Light is essential for plant life since it provides the energy needed for growth. The light requirements of different plants, however, vary widely. Some types will only flourish in bright sunlight whilst others tolerate shadier conditions. The levels of light indoors also show dramatic differences, not only in the different areas of the house but also within individual rooms. So one of the secrets of successful indoor growing is to position the plants where the light level is most suited to their particular needs.
Day Length is another factor which influences plant growth. Plant food production reaches its peak during the long days of summer and declines as the nights lengthen with the approach of winter. Consequently, most foliage plants pass into a resting phase during winter regardless of the amount of sunshine. At the same time their requirements for water and plant foods are also at a low ebb. So liquid feeding is not needed and watering should be kept to a minimum.
The best lit place in a house
The best lit place in a house is close to a window which faces south and so receives direct sunlight for most of the day. This suits pelargoniums, many other flowering plants and cacti, but there is a risk of leaf scorch with indoor foliage plants. Even in the case of flowering plants it is preferable to have net curtains to diffuse the light.
Plants on window sills
Plants on window sills are, however, subject to a big overnight fall in temperature, particularly when the curtains are drawn. Consequently it is advisable to move them into the room during the night in cold weather. Plants growing on window sills tend to bend towards the light and their growth becomes lop-sided. The easy way to prevent this is to turn the pots a lithe every few days, so that the plant is encouraged to remain upright, but don’t do this to flowering plants which are budding as it may cause the flower buds to drop off.
Away from the window
Moving back a little way from a south-facing window the light is still bright, but plants standing in this position are only exposed to direct sunlight for part of the thy. So too are plants on the sills of windows facing east orwest. These conditions suit most flowering plants and are also suitable for some foliage types.
A limited range of indoor plants can even be grown in shady parts of the house, provided that the level of light is such that reading is possible. Plants which normally require higher light intensities can also be grown here temporarily for a month or two. They will, however, need to be moved into better lit areas to recuperate.
Effect of colour
Indoor lighting levels are markedly affected by the colour of the walls and ceiling. Light colours reflect the light and increase the general level of illumination in a room. Dark shades on the other hand absorb the light and so lower the light intensity.
Many other factors such as the size of the windows and the presence or absence of nearby large trees or buildings affect the levels of natural lighting in a room. So it is impossible to lay down exact rules as to what types of plants can be grown successfully. What you need to do is experiment with placing the plants in different positions and then keeping a dose watch on their appearance. When the light intensity is too low there will be little growth and what does develop is likely to be drawn out and spindly. Young leaves tend to be smaller and paler than those grown in adequate light whilst old leaves are likely to turn yellow and fall prematurely.
Low lighting levels
Low lighting levels have a particularly severe effect on flowering plants. Flower bud production is greatly reduced and any buds which do develop generally give poor quality blooms.
Most houseplants do best in bright but diffused light.
Prolonged exposure to direct sunlight on the other hand can cause leaf scorch on many foliar plants and some flowering species. The degree of damage varies widely. Whole leaves of particularly sensitive varieties may shrivel and turn brown whereas in more resistant types the damage is usually restricted to the leaf tips and edges.