General Cultivation

Temperature and humidity

Many house plants will stand a considerable variation in temperature though they do need protection from frost, and, of course, it is best to avoid a high temperature by day and a very low one at night. But the air humidity must be adequate whatever the temperature; dry air is very bad for plants and causes discoloration, withering and dropping of the leaves. Now the amount of moisture which air can hold increases as the temperature rises; therefore, given only a limited amount of available moisture, air in a cool room is likely to be relatively more humid than that in a hot room. If plants are to be grown in fairly warm conditions, especially if centrally heated, they must either be chosen for their dry-air resistance, or the local humidity must be improved. This can be done in several ways. Occasional misting of the foliage with clean water from a fine-nozzled syringe or spray bottle does a lot of good. The simplest means, however, is to stand the pots on a tray of pebbles or grit which is kept damp below pot level, or to use a trough-shaped container and plunge the pots in moist peat or sphagnum moss. Single pots can be stood on a block of wood surrounded by water in a saucer; it is often an advantage to use boiling water as the rising steam damps the leaves admirably. The water must not come up to the level of the bottom of the pot. With any of these methods water will evaporate steadily and provide air humidity around the leaves.

Ventilation

Stuffiness should be avoided, and fresh air supplied when the weather is not cold. But nothing kills a plant quicker than a draught.

Natural light

Most house plants prefer good indirect light, though sunlight rarely harms them. Spindly growth indicates lack of light. Plants tend to turn their stems and leave’s towards light; turn them regularly to avoid uneven growth.

Artificial light

Electric light can be used to good effect in dark positions, to assist the flowering of difficult plants like African Violets, or to keep plants in indoor greenhouses growing properly. Fluorescent mercury-vapour tubes are recommended, particularly those suggested for plant cultivation which have a ‘warm’ light. Such tubes, which should be 9-12 in. apart, can be as little as 9 in. above African Violets, but for ordinary plants 18-24 in. is adequate. If the tubes are the sole or main source of light, they should be kept on for 12 to 16 hours a day.

It is possible to buy made-up units con-sisting of a tray for plant pots and a simple frame which supports a 2 ft. fluorescent tube above the plants.

Ordinary incandescent bulbs give out less light and much more heat per watt than fluorescent tubes. For this reason they will scorch plants if too close, and are seldom of value to help indoor plants.

Watering

The aim when watering should be to prevent the soil from ever drying right out while avoiding sodden conditions which can be quite as bad, especially in winter, resulting in stagnant, airless soil in which the roots rot. When the soil starts to become dry – be guided by the look and feel of it; dry soil is hard to the touch and greyish-white in appearance — give a thorough watering. Never water in continual driblets, nor let plants stand in water-filled saucers. In summer, plants may need water two or three times a week, and an occasional soaking of the whole plant is beneficial; in winter, weekly or even fortnightly may be enough, depending on room temperature. A watering-can with a long, narrow spout will be found to be the most useful, since the water can be directed accurately into small pots and among foliage. It is advisable to use water at room temperature: some plants will drop their leaves or rot if chilled.

Watering presents difficulties when one goes on holiday. If no one can be found to do this, a useful tip is to soak the pot thoroughly and then put it in a polythene bag, either tying this round the stem of the plant at soil level or enclosing the whole plant within it. A pot so wrapped should keep damp for two or three weeks. An alternative is to use thin wicks or domestic tape leading into the pots from a vessel of water placed above them. The wicks should be soaked first to encourage the flow of water to the pots by capillarity. Put the plants in the coolest and shadiest place available – a larder is excellent. Many plants will tolerate standing in water in a sink for not more than two weeks, but let them drain thoroughly after this treatment.

Cleaning

Inevitably plants in a room become dusty, and in a town industrial grime may also accumulate on them. Apart from looking unpleasant and reducing the light reaching the leaves, this will clog the breathing pores of the leaves. Plants may be syringed or dipped in tepid soapy water, and then rinsed in clear water; a good place to do this is the bath. Those which cannot be moved should have their leaves gently sponged. Washing in this manner will also help to keep down insect pests. It is, however, important to ensure that water does not remain on leaves, especially hairy ones, or in the angle between leaf and stem, as rotting or scorching may follow.

Acclimatisation

It is best to buy plants in late spring and summer when conditions in the grower’s greenhouse and your room are fairly similar. In winter the difference between these sets of conditions can be enormous and the plant receives a considerable check in its move. A summer-bought plant will also have the opportunity to acclimatise gradually to quite poor winter room conditions.

Re-potting and feeding

After a season or two, pots become filled with roots (pot-bound). At this stage a shift into a slightly larger pot is desirable, and is best done in early summer. A good compost recipe is 2 parts of fibrous loam, 2 parts of rotted leaf-mould or peat and 1 part of coarse sand. Alternatively, John Innes Potting Compost No. 1 can be used, adding 1 or 2 parts of leaf-mould or peat to every 3 parts of compost. The soil-less composts based largely on peat, now freely available, are quite satisfactory for house plants but the nutrients in them are soon used up so that plants must be fed regularly after two or three months. This also applies to plants grown in the first mentioned compost recipe.

Newly bought or re-potted plants in soil-based composts will not need feeding, but those beginning to become pot-bound may be fed during the summer. Use a balanced fertiliser, preferably in weak solution, according to the maker’s instructions once or twice a month. Overfeeding results in weak growth and scorched foliage.

Both plastic and clay pots are equally suitable for house plants but remember that plants in plastic pots will need watering less often, while the clay pots must be well crocked to assist drainage. Topdressing Plants which dislike being re-potted may have the soil partly replenished by topdressing. This consists of removing the top 1 or 2 in. of soil from the pot, taking care not to damage any roots, and replacing it with fresh compost containing fertilisers.

Cutting back

If plants grow too leggy, or if bushy growth is desired, many will benefit from being cut back periodically or from having the growing tip pinched out. Some rather difficult plants, like aphelandras and pileas, may lose most of their leaves during the winter. If so, cut them back to 2 inches above soil level in spring; new growth should sprout from the base.

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