Although they're outside, maybe you need to look at how much sun those huge planters are getting in the winter, Debbie. They need to get cold and stay cold.
If they are on the south side of your house, or some other protected spot, (microclimate) they might warm every sunny day. That might be keeping them too warm through the winter to really chill the plants. They also might break dormancy early, so the cold period would be too short, possibly?
If this is the case, shading, (a white or silver reflective tarp?) or moving them to the north side of the house or somewhere else shady so they'll stay cold for a long time would help. When it snows, then melts, look at where the snow stays the longest. That's your cool spot! IF you need to water them, use a watering can with some ice in the water to keep the soil really cold. A drench of 70deg. water from the indoor tap can really raise the soil temp.
