Answer: Spring-flowering bulbs require a prolonged winter chill before they'll grow roots and foliage. Putting them in the refrigerator will accomplish this. (The length of the chilling period differs from bulb type to bulb type, but it ranges from 6-12 weeks.) After the prescribed chilling treatment, plant the bulbs in pots and place the pots outdoors. (The bulbs will need this additional period of cool and dark conditions in order to develop roots.) Keep the soil in the pots moist. Once the bulbs begin to sprout and the tips of the foliage are about an inch high, you can bring the pots indoors to finish forcing the plants, or you can allow them to stay outdoors. Planting in pots is a neat trick because you can unearth the pots when the flowers are spent and allow the foliage to yellow and die down in some out-of-the-way location. If you take the pots indoors, try to them pots in a cool location. If the temperature is too warm, the foliage will grow too rapidly and be pale and spindly.
Dahlias are not particularly suited to forcing. Plant the tubers outdoors in late spring or early summer when the soil warms. They need to be planted deeply and they'll probably need a support stake, as well. Wait until the buds on the tubers show, then plant them outdoors.
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