Gardening Houseplants Laidback Gardener Tip of the Day Light Needs of Plants

How to Tell if your Houseplant Lacks Light?

This positively miserable aloe (Aloe vera) is trying to say, by its pale new growth: “Help me ! I’m dying from lack of light!”

The life of the indoor gardener would be much easier if plants could tell us when they were not happy with their lighting, because light is their only source of energy. It’s equivalent to food for humans, in spite of what fertilizer salespeople try to tell us (their claim that fertilizers are plant “food” is nonsense: plant get all their “food” from the sun.) But instead, plants keep mum… or rather, they try to tell us, but we don’t always understand the message.

Here are the classic symptoms of a houseplant that lacks light:

Illustration drawn from the book Houseplants for Dummies by Larry Hodgson.

Weak, elongated, pale green growth: In horticultural terms, this is called etoliation, the most easily recognized symptom of lack of light.

Abnormally small leaves: When they lack light, some plants produce new leaves that are smaller than existing ones.

Leaning toward the light: All plants bend towards their light source over time, but if the leaning is exaggerated, the plant probably isn’t getting enough light.

Lack of bloom or poor flowering: Plants need more light to bloom than they do to simply grow. A mature, healthy flowering plant that fails to bloom at the appropriate season or blooms only weakly or sporadically probably isn’t getting enough light.

Cactus are very slow to react to low light. To produce the etiolated growth seen above, this cactus probably sat for at least a year in inadequate light.

No growth or abnormally slow growth: Many foliage plants and succulents react to insufficient light by growingly slowly or by ceasing to grow altogether. They simply live on their stored energy, sometimes for months, until they use it all up, and then they begin to show other symptoms of insufficient light.

Leaf loss: Plants typically shed older leaves, but if you notice laves falling off abundantly, you can suspect lack of light. While many outdoor plants lose their leaves in the autumn, this is not normal for most houseplants (other than a few flowering bulbs).

Root root or stem rot: Plants that receive too little light can’t absorb water properly and their potting mix remains excessively moist, leading to rot.

What to Do

As soon as you notice one or more of the symptoms above, move your plant to a spot with better light: a south-facing window, under artificial lighting, etc. The  plant should soon begin to grow normally again.

Worse in Winter

Note that plants are much more likely to lack light during the short days of winter than during the summer. And as soon as days begin to lengthen, starting in late February or early March in the northern hemisphere, the problem will often correct itself and you can move your plant back to its original home… if it’s still alive, that is.

However, it’s never a bad thing to give plants as much light as possible during the winter months, again by placing them in front of the brightest window possible or under artificial lighting.Pelarg+

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

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