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Houseplant: Light and sunlight

Light requirements vary depending on the plant. For healthy indoor plants, light should respect the plant's native environment as much as possible.

Plants light and growth

One of the biggest challenges in growing houseplants is getting the lighting just right. But light can vary in both intensity and quality.

Plant growth is dictated by plant hormones, called auxins.The pigments in the leaves capture the light to give the leaf its colour. They circulate through the plant and are responsible for the length and width of the cells in the stems, leaves and flowers.

Outdoor plants can capture light rays from all directions, which enables the auxins to circulate in a uniform manner through the plant. Growth is then even all over the plant.

But the story is different for houseplants. They often get light from only one side. This affects the circulation of the auxins and the result is a lop-sided plant.

TIPS:For healthy plants, keep turning your houseplants a quarter of a turn every time you water them. That way light will reach all sides of the plant.

Light intensity - too much or not enough!

Light intensity is the amount of light that actually gets to the plant and the ideal will vary from plant to plant. If a given plant gets too much or too little light then the process of photosynthesis will be disrupted and growth will be stunted.

Too much light destroys the chlorophyll

  • The leaves will tend to yellow
  • Patches will develop
  • The leaves will turn brown and dry out

Too little light

  • The plant go leggy (distance between the buds gets too long)
  • The stems weaken
  • The leaves turn yellow and new ones are smaller
  • Two-tone leaves turn green
  • Flowering plants stop blooming

Begonias are plants that adapt well to low light intensity.

Understanding light

Light is generated by the movement of energetic particles called photons. Each colour in the light spectrum has its own wavelength and with the human eye we can basically see seven: red, orange, yellow, green, blue, indigo and violet. These are the rays situated between 400 and 750 nm. Plants use mostly the rays between 445 and 750 nm: violet/blue and orange/red.

  • Blue rays : important for compact and leafy plants
  • Red rays : encourage growth and blooming

Choosing the right type of light

To make a long story short, your plants need either a good source of sunlight or light from specialized grow-lights.

  • Sunlight is perfectly adapted to the needs of plants, unlike the classic incandescent light bulb.
  • The light emitted form a light bulb is too intense (650-700 nm) to be effective for use by plants. Your average incandescent light bulb just doesn't make the grade.
  • Traditional fluorescent tubes do better but do not offer as complete a spectrum as grow-lights.
  • Grow-lights are more expensive but they are recommended for growing plants indoors.

Sunlight for Every Season

A south-facing window is where you will get the most light and heat into your house.

  • From November to March the sun's rays are less strong and so a southerly window is required for many plants to compensate for the drop in light in the winter.
  • During the warmer months, if a plant that doesn't require great amounts of light is put in a southerly window, its leaves are apt to burn.

East-facing windows provide sun in the morning and then the rest of the day they are cooler. There is enough bright sun but it isn't too intense.

This is ideal for your ferns and gesneriaceae (African violet, Elephant's ear, Florists' Gloxinia, Aeschinanthus)

West-facing windows are the place to put your plants that require only a few hours of sun a day.

Your north-facing windows are probably too dark in the winter and may be good only for certain plants during the summer months.