Semi-tropical natives such as dahlias, gladioli, begonias, canna, caladium, elephant ears, oxalis and other tender summer-flowering bulbs will not make it through the winter outside of the warmest climate zones.
Tender bulbs can be either treated as annuals and composted or tossed out, or they can be lifted and stored. This depends solely on your preference. Some gardeners can’t be bothered (and some bulbs are inexpensive). Others love to baby their bulbs and tuck them away for the winter.
For those who like to keep their bulbs from year to year:
- Tender summer bulbs should be left in the ground until frost blackens the foliage. (This is true for all except tuberous begonias, which should be dealt with before frost.)
- Carefully dig up the bulbs, being careful not to damage them. Cut off excess foliage and brush off loose soil. Set the bulbs out in a warm, dry place with good air circulation to dry for a day or two. When dry, brush off remaining soil, being careful not to bruise the bulbs when handling, as this promotes mold.
- After the bulbs are dry, cut off any remaining foliage and pack the bulbs in a few layers of an appropriate "medium" such as perlite, vermiculite, cocoa hulls, clean sawdust or peat moss.
- Store in a container, with layers of bulbs separated by your medium of choice in a dry place until spring. Optimal storage temperatures vary for different bulbs, but typically range just under or over 50° degrees. Don’t worry yourself needlessly — few people have temperature-controlled storage areas — store your bulbs as best you can.
A few notes: dahlia stems may have water in them. Hang them upside down to drain. When digging gladioli, you'll notice that the shriveled old corm is there, replaced by new corms. Separate the corms. Out with the old and store the new.
Remember, not all summer-blooming bulbs are tender. Lilies, for example, are winter hardy. So are alliums. Hardy summer bulbs, like most of their spring-blooming cousins, are perennial performers and can overwinter in the garden.
Storage Temperature for Summer Bulbs
For storage, temperatures and moisture conditions vary for each type of bulb. For some bulbs, the precise storage conditions are known, for others not. When grown in containers, it is usually best to keep bulbs in the pot and store the pot under the correct conditions. Here are some tips by variety:
Achimenes - Leave rhizomes in container, dry out planting medium, and place at 60-70° F (16-21°C).
Agapanthus - Two overwintering options are possible, depending on the variety. They are:
1.Leave fleshy rhizomes in container with slightly moist planting medium and place at 35 to 55°F (2-13°C).
2.Place container in cool. 35 to 55°F [2-13°C], greenhouse and water sparingly during the winter. Return to growing area in spring.
Amaryllis belladonna - Store bulbs in container at 55 to 70°F (13- 21°C).
Anemone coronaria (St. Brigid and De Caen) - Store tubers dry at 50 to 55°F (10-13°C).
Begonia (Tuberous Hybrids) - Harvest the corms in fall, and store in dry peat at 35 to 40°F (2-5°C).
Canna - Harvest rhizomes in fall, and store in dry peat or vermiculite at 40 to 50°F (5-10°C).
Crinum - Store bulbs in slightly moist sand at 35 to 45°F (2-7°C). If grown indoors in a container, place in a bright, cool [55°F, 13°C] night temperature room.
Crocosmia (syn. Montbretia) - Store corms in peat or vermiculite at 35 to 40°F (2- 5°C).
Dahlia - Harvest tuberous roots in fall, keep away from drafts, and store in vermiculite or dry sand at 35 to 45°F (2-7°C).
Eucomis - Store bulbs dry at 55 to 58°F (13-20°C).
Freesia - Store corms or containers dry at 75 to 85°F (25-30°C).
Galtonia - Store bulbs dry in vermiculite at 60 to 75°F (17-23°C).
Gladiolus - Harvest corms after foliage dies. Store dry in mesh bags 40 to 50°F (5-13 °C). ]
Gladiolus callianthus (syn. Acidanthera bicolor) - Harvest corms in the fall, dry, clean carefully, and store at 55 to 70°F (13-20°C).
Haemanthus - Bring containers indoors and either store dry or continue growing at 55 to 65°F (13-18°C).
Hymenocallis - Place container-grown plants indoors and grow them at 55 to 65°F (13-18°C). To store unplanted bulbs, harvest them carefully leaving soil around the roots, and store dry at 60 to 70°F (16-21°C).
Ixia - Store corms dry at 68 to 75°F (20-25°C).
Liatris - Store corms in moist peat at 35°F (2°C).
Lilium - Better to leave in the ground, but can be stored in moist peat at 35°F (2°C).
Nerine - Store bulbs dry or in container with ventilation at 35°F (2°C).
Ornithogalum (Tender Species) - Store bulbs dry at 70 to 80°F 21-27°C.
Oxalis (Tender Species) - Store rhizomes or bulbs in peat or vermiculite at 35 to 40°F (2-5°C).
Ranunculus - Store tuberous roots dry at 50 to 55°F (10-13°C).
Sandersonia aurantiaca - Store tubers in vermiculite at 55°F (13°C).
Schizostylis - If stored place rhizomes in moist peat at 45°F (7°C). However, it is preferable to let them perennialize.
Sparaxis - Store corms dry at 65 to 75°F (20-25°C).
Sprekelia - Store bulbs dry in peat or vermiculite at 40 to 55°F (5-13°C).
Tigridia - Store bulbs in peat or vermiculite at 35 to 40°F (2-5°C).
Veltheimia - If possible, do not store bulbs. If stored, keep dry at 75°F(25°C). When bulbs are in containers, take indoors for winter at 50 to 60°F (10-16°C). Blooms in February.
Zantedeschia (Calla Lilies) - Store rhizomes or tubers dry at 50 to 60°F (10- 16°C). Take care not to injure the storage organs.
Zephyranthes - Store bulbs in peat or vermiculite at 50 to 60°F (10-16°C).
Courtesy of the International Flower Bulb Center (www.bulb.com)