Take Tropicals and Houseplants Inside (and which ones can you save?)

October 1, 2011

A mandevilla will continue to flower for quite some time if brought inside before frost and kept in a bright window.

Excerpted from the Buffalo News garden column by Sally Cunningham, September 16, 2011.  You can read Sally's columns every Friday, third section, front page.

As summer wanes, gardeners are patroling their decks and gardens with sad, puzzled faces--myself included.  The houseplants have never looked better, green and lush from a wonderful August with cool nights and enough rain.  The annuals and tropicals--petunias, geraniums, salvias and mandevillas--are bursting with flowers and buds.  I'm sad because I don't want it to end, and I know I can't take the whole garden inside for the winter.  Some of these tender plants will have to die with the first frost; others just a while later.

What's puzzling is this question:  Which ones make good houseplants and how can I choose?

Adding to the confusion is the great number of annuals, tropicals or tender perennials we now grow in our containers and gardens.  The gardening world has exploded with ever-improved cultivars that offer more flowers, larger blossoms, more exciting colors and foliage, and longer performance.  (Just take a look at the Ball Seed demonstration beds at the Buffalo Marina, for a glimpse of the industry movement to provide us with more and better selections).

This variety makes for complicated choices in September.  In earlier decades we simply said good-bye to the petunias, marigolds, spider flowers and cosmos (not successful indoors), and maybe toyed with keeping some geraniums and impatiens.  Now we face a plethora of plant names we've just learned and have to figure out which ones to winter over, and how.  My own deck and gardens have 39 different houseplants, annuals or tropical plants in containers (six over 5 feet tall), and they won't all fit in the house...and I am just an average plant collector and container gardener in some gardening circles.

Traditional Houseplants

The first group of plants that obviously go back inside are the traditional houseplants that we have used for decades, such as Schefflera, Dracaena, Ficus, snake plants, spider plants, ferns, palms and philodendrons.  Norfolk Island pines are now familiar.  Most of these plants are grown for their foliage, but a few also flower--begonias, Setcresea and Pathos.  They survive in our homes because they tolerate relatively low light, even if they do best in bright, indirect light.

These traditional houseplants thrive during the cool nights and mild days of early autumn but are damaged by frost, so watch the weather and be prepared to protect them. Ideally, we should move them inside before the furnace is turned on so they hardly notice the change.  The indoor environment in most homes is imperfect or barely tolerable for most plants, with lower light, less humidity, and higher temperatures than they prefer.  The more gradual you make the transition, the better.  And no matter what you do, many plants drop some leaves in response to indoor conditions.  Ficus plants, especially, react to any change by dropping all their leaves; don't worry--they'll grow more.

New Container Annuals

Some flowering annuals (or tender perennials) entered the green scene sometime in the 1990s and have become familiar to most container gardeners.  Among them, million bells, improved petunias, sweet potato vines, verbenas and other full sun plants are not worth taking inside.  But others do quite well if you have bright windows or supplemental plant lights--geraniums, impatiens, and coleus.  Keep dead-heading and fertilizing, and you'll have color through the holidays.  (Do let them rest a bit, with less fertilizer and water, during January and February).

Plants that are labeled for Part Sun or Part Shade typically do well inside also, including Oxalis, Streptocarpus, Streptocarpella and Maracas.  Most begonias are in this category, and it's always worthwhile to save the gorgeous dragonwing types--either the whole plant or just a few cuttings rooted in houseplant mix.

Some plants that we use as foliage plants in containers--our "spillers" or "fillers"--also perform nicely indoors, given decent lighting.  Plectranthus, Cuban oregano, the sedum called "Sea Urchin" and the cute little "Mezoo" all keep well, and you'll have a great start on the containers next May.  My current favorite, going on its third season in the house, is Plectranthus 'Frosted Jade', because of its fragrant foliage.  Many specialty geraniums are in this category too--fragrant, with prettily-patterned leaves.  For fragrance, I also keep a lemon-scented salvia with gold leaves going, even though it looks dreadful by March.

True Tropicals

Folks who have a Florida room, sun room or conservatory can pretend it's always summer, with hibiscus, lantanas, passion flower vines and mandevilla flowering continuously.  Most of us have to compromise by taking these plants in for a while and then letting them go dormant.  You might be surprised, though, how long the mandevilla or dipladenia keeps flowering with supplemental indoor lighting or a bright window.  Best recommendation:  Enjoy these tropical flowering plants as long as they keep flowering, and then cut them back severely.  Retire them to a cool room with some light, but don't let them dry out completely.  Introduce more light and water in late winter, and begin to fertilize as they begin to grow.  (An alternative--cutting them back and putting them in the basement to go completely dormant--can work.  But most basements these days are entirely too warm.  Temperatures above 45 but below 60 degrees are ideal).

Sanitation

I have heard plant advisors recommend all sorts of spraying, dunking, and showering before taking plants indoors.  If you have a precious collection of indoor plants, you may take extraordinary measures.  Frankly, I think that it's usually enough to perform a good plant inspection, remove the debris in the pots, and brush the pillbugs off the container bottoms.  Typical houseplant problems sometimes develop anyway, no matter what you do now, triggered by overly heated, dry conditions and plant stress.  Experts know that certain species develop certain problems (fuchias get thrips and hibiscus get whiteflies).  Later in the season we will address all these.  But for now, the challenge is making your choices.

Which ones will you take inside?  Personally, I'll probably squeeze all 39 in.  The sofa will just have to go.