Did you know that if you’ve had a hard day, you should spend time with your houseplants? After all, they’re rooting for you.

Sometimes, though, it looks like your houseplants have had a hard day, too. Are your plants experiencing yellow, droopy leaves or other signs they’re stressed out? It’s not easy to diagnose plant troubles, as they rarely talk about their feelings.

The basic needs of our potted houseplants can be summarized as soil, water, light and air. The easiest part is air, which is generally fine in our living spaces, although it can be a bit dry during winter’s heating season.

When our houseplants look less than vigorous, or downright sickly, problems can usually be traced to the other three necessities: soil, water or light. Watering is our most frequent interaction with houseplants, and improper watering is the leading cause of plant illness.

When deciding how much water to apply, the rule of thumb is to add enough to thoroughly wet all the soil in the pot, every time a plant is watered. Then discard any excess water in the bottom drainage dish immediately, before it soaks back up. This drainage water can contain salts that have “leached” out of the soil, so don’t dump it on another plant either.

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The brown tips on this fern were likely caused by low humidity or salt accumulation in the soil. Michael Vosburg / Forum Photo Editor
The brown tips on this fern were likely caused by low humidity or salt accumulation in the soil. Michael Vosburg / Forum Photo Editor

Overwatering is a common problem, which means keeping the soil continually too soggy. It doesn’t mean applying too much at one time, as long as the excess is discarded. After watering plants thoroughly, allow them to dry before the next thorough watering.

Deciding how often to water can be tricky. Small pots need watering more often than large pots. Sun-loving plants in a bright window dry out faster than low-light plants in the corner of the room. Warm rooms and locations near heaters or air ducts increase water demand. Some plant types, such as ferns, prefer more frequent uniform moisture than cactuses and other succulents that prefer thorough drying with extended lengths between waterings.

To decide whether a houseplant needs watering, first observe the soil surface. If the soil is dark and moist-looking, it likely doesn’t need watering.

If the potting mix looks light in color, proceed with further checks. Insert a finger into the soil up to the first joint. If you can feel moisture at your fingertip, the plant is usually fine as is. Wait a day and check again. If you feel no moisture, water thoroughly.

Another good watering clue is pot weight, unless the plant is too large to lift. Develop a feel for the plant’s weight when dry, and again directly after watering, noticing the difference.

If in doubt about watering, wait. Few houseplants die from drought, while keeping plants too wet is a common killer.

The yellow leaves on this schefflera probably indicate the plant lacks nutrition and might benefit from repotting into a slightly larger pot. Michael Vosburg / Forum Photo Editor
The yellow leaves on this schefflera probably indicate the plant lacks nutrition and might benefit from repotting into a slightly larger pot. Michael Vosburg / Forum Photo Editor

ARCHIVE: Read more of Don Kinzler's Growing Together columns

Other houseplant ailments include:

  • Yellowing of lower leaves can signal a root-bound plant in need of repotting or fertilizing. Some leaf drop is normal, especially as plants age.
  • If the plant wilts, even though it’s wet, suspect root rot caused by waterlogged soil.
  • Browning of leaf tips or margins can be caused by hot, dry air and low humidity, which often affects ferns. Or it can signal a buildup of salts or elements, such as fluoride in the soil. Flush the soil occasionally to “leach” salts out, or repot into fresh mix.
  • Species like spider plants and peace lily are very susceptible to tip burn.
  • Lack of light can cause leaf yellowing, accompanied by spindly, weak new growth.
  • Mottled, light green leaves with pin-sized specks can indicate a spider mite infestation. Check also for light green or whitish aphids on new growth or under leaves, or white cottony mealybugs.
  • If plants are sickly, fertilizing won’t cure problems caused by insects, improper watering, poor drainage or low light. Fertilizer is for healthy houseplants, and it's best applied once a month during periods of active growth in spring and summer when days are long and light levels increase.

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at kinzlerd@casscountynd.gov or call 701-241-5707.