Light for houseplants
By Jille Kuipers
Light is essential for plants. It enables them to produce their own food and energy through the photosynthesis process. It also helps them with hormone production to develop plant organs and induce flowering. The right light will support the plant’s ability to grow well and stay healthy.
If lighting conditions are suboptimal, plants will be more stressed and experience problems such as weak growth, minimal flowering and more prone to disease. A plant can often survive low light levels for a while, but it won’t be able to thrive, grow bigger, or flower. Signs of insufficient lighting are plants that start to stretch, grow thin, lose color or variegation, and have smaller leaves. Too much light can be recognised with burn marks on foliage, and wilted and shriveled leaves. The right light will help you to grow thriving plants, with healthy color, compact growth and normal size leaves.
What is the ideal light level?
The ideal light level depends on the plant species and its prior growth environment. Check the plant label to see what level of light your plants prefer.
Often labels will show: low, medium or bright light.
Away from bright windows, plants get some light but not direct sunlight. Most of these plants are foliage plants (i.e. plants without flowers but with relatively sturdy leaves) e.g. Cast-iron plant, Chinese evergreen, Dieffenbachia, Dracaena, Lady palm, Parlor dalm, Peace lily, Snake plant. If you’re based in the northern hemisphere (Europe, UK, North America) your window could be north-facing, where plants get light but not full sun. These windows have the relatively weakest light intensity. Shade-loving plants can grow here, especially during the summer months. During winter, it is likely that the light intensity and duration are not supportive enough. This type of daylight has a relatively higher blue content with less deep red and far red. Combined with a relatively lower light intensity it won't be enough to promote flowering. If you’re based in the southern hemisphere (Australia) your window could be south-facing, this is because the north-facing window will receive a lot of sunlight, as the sun shines from the north.
East or west windows, where plants will receive light early morning or in the late afternoon. Example plants are: African violet, Begonia, English ivy, Ferns, Fig, Nerve plant, Peperomia, Schefflera, Spider plant. In the northern hemisphere, the east-facing windows receive morning sun, although not very strong. West-facing widows receive afternoon and evening sun, which makes this a place for plants that love medium to high light. Morning and evening light contains deep red and far red which can help plants to get into flowering mode together with the right day/night length.
Herbs and succulents love the full strength of daylight from a south window (if you’re in the northern hemisphere). other plants are Cactus, Jade plant, Citrus, Orchids, Croton. Peperomia Purple, Flowering maple, Hibiscus and Passion plant. Note that plants in high-light environments might require more watering as they drink more and photosynthesize at a higher rate.
Rules of thumb
Aside from these directions you can use these rules of thumb: The closer to the window, the brighter the light. The sharper the shadow, the brighter the light. A fuzzy shadow is medium light. No shadow means low light.
If you’re only having bright light windows and you feel your plants require less light, you can move them away from the window. e.g. if you’re having plants that do well in a west-facing window, you can also place them a few feet away from a south-facing window. You can also use curtains or diffused paper to avoid direct sunlight on your plants.
The intensity, duration and direction of natural light vary between seasons. e.g. in the summer seasons the sun is high in the sky and the lighting hours per day (duration) are generally longer. However, the rays are very direct and an overhanging roof can block the light from coming into the house.
Other factors that influence light intensity are trees, the surrounding built environment and double or triple-glazed windows can reduce light. Reflective surfaces or white-colored paint can enhance it. Rotate and relocate your plants to make sure all sides are getting enough light.
Note that most plants for sale have grown a greenhouse. In general, that means a very optimal environment for plants including a very good light intensity. Note that it would take some time to adjust these plants to your light conditions at home. Another example is when you move plants from outdoor to indoor. This can cause leaf drop and yellowing. This is because outdoor lighting conditions can easily exceed 300 to 500 micromole/m2/s which is the metric in which plant-centric light is measured. In a greenhouse it can be easily 60 to 500 micromoles. At home these lighting levels are very rare and likely to be from 5 to 100 micromole.
During the winter season, the day length can be relatively short and grey and it could result in stretched plants, thin plant growth or easily damaged leaves. During these periods you can use grow lights to provide adequate lighting levels and help plants to grow well. Grow lights are also a good solution for a relatively dark spot in your house. If your are looking for easy to use lights with your existing desk-lamp or floor standing lamp you can use the Bloomer 2. If you are growing seedlings, leafy greens, edible flowers or in a grow shelf or cabinet you can use the home grow light sets.