Winter care for your houseplants
Arctic cold has been visiting our region with lots of folks experiencing temperatures as low as -20 or colder and sometimes that was the high temperature for the day! This is certainly not very good weather for gardening, not outside anyway. But you can still enjoy your inside garden by taking care of your houseplants.
Winter can be a rather stressful time for us and for our houseplants too. Light levels are low and day lengths are short. As the heat comes on in the home, relative humidity drops. Hot and cold drafts can damage plants and insects and mites can get into your plants too.
Most of our houseplants are probably grown because they bring something green and growing into our homes. But, if you have some plants that can flower inside the home, the low light levels of winter can reduce the number of flowers you get to enjoy. My Mom usually would save some geraniums from the flower beds, pot them up and grow them on a windowsill. Their bright and colorful flowers were a welcome sight during the long winter season. Lots of people enjoy African violets which can bloom much of the winter. Orchids are my favorite flowering houseplant but I also enjoy many others. Flowering houseplants usually need higher light levels than those that just have green foliage. If you can move plants a little closer to your windows or pull back the curtains a bit, that will help but you have to be careful if your windows are drafty, frigid drafts and contact with frosty windows can hurt plants too.
You can also increase light for your plants by using artificial lights. Fluorescent or compact fluorescent lights work well. They provide the right light quality (wavelengths) that plants need to grow, much better than the old incandescent light bulbs that are now being phased out. You can simply move plants under a table lamp or use hanging fixtures above your plants. Plant shelves are available that use the typical 4-ft. fluorescent tubes with a tray to set your plants on, below the lights. Keep in mind that plants that need high light will need to be positioned 6 to 12” below the tubes to get enough light. People usually use timers to turn the lights on and off so that they come on at about sundown and off at bed time but you can even keep them on continuously to provide extra light to encourage flowering or growth.
Cold air can hold less moisture than warm air. If that colder air makes its way inside your home and it gets heated, the relative humidity level can drop to 10% or even lower. Most plants would prefer relative humidity to be about 40 to 60% for normal growth and flowering. If humidity levels get too low, the edges of leaves can turn brown, flowers may not open properly and you will probably have to water your plants more frequently because the plant will lose more water from its leaves than when the humidity is higher. Most people think that misting your plants occasionally will help your plants and raise humidity, but it only helps for a short time. You have to do it at least once an hour to really help very much. There are other, more effective ways to increase humidity around your plants. Grouping plants together helps them to humidify each other since all of their leaves give off water vapor through transpiration, this helps to increase humidity around the group of plants. Room and whole house humidifiers certainly help to add moisture to the air. But be aware that the cool fog or atomizer type humidifiers that really just spray out water in a very fine mist can leave a dusty film on plants and other surfaces as the water truly evaporates into the air, it leaves any minerals that were dissolved in the water behind. Use distilled or RO water to avoid that problem or get a humidifier that creates true steam.
The best way is to use a humidity tray. I picked up some plastic trays that fit on my windowsill. I filled them with pea gravel then add water to the tray so that it does not exceed the top of the gravel. Set your plants on top of the gravel. As the water evaporates it increases the humidity around the plants. The tray also catches excess water that might otherwise make a mess on your windowsill or table. Just remember to not let the bottoms of the pots actually sit in water because that will keep the potting soil wet which could lead to root rot.
Speaking of watering, that is the most important part of plant care that most people have trouble with. Overwatering is the number one killer of houseplants followed by under watering. Plants get overwatered when the potting soil does not dry out enough to allow sufficient oxygen into the spaces between particles in the potting soil to keep the roots supplied with enough oxygen to survive and grow. It is usually more an issue of watering too frequently or letting plants sit in water as opposed to applying too much water at one time. In fact it is important to water thoroughly so that the entire root ball and potting soil get saturated, when you water a plant, and that the excess is allowed to drain out of the pot. This will help to prevent an excess of dissolved salts in the water or potting soil from building up in the potting soil, which can also damage roots. You have probably seen some plants that have a brownish crust built up on the surface of the potting soil or along the rim or edge of the pot. That brown gunk is excess salt. It will be particularly common if you routinely allow the water that drains out of the bottom of the pot to remain in a pot saucer and the pot sits down in that leachate (the excess water that drains out). It is also more of a problem is you like to water plants from the bottom, like many people do with African violets. It is a good idea to water all plants from the top, at least once in a while.
Then, after you have thoroughly watered your plants, wait until the growing media dries out somewhat before you water thoroughly again. That might take a couple weeks for a relatively small plant growing in a relatively large pot in high humidity to a day or two for a large plant that is growing in small pot in low humidity. Plants growing in porous or unglazed clay pots as well as plants growing in a warm room or exposed to more air movement will dry out more quickly too. It takes time to get to know your plants and how often you will need to water them. Try sticking your finger down into the potting soil to see if it is dry, check the color of the potting soil or even try lifting the pot to see how it looks or feels after a thorough watering compared to after it has dried out to help you decide when to water.