Growing house plants does more than bring beauty and interest indoors. It keeps us in daily contact with nature, which is something everyone needs.

In everyday living, particularly in the cities, we tend to forget our dependence on plants. They recycle and purify the air we breathe, absorbing carbon dioxide we exhale and replacing it with oxygen vital for our existence. And they supply our food, either directly or indirectly, and much of our materials. Survival without plants would be impossible.

It goes deeper than a matter of dependence. We form some degree of emotional affinity with plants. This involvement is understandable of a more special kind with house plants because when brought from their forest or desert they are completely dependent on us for water, food, and a livable environment.

We can unwind a little by taking the time to watch the miracle of new growth and other changes in our plants.

This guide deals mainly with foliage plants and the general care needed to keep them growing attractively for years. Flowering plants – with a few exceptions, like cacti and possibly tuberous begonias and gloxinias – are better renewed each year for indoors.

THE CHOICE

First, think of the situation you can offer. Providing that the room is reasonably airy but free of draughts, light is the most important consideration.

These plants are happy in rooms with only average light (but also in brighter indirect light): Aspidistra, aglaonema (Chinese evergreen), asparagus fern, bromeliads, Cissus Antarctica (kangaroo vine), Dumb canes, Dizygotheca (finger aralia), Dracaena, fatsia, Fatshedera, ferns (fishbone and Pteris), ficus (rubber tree), Fittonia, maranta (prayer plant), monstera, palms (if not too dull), ponytail, poinsettia, Rheo (Moses in the cradle), sansevieria (snake plant or mother-in-law’s tongue), tradescantia.

Remember that colored or variegated types will look less colorful in a poor light.

These must have indirect but bright light: African violet, aluminum plant, anthuriums. aphelandra. artillery plant, aucuba, avocado, Brassaia (umbrella tree), begonias, bananas, cacti, coleus, crotons, cyclamens, ferns (maidenhair and bird’s nest), gloxinia, hoya, jade, peperomias, pick-a-back, spathiphyllum, succulents, weeping fig, zygocactus.

Sunshine and an outdoor airy position are needed for geraniums or pelargoniums and potted roses.

Be your own specialist. Most house plants remain happy under a variety of conditions and treatments, but their appearance will let you know if all is not well. Once you get to know your plants any changes will become obvious.

An adverse symptom need not be linked with pest and disease problems. It can be due to an unsuitable aspect, incorrect watering or feeding, or lack of humidity. In a new plant, it may be a temporary out-of-sorts period while it is adjusting to a new environment.

WATERING AND FEEDING

Everyone wants to do the best for their plants but when it comes to watering some people are forgetful or, with good intentions, restrict watering too much, while a still greater percentage over-water.

It is impossible to lay down just how often water will be needed as this varies according to the type of plant, its size in relation to the pot, and the temperature, light, and atmosphere of the room. Some ferns may need water every day during summer, while most other foliage plants will want it only once or at the most twice a week.

So it is a good idea to make a twice-a-week schedule, not necessarily to water but at least to check the water requirements of your plants. With set times when you are most likely to be home, such as Sunday mornings and Wednesday nights, there is less chance of forgetting this important duty to your plants. Daily drinkers, such as ferns in shallow containers, can be placed where it is convenient to pass them a quick shot of water each day.

Remember that over-watering is almost as harmful as leaving the plants too dry. Plant roots need small quantities of oxygen entering the soil, and over-frequent watering prevents this; also the soil can become sour and unhealthy.

Therefore aim to let the soil almost dry out between waterings so that roots can breathe and the soil benefit from a good airing. A sound general rule that helps to achieve this easily is to leave enough space between waterings to allow the surface soil to dry out.

After a while, just a glance at the soil may tell whether water is needed.

However, different soil mixtures do vary in color and texture. So until you are accustomed to soil appearance make it a rule to water most house plants only when the surface feels dry but there is still some slight dampness a centimeter or two below the surface.

Some plants such as snake plants (sansevieria), cacti, jade, and other succulents can be left to get a little drier still, especially during the cooler months.

