importance of Fresh Air
Fresh air, without draughts, is particularly beneficial to house plants. It clears the house of gas and other fumes.

Watering
Like all other plants, indoor plants must have water available at their roots in order to absorb nutriment from the soil and to enable them to manufacture their needs of starch (Photosynthesis). The problem that many owners of house plants have to face is when to water. It is very difficult to give a clear solution to this becauce so much depends on the nature of the plant, the season of year and the environment in which it lives. Plants with fleshy leaves, such as cacti and succulents, do not require as much watering as the plants with thinner leaves, because they are able to retain water within their tissues. On the other hand, plants with proportionately large leaves require more frequent watering, because they have a larger surface from which the plant breathes out water vapour. Again, there are generally two distinct periods in the year of the average plant, the season when it is growing fast and another when it is resting. During the first it needs plenty of watering, and this should normally tail off until the dormant period is reached, when the amount of water given should be quite small. Another important factor is the conditions under which a house plant is living. When the temperature is high and the light is bright, its demand for water is high. A plant kept continuously in a cool place requires much less frequent watering. Also a plant habitually needs more frequent watering if it is in a well-drained pot. If it is in a clay pot, from which the rate of evaporation is higher, it needs more watering than when it is planted in a plastic one. Plants in small pots and those that are becoming pot-bound also need more watering. On the other hand, newly re-potted ones and those in large pots should be treated more cautiously. It is difficult to lay down any hard and fast rules. Generally, however, it is better to under-water slightly rather than give excess, to allow the soil, which is darker in colour when it is moist, to dry out to a considerable extent before watering is repeated, and to give plenty of water during the spring and summer, i.e. the growing season, and little during the winter, i.e. the resting period. It is advantageous to use water with the chill off and perhaps, rather more difficult, according to some experts, to give rainwater or softened water, but in most cases it is not harmful to use tapwater.

Each watering must be thorough with a fairly long interval in between; a daily dribble is valueless. Because of the possibility of chilling when the temperature falls at night, house plants should be watered in the morning during the winter. In summer they should not be watered in direct sunshine as any water falling on them is likely to scorch the leaves.

Watering can be done in most cases, either by plunging the pots in water up to half their depths and allowing them to stay there until the soil is fairly moist, but on no account waterlogged. The water is absorbed by capillary action. After this, the pots should be drained and put back in their place. The other alternative is watering from above, in which case it is important to be sure that there is a space of at least one inch between the rim and the level of the soil, and to use a small watering can with a long, narrow spout, that can be inserted between the leaves so that they do not get wetted. It is important to remember, however, that some plants, such as cyclamen and saintpaulia, can be seriously damaged by having their leaves, stalks, and growing centres splashed. These must be watered from below. Unless they are aquatic plants, such as Cyperus diffusum or great moisture lovers such as Helxine soleirolii (Mind Your Own Business), house plants should never stand permanently in water in a saucer.

Methods such as packing wet peat around pots and standing them in pebble trays, have already been discussed on page 133 under 'Humidity'. These can help where the demand for water is very high, or if watering can only be carried out infrequently, or when the owner is away on holiday, of maintaining an adequate level of moisture. In addition, there are automatic self-watering and wick-watering pots on the market that are useful for emergencies, but none of these devices is a real substitute for personal attention. There are also inexpensive instruments available for indicating when water is necessary, but valuable as they are, their use must be tempered with experience.

Cleaning and Polishing Leaves
Plants grown indoors do not have their leaves washed regularly by the rain like their outdoor counterparts. Since the leaves play such an important role in maintaining health, it is necessary to see that their pores are kept free from dust and smoke grime, and that a film does not form on their surfaces which will reduce the amount of light reaching them. Although perhaps nowadays, with centrally-heated rooms and electric fires, this is not such a major problem, it is still necessary to keep the foliage clean and, of course, it improves the plant's appearance. Both the upper and lower surfaces of the leaves should be sponged with tepid water and if they are very dirty, soapy water can be used, but it must be thoroughly rinsed off afterwards. Plants with finely cut and delicate foliage must be cleansed by thorough spraying. Some people like to give the leaves a good shine, but olive oil, which does achieve this end quite effectively, tends to attract the dust, especially in the pores where it is easily lodged. There is, however, a proprietary aqueous wax emulsion that appears to be quite safe and that gives a shine lasting for months.

