If your house plant’s root system looks like this, it’s time, past time, to re-pot the plant. umitc/Shutterstock

Summer vacation is over for you — and for your houseplants. The average first frost date is approaching in southern Maine and has already arrived in some parts of the state.

Botanically, there is no such thing as a houseplant. What we call houseplants are mostly species that grow outdoors in tropical climates. We in the frozen North grow them in our homes because we crave greenery and occasional flowers during the winter.

Most of these plants are happier if they get to spend at least some time outdoors, where they can enjoy the sunlight, the rain, the fresh air and the summer breezes. These natural elements improve the plants’ health and give them a growth spurt.

That growth will occur in the pot, where you cannot see it, as well as in the foliage, where you can. When you bring the plants back inside, you’ll want to make sure they’re not pot-bound, meaning the roots are outgrowing their space. You can tell a plant is pot-bound if the roots are growing out of the drainage hole or if the plant is failing to take up water. Late winter or early spring is a better time to repot them, but do it now if the plant requires it.

Next, you’ll want to make sure your houseplants, like any other guests, are warm and comfortable in their new environment. Maine homes can get chilly and dry during winter. Be sure the rooms where you keep your plants are free of drafts and give them at least three hours of sunlight each day. 

The right conditions will not only ensure the plants survive their change in surroundings, but also that they have a chance to produce flowers. One plant we almost always are able to coax into bloom is our Christmas cactus. Actually, there are two species of similar plants, although they can be treated the same: The Thanksgiving cactus, Schlumbergera truncata, and Christmas cactus, Schlumbergera bridgesii. native to Brazil. Each blooms near the holiday for which it is named.

Getting them to blossom is easier for empty-nesters like my wife Nancy and me, because they require darkness for at least 12 hours a day. That may mean a guest bedroom or a room your children used when they lived at home. Some people suggest removing light bulbs from the room where you put them so that you don’t accidentally give them light. That’s probably a step too far.

It also helps to keep temperatures cooler at night, below 60 degrees, but that is something most Mainers do anyway. Cut back on watering the plants until the first buds appear. Despite their name, they aren’t cacti but succulents, another plant that does well in dry climates. Once the buds appear, you can bring them out into warmer rooms where lights come on and water them occasionally.

Our Clivia enjoyed being outside so much, it decided to bloom for us. Nice! Photo by Tom Atwell

One plant Nancy and I always hope will bloom is Clivia. We have three of these South Africa natives in our home. One came from Nancy’s grandmother when the roots of the original plant grew so large the pot broke. She gave us a division when we helped her replant the original. It has dark green strappy leaves and orange blossoms. Another, with wider leaves and paler orange blossoms, we purchased. Early this summer, a reader who knows a friend of ours offered me a white Clivia after he did a division. The division confused the plant, as both the original plant and our division blossomed — the flowers are pale yellow — early this summer. Encourage Clivia blossoms by providing cool temperatures and limited watering from when the plant is brought inside until buds appear, usually in December.

A showy plant we occasionally get to bloom is bird of paradise, another native of South Africa. It also spends summers outdoors. Once we bring it inside, we water it only when is is very dry. It likes temperatures a bit warmer than many Mainers keep their homes. We have gotten ours to bloom, but fewer than half the winters we’ve had it.

Some people buy amaryllis bulbs, enjoy the blossoms for one year and then throw the plants away. But you can get them to re-bloom. We’ll leave them outside until temperatures drop to the mid-40s consistently, and then bring them into the cellar, maybe even the bulkhead area, for eight to 12 weeks.
At that point, you should bring them out to your living space and start watering. Some, but not all, will have shown growth while in the dark. Expect to wait about five weeks for blossoms.

That’s my advice for winter blooming of house plants. Now, the shoe is on the other foot, so to speak: We need some advice.

We have an evergreen agapanthus we bought online four years ago. We have followed the instructions that came with it, leaving it outside for the summer and bringing it indoors when the weather gets cold. Yet, we have never had flowers. Not once. Please email me if you have ideas about how we can get it to bloom.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com.