On the other hand, some others, like the ferns, are happy with a continuously damp surface during the warm months or where growing in centrally heated buildings, especially when in a well-lighted aspect. These include aluminum plant (Pilea Cadierei), artillery plant (Pilea microphylla), coleus, Chinese evergreen (aglaonema), ficus or figs, Fittonia, pothos, maranta, monstera, Moses in the cradle (Rheo), peperomias. philodendrons, Peace lily, Syngonium, pick-a-back (Piggyback plant), tradescantia, and Elephant’s ears.

Others, such as aralia, aucuba, Fatshedera, asparagus, and ivies, are adaptable.

Begonias – the rex, tuberous and fibrous kinds – also like a fairly damp surface when well ventilated and the atmosphere is normally dry, but in periods of high humidity do the watering only when the surface dries out, otherwise leaf or stem rots may occur.

Crotons appreciate a damp surface during summer if grown in bright light, but need to be allowed to dry out a little in winter.

These points are given as a general guide only. The plant requirements vary in different environments. You can make your own allowance for these, using as a key the knowledge that a plant’s three vital requirements – moisture, temperature, and light – must be kept in the ratio: when light is considerably reduced, then temperature and water should be correspondingly reduced; and conversely, plants in warm, bright aspects can take more water than those in a cool, dull position.

How much water?

Except in a few cases mentioned later, water should not be rationed. When it is time to water give all that the soil can take. Give enough to run through the drainage holes into the saucer below the pot (make sure this surplus is tipped out, as plants should not be left standing in water).

In practice, you will after a time know how much water is needed to bring a pot of soil from the nearly dry to the fairly damp state. One pot may need only about half a cup but another could want two or three times this amount.

However, there are pitfalls. When the soil has been allowed to get too dry the water you give it may only wet the surface then trickle down the minute crack between pot and soil, running out of the drainage holes without penetrating dry soil directly below the plant.

So if a pot is very dry it is just as well to water by soaking it to at least half its depth; or give enough to nearly fill the pot saucer and do not empty the saucer for about an hour (you may find after this time that the run-off in the saucer has actually soaked back into the soil).

Some of the exceptions where you may ration water are with cacti and other succulents in unheated rooms during winter, or with African violets. The latter never like to be overwet and, when watered liberally, the peaty soil they are usually grown in seems to stay saturated for too long. I like to leave them until the surface soil feels dry, then give about half a cup of water, tilting the bowl to spread it evenly over the surface.

When growing plants in bowls or fancy pols without drainage holes, prop the container on its side for 20 minutes or so afterward so that surplus water will drain away.

Water temperature

Very cold tap water can shock plants. To be on the safe side you might add just enough hot water to the watering container to take off the chill without making it noticeably warm.

The exceptions that would resent warmed water are cyclamens and bulbs such as tulips, hyacinths, and lily, especially in early growth before flowering.

In districts with hard water, it is a good idea to flush out residues that gather in the soil every few months by standing the container in a bucket of water, then giving several more waterings to encourage plenty of run-off from the drainage holes. If you can spare rainwater for the flushing then so much the better. Do not use water from water softeners.

A white crust can form over the soil from hard water, or sometimes from fertilizers and even from the decomposition of organic matter. This should be scraped off.

Feeding

Many of the house plants bought these days are fed on plant pills or other slow-release preparations which keep on feeding for months. It is unfortunate that plant labels do not yet give some indication of when the plant will need feeding again. Even if you see on the soil the telltale buff-green beads of Osmocote, a slow-release fertilizer now popular in nurseries, it is difficult to tell whether this was used six weeks or six months ago.

So it is unlikely that a new plant from a nursery will need feeding for at least six weeks, and even then for the next month or two, it is advisable to keep down to half the strength recommended.

In any case, the need to feed foliage plants is usually over-emphasized. Nurseries feed these plants so that they reach a saleable size quickly, but quite often their new owners are not anxious to see any appreciable increase in size. After all, who wants an umbrella tree or rubber plant pushing against the ceiling, or a philodendron that needs training more than twice around the room!

So their feeding should be only minimal to keep the plant healthy, which would amount to about a quarter of the normally recommended rate every six to eight weeks.

Flowering plants such as cyclamens. African violets, gloxinias, and begonias need more feeding for good performance, but even here it is safest to use only about half the amount of soluble plant food or plant pills generally recommended. In this case, the soluble foods could be used every three weeks up to the time flowering is normally finishing.

