You wouldn't think that the dead of winter would be a good time to sow seeds. But it is, for plants whose seeds need some kind of long-term treatment before they will sprout.
Such is the case for the tree peony seeds I recently planted. Well, "planted" may not be quite the right word. After soaking them in water for a few hours, I merely tossed them into a plastic sandwich bag with a handful of moist potting soil. The bag will sit on the kitchen counter for a couple of months, then go into the refrigerator for a couple more.
HOLDING BACK FOR A REASON
Such treatment is needed because tree peony seeds must lay down roots before any shoot growth takes place. To grow, the roots need some rain (or a good soaking) to leach out inhibitors, and some warmth.
The shoots, however, won't sprout until they've been exposed to a period of cool, moist conditions — outdoors or in my refrigerator. Under natural conditions, all this might take two years. In my house, all systems should be go by spring.
Lily and viburnum seeds also respond to this treatment.
For tender young seedlings, a reluctance to sprout as soon as they hit moist soil often makes sense. In a climate characterized by cold winters and periodic drought, a wild tree peony seedling does well not to rear its head until it's sure that winter is over and it's got the support of an established root system.
DORMANCY REFLECTS NATURAL CONDITIONS
Other germination quirks reflect other natural environments. Some seeds have a double dormancy, one for the seedcoat and one for the embryo. Still others — goldenseal, for example — ripen with underdeveloped embryos. That warm then cold treatment also prepares seeds with either of these quirks for germination.