Big Tender Bulbs Now

Begonia in early fall frozenQuestion: My tuberous begonias and dahlias had the tops frozen by a recent frost. Is it too late to dig the bulbs? How should I store them?

Answer: Normally, the best time to dig tender bulbs like begonias, dahlias, gladiolus, canna, calla lily, ranunculus and caladium is when potatoes are harvested (which is right now). A light frost is actually good to send the bulbs into dormancy. The accumulated heat in the soil is usually enough to protect the bulbs from freezing even though the tops are damaged.

Caladiums and tuberous begonias are the most tender. Some people dig them before heavy frost to make sure the bulbs are not damaged. You can check for soft spots which appear when bulbs are frozen. If the bulbs are firm, they have not been frozen.

I avoid washing the soil off bulbs because moisture stimulates the development of rot organisms. A brush works just fine. Bulbs should be stored in a cool, dry place where temperature will not go below freezing. Temperatures between 40 and 55 degrees work quite well. Bulbs can be stored in a refrigerator. However, they should be checked periodically to make sure packing material is not picking up too much moisture.

In our arid climate, it is important to store bulbs in dry peat moss, vermiculite, sawdust, or similar materials to protect them from excessive moisture loss. Never use plastic bags for bulb storage. Paper or mesh bags allow some air movement.

You can get a head start on most tender bulbs by planting them in containers in late March or April. Gladiolus are probably best planted directly outside in late April or May. Smaller bulbs can be planted in 3 or 4 inch pots. Larger ones should be planted in 6 inch or gallon pots. Bulbs should be planted near the top of the container so there is room for root development. Ideal temperature for starting bulbs is 65 to 70 degrees F.

Use a good quality potting soil mix. Once bulbs are planted soil should be kept moist. Wait until the top of the soil dries out before watering.

Bulbs do not need light until a shoot appears above the ground. Then they should be placed is as strong light as possible. A south facing window is best. When daytime temperatures are mild outside (above 50 degrees) pots can be placed outside. Bring them back in at night to prevent freezing.

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