Remember that more potted plants are killed through over-feeding than by starvation. The problem is greatest with plants that are normally allowed to nearly dry out between waterings because as moisture in the soil decreases so the concentration of fertilizer salts in the container increases.

Apply plant foods soon after watering when the soil is evenly moist, and take a little extra care to see that it does not become too dry for at least a fortnight afterward. Feed only during the active growth period which, with a few exceptions, such as cyclamens, will be from spring until early autumn.

LIGHT

This is almost as important as water. Plants need light as energy to make sugars and starches essential to their make-up.

Without enough light, most plants become thin, weak, and drawn. However, there are others that are relatively at home in poor light, mainly because they come from jungles where they grow beneath a dense leafy canopy of trees and vines.

These include aspidistras, most bromeliads such as Billbergia, Aechmea, Neoregelias (except coloured leaf types), aglaonema or Chinese evergreen, ficus, palms, chlorophytum or spider plant, and ivies.

However, these also adapt to good light demanded by the majority of house plants. “Good light” can be an ambiguous definition, but regard it as an area where the indirect light in a room is bright enough to throw a faint shadow when a finger is held about 10cm (4in) above paper or a similar light surface. Good light can also be described as an area where normal electric lighting switched on during the day will not appreciably brighten the position.

Don’t despair if your house lacks well lit areas. In America and Europe there is now a popular trend to have plant rooms where small jungles of exotic plants flourish. These are often made in converted windowless cellars or other dark areas by installing artificial lights.

Special daylight-type plant lights are often used, but a pair of 40 watt fluorescent tubes with a reflector behind them will give enough light for a well filled planter box directly below them. Plants are placed from 10 to 30cm below the tubes, which are left on for 10 hours to simulate a bright day. They are normally controlled by clocks.

Even a table lamp with an ordinary incandescent globe will help to supplement the light needs of a plant in a dull corner, though not as effectively as fluorescent tubes. Spotlights can be used to emphasise and feature special plants and if used regularly can help to compensate for lack of natural light.

TEMPERATURE AND HUMIDITY

These may be regarded as separate factors but in the plant world one is dependent on the other.

Generally speaking, plants can tolerate about the same temperature range as we can but, except for succulents, can only cope with the higher temperature end of the range when humidity increases in proportion to the temperature. They would not need steambath humidity but only about a 50 percent relative humidity, which is a normal comfortable living condition.

This is automatically maintained in many districts by nature: as temperatures rise there is a greater rate of evaporation from moist soil, lakes or the sea. However, the natural atmosphere of comparatively dry inland areas may be too dry for many plants.

Indoors, the normally high relative humidity can come crashing down to unsuitable levels when radiators are used to heat already fairly dry air (cold air holds very little moisture).

A similarly dry atmosphere develops when the air in a room is heated by sun on closed windows. It makes an environment still less favourable for plants if blinds or heavy curtains are drawn, as this also upsets the water-light-temperature ratio.

In other words, plants have a better chance of standing high temperatures if the light intensity is high, and in this circumstance they will also appreciate much more water than other plants in a cool room with little light. For the same reason we let plants have a drier soil during winter in unheated rooms.

Create humidity – A humid microclimate can be created around the plants by providing a moist surface area, which supplies moisture to the atmosphere by evaporation. The rate of evaporation automatically increases as temperatures rise, and as long as there are no draughts the moist atmosphere lingers around the plants.

There are a number of ways you can supply this moisture. One is to have a few centimetres of water in shallow trays holding a sufficient depth of pebbles to support the pots just clear of the water.

Or place moist sphagnum moss, peatmoss or even water-holding sponges in planter boxes between the pots. Just grouping a number of pots together helps to create humidity from the moisture that evaporates from their soil.

Low temperatures – Temperatures below 10 to 15°C (50-60 Fahr) are not appreciated by most of the foliage plants but can generally be tolerated providing that light and especially water are also reduced. However, avoid drastic changes such as would occur where the room temperature may rise to 27-30°C (80-85 Fahr) while radiators or other temporary heaters are used during the first half of the night, then drop to about 10 degrees during the hours before dawn.

