Over-Wintering Tender Plants

Darcie Boschee, KC Master Gardener 2003

Fall is soon approaching, and you have generous baskets of geraniums, copious coleus, bountiful begonias, and fantastic fuchsias. You hate to see them get killed by the frost, but what are your options? There are several things you can do to keep these and other plants going so that you can get a head start on the spring season. In addition to container plants, there are other tender perennials or hardy annuals that can be over-wintered or prepared for an early start the next year. These include plants grown from bulbs, tubers, corms, and rhizomes, and plants that can be sown in the fall to get a jumpstart on the spring growing season.

Bulbs, Tubers, Corms and Rhizomes

Plants that are grown from bulbs, corms, tubers and rhizomes include Alocasia (Elephant’s Ear), Canna, Caladium, Dahlia, Begonia tuberhybrida (tuberous begonia) and Gladiolus, among others. These tender perennials need to be dug and stored over the winter months. When over-wintering bulbs and tubers, keep them dry and stored above freezing but in a cool place. They should be stored in containers that have airflow so they don’t get moisture buildup, which leads to rotting, mold and fungus growth. In many cases storing them in plastic bins or sturdy cardboard boxes in a garage that is attached to a house will suffice. While you can store different types of tubers, bulbs, etc., together if they require the same temperature and storage medium, never store flowering bulbs in the same container as fruit because the ripening fruit puts off ethylene gas, which can cause flowering problems. Specific advice for commonly grown plants is listed below.

Alocasia (Elephant’s Ear): These are the easiest to simply treat as potted houseplants, but be forewarned, all parts of this plant are poisonous. If you have animals that eat plants, you may not want to bring this one indoors. If they are growing in the ground, lift and pot before frost. The tubers can also be cleaned and stored in dry peat, vermiculite or shredded newspaper in a cool, dry spot.

Caladium (also commonly called Elephant’s Ear, but a different plant than Alocasia): Harvest before frost and allow to dry in a warm spot. Cut back foliage after it dies. Caladium bulbs should be stored warmer than others, preferably above 70 degrees F. Pack loosely in dry peat, shredded newspaper or vermiculite. Repot in early spring about two inches deep, knobby side up. This plant really likes warm soil, so keep it moist and warm (75 to 80 degrees F). After the soil warms outdoors, you can replant outside.

Canna: You can allow frost to kill the tops, but don’t allow the rhizomes to freeze. Harvest, clean and dry the rhizomes and store between 41 and 50 degrees F.

Dahlia: Harvest the tuberous roots before a hard freeze. Brush off but don’t wash. Store in dry sand, dry peat or vermiculite between 35 and 45 degrees F.

Gladiolus: Harvest the corms after the foliage dies back. Store with good air circulation (on wire shelves or in mesh bags) between 35 and 41 degrees F.

Tuberous Begonia: Harvest after foliage dies back (after a frost but before the ground freezes). Let tubers dry, brush off any loose dirt, and store in dry peat, shredded newspaper or vermiculite between 35 and 41 degrees F. Some sources indicate a preference for a slightly warmer location, but it should always be lower than 50 degrees F.

Container Plants

Many flowering plants grown in containers can be over-wintered right in their pots. If you have a healthy plant, bring it indoors and put it in a sunny spot. If you don’t have a sunny window, you can put your plants under a fluorescent fixture, just as you would seedlings, to keep them from getting leggy. You can also encourage bushiness and prevent legginess by pinching back new growth to just above a healthy set of leaves. Before bringing any plant indoors, make sure you give it a thorough washing to prevent any pests from getting a free ride into your house. Pay attention to the lips under the container too, as spiders and other insects like to make homes there.

Acclimate your plants to the indoors slowly, much in the same way you harden off plants in the spring, only in reverse. If the plant is in full sun outside, move it to a shady spot several days before bringing it inside. Once plants are indoors, they will need less water than those growing outside, partly because they won’t be exposed to drying winds, and partly because as the days shorten and the weather cools, plants require less water. Don’t fertilize during the winter months, as that encourages leggy, soft foliage that is susceptible to pests and disease.

Plants that you over-winter inside may end up looking a little shaggy by the end of winter. That’s okay, as they will perk up once spring arrives and they are placed back outside. When placing plants outside, it may be necessary to move them to a larger pot – you may want to take a peek at the roots and see if your plant needs a new home. Fertilize lightly when you put the plant back outside, and pay attention to its water needs.

Some fruiting plants, like tomatoes and peppers, can actually be brought indoors to extend the growing season. This works best for compact plants like cherry tomatoes and small-fruited peppers like jalapenos, which can be grown in a pot from the start, and then brought indoors to a very sunny location or under a light, where they will continue to produce fruit.

Herbs especially do well in containers in a sunny windowsill. Some tender perennial herbs, like rosemary and lavender, prefer a cool dormancy period. You can over-winter those in your garage, and put them out the next year.

Cuttings from the Garden

Many annual plants including geranium, coleus (these work especially well), fuchsia, and impatiens can be started from cuttings, over-wintered, and put out the next spring with a head start on growing. Select a pot with drainage and fill with a mixture of seed starting medium and perlite. Choose healthy shoots without flowers (if possible), and with new growth. Cut 3 to 4 inches just below a leaf joint. You should have three to six nodes (points where leaves form) on each shoot. Cut just below a node. Remove the lower leaves and any flowers. Poke a hole in the soilless medium as deep as the leafless part of the cutting. Hold the cutting by its leaves and insert into the hole. Gently mound the medium around the cutting’s stem. You can brush the ends of the cuttings with rooting hormone if desired. For geraniums, it may be best to let the cuttings dry for 24 hours before potting to prevent rot. Cover the pot with a large, clear plastic bag or other clear cover and place in bright location but out of direct sun. Keep watching for root formation and once roots appear, punch holes in the bag or place the cover only loosely over the pot, allowing some air circulation. If cuttings wilt, mist them with water – you want to keep the medium moist but not wet. Pot the plants in spring and plant after the last frost date.

Sowing Seeds in the Fall

Both delphinium and hollyhock seeds sown in the late summer or early fall will have a head start on flowering the next year. Let a few of the seeds ripen on the stalks. Once they are mature, plant immediately in your garden where they will grow into small plants that will over-winter right in the ground.

Even though fall will soon be here, you can get a head start on spring by over-wintering many of your plants. Happy gardening!

Sources:

Author unknown. “Summer Flowering Bulbs: Preplant and Over winter Storage.” NC State University Extension. Undated. http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/bulbs-summer/bulletin32/storage.html

Iannotti, Marie. “Storing Tender Bulbs for the Winter.” About.com. Undated. http://gardening.about.com/od/floweringbulbs/a/StoringBulbs.htm

Iannotti, Marie. “Tips for Bringing Outdoor Plants Indoors.” About.com. Undated. http://gardening.about.com/od/houseplants/a/BringIndoors.htm

Organic Gardening Editors. “Overwintering Your Favorite Plants.” Organic Gardening. Undated.

http://www.organicgardening.com.

Relf, Diane et al. “September Tips: Perennials, Annuals and Bulbs.” Virginia Cooperative Extension. October 1996. http://www.ext.vt.edu/departments/envirohort/monthlytips/september/noteseph.html

Titchmarsh, Alan. “How to overwinter tender perennials.” Crocus Gardeners by Nature. Undated. http://www.crocus.co.uk/howto/jackfrostoverwinter/