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10 Frost Tender Plants to Keep or Compost After Summer

Every fall gardeners in climates that experience true winters have a tough decision to make.  Their outdoor gardens are filled with frost tender annuals, tropicals and houseplants that are facing the end of their lives with the first hard freeze.  Do they merit a spot in the house, basement or greenhouse or should they be sacrificed to the compost pile to make rich humus for the benefit of next year's garden?

Here is a list of 10 plants that many of us struggle over what to do with as we face this dilemma.  Here the arguments are made and the judgments delivered.

1. Summer Annuals – It's tempting to try to save bedding plants such as petunias, torenias, and marigolds that have been so beautiful all summer.  The fact is annuals are named so for a reason.  They complete their life cycle in one year.     Verdict:  Compost!
2. Begonias – Begonias are an exception to the rule when it comes to bedding plants, especially unique varieties such as Beefsteak and Angel Wing.  Just dig up your favorites and plant them in pots with a sterile potting soil.  Place them in a room with bright morning sun and water when the soil is dry.  They may look a little rough, but they will revive next spring.  Verdict:  Keep!
3. Summer Bulbs – Summer bulbs such as dahlias, elephant ears and calla lilies are a toss up.  In my zone 7 garden I cover them with a heavy layer of mulch and cross my fingers.  Gardeners in zone 8 and above don't need to do anything because these plants will survive the winters.   In cold winter climates (zone 6 – 3) the bulbs should be dug after the first killing frost, and then dried and stored in peat moss.  Verdict:  Keep!
4. Boston Ferns – Personally I think Boston ferns should go on the compost pile, but I have a brown thumb when it comes to houseplants.  The dry air in winter homes is especially hard on ferns.  More often than not bringing Boston ferns indoors results in a messy pile of leaves and a ratty looking fern.  Verdict:  Compost!
5. Banana Trees – Banana trees are definitely a statement maker.  Several varieties are cold tolerant to zone 7 and can be left outdoors over winter.  The top will die back after the first hard freeze, but will sprout new growth in spring.  To protect the roots from freezing cover the soil with 1 foot of mulch.  In colder climates you will need to store your banana trees indoors during the winter. If it is planted in a bed, dig up the plant before the first frost. Gently remove any excess soil and then cut the leaves back close to the base of the trunk. You will be left with something that looks like a pole with roots.  Place the plant in a container filled with moist sand and store it in an area that will not drop below 50 degrees F. Stop watering or fertilizing the container and allow the plant to go dormant. If your banana trees were growing outdoors in containers and they are a manageable size you can move them indoors and treat them as houseplants. Just place them in a warm, sunny location, stop fertilizing and only water them as needed.  Verdict:  Keep!
6. Angel's Trumpet – Large, trumpet shaped, fragrant flowers and rapid growth make this sub-tropical shrub a definite keeper. Brugmansia can withstand a light frost, but will perish once night temperatures drop below 35 degrees F.  For those you live in an area where winter temperatures stay above 30 degrees F., they can be stored in an unheated garage or shed.  Don't be discouraged if your plants get a little scraggly looking during this period. Just water occasionally and in the spring they will come out of dormancy and start leafing out.  Verdict:  Keep it!
7. Mandevilla Vine - Mandevillas are cold hardy to zone 9, which means they need to be moved indoors when night temperatures regularly drop into the lower fifties.  If you have the space and plenty of sunlight, you can treat your Mandevilla as a houseplant.  It may go dormant anyway and lose its leaves, in which case you should cut back on watering severely to prevent root rot.  You can also keep a mandevilla in a place where temperatures stay between 55 and 60 degrees, such as a basement, crawlspace or garage.  Cut the plant back to about 12 inches above the soil and water only occasionally.  Verdict:  Keep it!
8. Bougainvillea – Whether or not you choose to keep your Bougainvillea depends on where you live.  In zones 10 to 11 bougainvilleas cycle between dormancy and active growth throughout the year and are showiest from December through June when it is cool and dry. In zone 9 they will die back if there is a hard freeze, but will return in spring. The rest of us should treat this tropical beauty like an annual and thank it for adding color to our summer gardens.  Verdict:  Compost it!
9. Geraniums – The smell of geraniums always reminds me of my mother's sun porch in winter.  Unfortunately I did not inherit her ability to care for them so my vote is to send geraniums on to their great reward unless they are just too special to let go.  In which case you can store them in the pots they are planted in.  Cut the plant back to about six inches and place it in an area with bright sunlight that stays above freezing.  Water when the soil is dry.  Verdict:  Compost it! 
10. Oxalis – It is a tender perennial that is cold hardy to zone 8, but it can be overwintered indoors quite easily. I think you will find that it is equally as delightful as a houseplant as it is in the garden.  Keep the plant in a room with bright, filtered light and low humidity. Oxalis goes into a semi-dormant period in winter so go easy on the water and don't fertilize the plant. If you would prefer, you can also dry and store the tubers.  Dig the plants from the garden and dry them with the soil attached. Plants grown in containers can be dried and stored "as is."  Verdict:  Keep it!