Plants behind closed windows can also experience similar variations between night temperature and the maximum on a sunny winter’s day. These fluctuations will be greatest close to the glass. Although there are a few flowers such as cyclamens, chrysanthemums and geraniums that will accept such a great temperature fluctuation, most foliage plants would be happier kept about a metre from the glass, or even further to avoid direct sunlight.

PESTS AND DISEASES

Mealy bugs are probably the most serious pests to house plants, attacking particularly ferns, tolmiea or pick-a-back plant. African violets and cacti. They are about the size of a flattened match-head and, like an aphis, covered in greyish-white down; found mainly along the veins on underside of leaves, along steins or in leaf joints, either singly or in downy clusters. A sugary substance that later turns black may also be present.

One way to rid a plant of mealy bugs is to touch each one with a cottonwool swab moistened with methylated spirits. Sponging with soapy water is also effective. Where mealy bugs are likely also to be at the base of the plant in loose compost, water the soil liberally with malathion made up to spraying strength – but because of the smell choose a time when the plant can be left in an outdoor sheltered spot for a day or two afterward.

Aphis may attack young leaves of philodendrons and other foliage plants, also young fronds of ferns and sometimes gloxinias or African violets. Sponging with soapy water will remove them from all but downy-foliaged plants.

The general range of pyrethrum-based household pressure pack insecticides are also effective. Choose a water-based type, or else, if in doubt, place the plant in a cardboard carton and spray insecticide to mist the inside area but without spraying directly on the plant; then cover for a few minutes to seal in the vapour.

Red spider mites – These almost microscopic mites below foliage cause a dull sandy-looking mottling. They sometimes attack gloxinias, fuchsias or pick-a-back plant, particularly when the atmosphere is dry and warm.

Sponging with soapy water controls them on smooth-foliaged plants. Alternatively, and for gloxinias and other downy-foliaged plants, place in a carton as suggested under aphis and spray with dichlorvos household insecticide.

Thrips sometimes cause a silver-grey mottling on leaves of fuchsias, Cissus rhombifolia (rhiocissus), rhododendrons and lauristinus. Slender needlepoint-size pale green to black insects may be seen, usually below foliage.

Sponge as suggested for red spider mite or spray with water-based household insecticides.

Scale – There are many types of scale pests. The only thing they all have in common is that they can be removed by gently scraping with the fingernail, so check if not sure.

Oil sprays and systemic insecticides are used to treat scale on garden plants but indoors, or on balcony container plants, it is usually preferable to rub them off with a soapy cloth or, if on rough stems, with an old toothbrush and soapy water.

Base or collar rot – This can attack geraniums during humid conditions when the soil is wet. and sansevierias (snake plant) if the soil is not kept fairly dry during cool conditions.

Restart the geraniums from cuttings taken from the top of the plant where growth is still healthy. Tap sansevieria from its container, dust bordeaux or copper spray powder over the exposed crown and keep it dry until warmer spring weather, then repot and water just enough to evenly dampen the soil.

Bacterial blight of ivy is a disease apparently rare in Australia until the early 1970s. Sections of leaf brown and dry, surrounded by a yellowish hole. Pick off and burn badly infected leaves, then spray the plant with bordeau or copper oxychloride.

Powdery mildew – This is a greyish powder over leaves and sometimes on flowers of African violets. Remove old flowers and spray with Benlate in an outdoor shaded position.

Leaf spot – Rex and tuberous begonias develop transparent to brown spots during very humid conditions, especially when not well ventilated or when the soil is over-moist. Spotting may spread to destroy the leafand even the stem.

Remove badly damaged leaves and spray with Benlate in an outdoor sheltered position. Sun on water droplets may sometimes cause spotting. Also see Scale.

LEAF CARE

Dust gathers on the leaves of house plants just as it does on furniture. It not only dulls the plants’ appearance but slightly reduces light penetration of the foliage. There are cases where it blocks breathing pores, but these are mostly on the underside of leaves.

In any case, plants look happier if leaves are dusted or sponged at least every second week. There are several good leaf gloss preparations on the market which give foliage greater lustre and also have an anti-static effect that stops dust from adhering. White oil is also sometimes used as a leaf gloss but is inclined to collect dust. Do not use foliage sprays on any but smooth leathery leaves.

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