Temperatures and houseplants

Don't make your houseplants shiver this winter.

The last time I recall temperature  being an issue with houseplants was back in the oil-embargoed, recessionary 1970s. But with heating fuel costing much more this winter and families cutting back on expenses across the  board, it looks as though indoor plants are going to have some cooler days -- and nights -- ahead. Is this good or bad?

It depends on how low you plan to set the thermostat and what kinds of houseplants you're growing. The ideal range is 70 to 80 degrees F. during the day and 60 to 68 degrees F. at night, says the Texas Master Gardener Handbook.

But most houseplants are adaptable. Although they may not be happy at 55 degrees F., they'll survive. Others suffer damage when they are forced to shiver.

But other indoor plants -- cyclamen and florist azaleas, for example, both popular at holiday time -- actually need to be in a chilly room (45 to 55 degrees F.) and fade quickly if they aren't.

And did you know that one of the main reasons orchids grown as houseplants fail to flower is that they require a 10-degree F. drop between daytime and nighttime temperatures?

Actually, cacti like cool winter temps, too, because they generally don't bloom in spring if they've been forced to grow year-round. For that reason, many growers keep cactus plants in a sunny spot where it's 43 to 53 degrees F at night from the end of October until early March.

There are three things to watch out with temperatures and houseplants, particularly if you turn your thermostat way back this year:

Plants on windowsills: Depending on if you have double-paned glass or storm windows and  how tight the windows fit in their frames, a windowsill can be as much as 30 degrees F. colder than in the room.

That's especially true if the plant is placed behind a curtain or sheer drapery (never a good place to put a plant in winter if you live in a cold climate).

The other problem for houseplants on windowsills in winter comes when they touch the glass, which can be very cold at night. Often that leaf reacts by turning brown.

What happens when you're gone: Most of us keep our houses or apartments colder when we're away -- visiting family over the holidays, taking that winter vacation -- than when we're home. So if you have plants that need you've learned need warmer temperatures, group them in the room that's typically the warmest before you leave.

Watch out for drafts: You know to avoid placing plants near a outside door where they receive a blast of cold air every time it's opened, although it's such a temptation to put one there, because a hall table holding a lovely plant is so welcoming to guests.

Too much heat isn't good either: Also watch out for plants that are in places where they'll will get blasted with dry heat from radiators, space heaters, wood stoves, or fireplaces. The results will be more brown, falling leaves.

The basic rule is: Avoid too much variation in temperature, if possible

Tomorrow's post will give a list of the preferred temperatures of some common houseplants. See you then.