Feeding
There are no differences in the nutritional requirements of house plants from those of the multitude that grow in the open. When plants are first purchased they are usually fertilized for some months, but thereafter they benefit from small regular doses of a solution of a proprietary liquid manure (there are several especially blended for house plants), that can be given at the time of watering. Foliage and summer-flowering house plants should be fed during the summer and the winter-flowering ones in the winter. No plants should be fed during their resting time, otherwise they will be undesirably forced.

Re-potting
This is an operation to be postponed as long as possible because most house plants flourish best in what appears to be too small a pot. The day does come, however, when they are pot-bound. This is normally indicated by the slowing up of growth, rapid drying out of the soil and roots growing through the drainage hole. It can be confirmed by knocking out the root ball. If it consists mainly of a matted mass of visible roots and little soil, then the plant needs re-potting.

The pot chosen for this purpose should be the next size larger, perhaps two sizes larger in the case of a vigorous grower. If it is a clay one, a layer of crocks should cover the drain hole. This should be followed by a thin layer of peat, followed by another of potting compost. The plant is then removed from its old pot. The old crocks are taken away from the base of its root ball and a few of the matted outside roots loosened without disturbing the root ball. It is placed on top of the compost in the new pot and the space round it gradually filled, with gentle firming, with slightly moist compost until the level of the base of the stem is reached, which should be about an inch below the rim of the pot. After finally tapping the pot down several times, it is watered, placed in a shady place for a week and sprayed daily. After this, it can be put back in its usual quarters.

A good compost for this purpose is a mixture of two parts commercial potting compost and one part garden peat. In addition, there are nowadays several proprietary soilless composts that are recommended for this purpose.

In the case of very large house plants re-potting is difficult to do with safety. The difficulty can be overcome by top dressing, which consists of removing in the spring the top one to two inches of the soil from the pot, without disturbing the roots, and replacing it with a commercial potting compost with which has been mixed a little commercial base fertilizer.

House Plants during Holidays
House plants, like pets, must be considered at holiday time. Most people do not really want to bother their neighbours at such times. If the plants are thoroughly watered beforehand, they can be left in a cool place quite satisfactorily for the duration of a short holiday. If the holiday is rather more prolonged, the pots can be surrounded with moist peat, or stood on a water-filled pebble tray (see page 133). For such periods automatic watering equipment is useful. If the weather is warm, each plant after watering can be placed, pot first, into a polythene bag of suitable size and the top open edges closed by twisting together and binding them with transparent tape.

Indoor Plants in Trouble
Indoor plants, just as their outdoor counterparts, are likely to be infested with pests and be attacked by disease. The indoor gardener can nevertheless do quite a lot towards combating the effects of these menaces. If the plants are regularly inspected and the leaves kept clean, any pests can be picked off by hand, when there are only individuals present and before they get a chance to multiply; if any disease is detected in its early stage, timely action can prevent it spreading and becoming serious. Again, if indoor plants are given the environments and conditions that they like, they flourish and are able to meet adversity without difficulty. Unfortunately, even with the very best intentions, it is not always possible to prevent something disastrous happening. For this reason, some of the more common troubles are briefly discussed.

Pests
Aphides (Greenfly). There are few people not familiar with these troublesome insects, which are sap suckers. They cause the leaves and stems to become distorted and cover them with a sticky substance, called honeydew. The odd few can be picked off; if there are more, the plants should be sprayed with malathion or the systemic menazon.

Red Spider Mites. These minute red insects can be detected by the presence of a fine whitish silken web on the undersides of the leaves, where they live. The leaves acquire a metallic, greyish bronze look, become brittle and fall off. Plants kept in a fairly moist atmosphere are not usually attacked. Spray with petroleum white oil emulsion.

White Flies are sap suckers that cause the foliage to become mottled. In the case of serious attacks, the plants should be sprayed with malathion.

Scale Insects. In the presence of these insects, the stems and undersides of the leaves are covered with off-white scales, which are interspersed with areas of mobile orange scales-the young insects.
They are best removed with a thin stick, mounted with cotton wool soaked in methylated spirits.

Mealy Bugs, which look like tufts of cotton, feed on the sap, stunting their host's growth and distorting them. They are best treated as described under scale insects.

Diseases
The most common diseases are mildew and rot. Mildew. The leaves and stems become covered with a white powder and distorted. When mildew is detected, as far as possible the affected parts should be removed. The plant should be sprayed with Karathane. In the event of an attack, a check should be made to see that the plant is being treated in the correct way.

Rot is usually caused by over-watering and water being allowed to remain on leaves, stems and growing centres. Where feasible, the affected parts should be cut off. It can be prevented by not allowing water to remain on the plant. Sometimes a damaged plant can be resuscitated by keeping it fairly warm and only watering it very moderately.