Homestead's gardening educator did some teaching at the December meeting of our Golden Spades group and the topic of houseplants couldn't have been timelier.   As he told us, "Winter is the most misunderstood season for houseplants."   But in short order he made sure we understood how houseplants grow - so that his tips for their care would make sense to us.  Cool.

Where Houseplants Come From

To find plants that survive indoors, where the conditions basically never change, you have to go to the part of the world where conditions are similar to our living rooms all year round.  That magic area is anywhere near the Equator, where it's summer all year long with long, warm days.   The Tropics.   Some plants from the  nearby Subtropics can also be grown in our homes - plants like Christmas cactus and poinsettias.  In the Subtropical zone, temperatures are warm but they DO drop at night.

Growing Tropical Plants Indoors

So, how do tropical plants respond to being grown in our homes in the winter?  First, they're not used to the reduced sunlight, so as the days grow shorter they react by dropping some of their leaves – the older ones.  A ficus, for example, will lose 50 percent of its leaves in winter, in order to reduce its need for light.  See, supplying food to all those leaves is a burden in periods of reduced light.

But that's not all.   Tropical plants also adapt to low light by reducing activity until the situation improves in the spring.  Come to find out, plants put out new growth in spring and summer not because of warmer temperature as much as increased day length.  So it follows that official start dates for each season correspond to longest and shortest day lengths, not to highest and lowest temperatures.   Interesting!

  • Avoid overfeeding houseplants in the fall, winter, and early spring by reducing the fertilizer to ½ strength and applying it half as often (once a month is fine).   Full fertilization would risk salt build-up in the soil, which burns the roots.  In our area, use this reduced-feeding program from November through March.  Two products Gene likes are Jack’s Classic and Miracle-Gro, both balanced, water-soluble fertilizers that run out the drainage hole, which prevents that salt build-up in the soil.  They also include the minor nutrients, not just the big three.
  • Keep plants away from drafts.
  • The watering needs of houseplants at the root zone don't change much in the winter, but some plants (like for orchids and bonsai) really appreciate a boost in humidity, which can be accomplished by using a simple "humidity trap".   That's just a flat pan with ½ to 1 inch of pea gravel on the bottom, on which the plants sit.   This evaporation-producing technique is a better idea than spraying water on plant leaves, which can be an invitation to plant disease.
  • In winter, hold off on major events like cutting back, trimming, and repotting.  Pruning can be started again in early spring (March, here in Maryland).

Good news for aspiring orchid-growers.  If you've heard how "temperamental" they are, Gene hopes to disabuse you of that notion.   Beginners should choose "coolhouse orchids" that don't demand constant heat and humidity, like the hothouse orchids do.   (Then it almost goes without saying that we can't mix the two types in the same growing situation.)

Are Indoor and Outdoor Bulbs Interchangeable?

Short answer?  No.  Paperwhites, for instance, are from the Middle East and the Mediterranean region and won't survive cold winters.   And conversely, daffodils that we grow outdoors need a cold period to survive, so won't live for long indoors.

Conifers as Houseplants?

Not a promising plant group for indoors.  Gene says "You can’t take them to Miami - they don’t snowbird."   Conifers don't just tolerate cold winters - they NEED them.

What's New in Indoor Plant-Growing

Herbs!  Herbs that we can grow indoors in the winter include basil, oregano,  and parsley.  Then just move them outside in the spring.   The herb rosemary gets woody after a few years, so Gene just starts some more when that happens.

Got Houseplant Pests?

Gene recommends Bonide Systemic Houseplant Insecticide for control of most insects (though not spider mites).  As a  systemic, it works for about  8 weeks before it has to be reapplied.  (Just don't use it on edibles.)  Another option is to use insecticidal soap, which is effective but needs to be applied more often.

Posted by Susan Harris

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