Consider the interrelationship of light, water, humidity and temperature when growing indoors.
A friend of this column called in to a relate a sad houseplant tale, one that points out the importance of knowing all aspects of houseplant care.
In winter, most plants are dormant and should be treated accordingly. That means equal attention to each aspect of your indoor plants, including so little water as to keep them dormant, and how those aspects affect one another. How many of us have put a favorite plant (in my case, it was an old, reliable rosemary) in a south-facing window for the cold season only to see it wither because of temperature fluctuations and lack of humidity?
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Light, little water, proper humidity and temperature (PDF); take away any one and your houseplant suffers. As I did with my rosemary, we sometimes over compensate on one of the plant’s needs while ignoring others. Certain tools can help us keep an eye on things, things like humidity that we might otherwise ignore. The ability to monitor and pay close attention is an important gardening skill.
Which brings us to our friend. He bought a small potted succulent for his love at the Santa Fe, New Mexico Farmers Market, a keepsake of their high country life. It survived the long journey to their new home, an island in the Salish Sea of Washington state and was doing well in a south facing window over the kitchen sink, thriving in all that humidity from dish washing without being watered.
But then someone noticed that its well-drained gravelly soil was dry. That person, we won’t say who, watered it thoroughly as they’d been taught to do in summer, then let it drain in a saucer that immediately filled with water. It sat like this for no more than a day or so but the damage was done. First the speared leaves started dying off from the outside in, a sign of progressing root rot. When it looked like it was in its final throes, spider mites jumped in to finish off the carcass.
Our friend, always a champion of knowledgeable plant care, said that the killer, er, the person who over watered, knew one principle of plant care but not when it applied. She didn’t know that winter is a season of letting plants completely dry to protect their roots. She didn’t know that succulents were a special case. She did what she knew. She didn’t know what she didn’t know so she didn’t do it. Or didn’t not do it.
We’ve written before about winter houseplant care. But we didn’t stress how important it was to consider how changing one aspect — humidity, light, temperature — could affect the others.
Reducing water during the slow, dormant, winter months is critical to almost all house plants (except indoor citrus, say a potted orange or lemon tree; they need to be kept moist). But plants still need humidity. And they need it consistently.
Winter can be brutal on the humidity a plant needs for its health. Forced air furnaces and other heating methods can wring all the moisture from inside your house, a fact evidenced by our own dry skin. The usual remedies — nearby water-filled stone-filled saucers, misters — don’t help all that much. Having a plant near the kitchen sink can help. And everybody knows somebody who brings their potted ferns into the bathroom when they shower.
For consistent humidity, we pretty much need a humidifier. Now our friend in the fog-shrouded Pacific coast may not need it — though he claims he does when the furnace is running a lot, which is seldom — but most of us in the plains and mountain-west, the southwest, midwest, and even places in the summer-muggy south would be doing our plants a favor if we used one during the winter months.
A sunny, southern exposure will also create high temperatures during the daytime and steep temperature fluctuations at night. That, and the lack of humidity in the sun porch where I had my rosemary, did it in.
Now we know what we know. Light isn’t the only consideration for your houseplants during the winter. Sometimes it’s better to sacrifice a little light — or better yet, control it! — to get the right balance of humidity, light, and temperature.
And don’t forget to hold the water. Don’t just stick your finger in the topsoil and see if it’s dry. Lift the plant, pot and all, and give it a good weighing in your hands. It will be at its lightest when the soil is completely dry. Only then should you give it some water. Letting the root ball dry completely helps stop one of winter’s biggest problems: root rot. If only my friend’s friend had known.