I have a few types of plants that require cold stratification. Most suggestions I've read (including the instructions on the seed pack) say to do this in the fridge.

Since I am planning to start them in cell trays, can I simply plant them now and put them on the porch over the winter?

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I've successfully stratified buckeye nuts in the refrigerator, but they're very easy (you can actually just plant them in the fall as soon as they're ripe and they'll almost always sprout in the spring, unless dug up by squirrels). I've never tried the planting-and-leave-on-porch method. This method, IMO, has a couple of important caveats:

  1. Your porch must be completely unheated and should not get above freezing for at least three months or the cells may thaw and dry out, possibly killing the seeds
  2. Do not leave the planted cells in any sun whatsoever or they will thaw and then dry out. This will probably kill your seeds.
  3. You must protect the cells from mice. They will eat pretty much any plant material that they can get their teeth into, and there's no guarantee that your unheated porch will not have the 1/4" gap that mice can use to enter your house.

I've had good luck stratifying some liatris (L. cylindracea and L. spicata), daylilies, some asters, some primula, and Penstemon digitalis just by storing the seeds in air-tight containers in my zone 5 unheated garage, and then planting them in March in my basement. OTOH, I've had poor luck doing that with other liatris species, some primula, some alliums, and most penstemons.

I've also had some poor luck trying the standard plant-and-refrigerate method for the same plants I've referenced above, so I don't know that I would recommend it.

There is one other option, though, that I've had some success with - planting the seed now in a seedling bed (I use a part of the vegetable garden) - making sure to bury the label deeply because it will frost-heave out of the ground otherwise. The seed will naturally stratify and sprout at the appropriate time in spring. You can do both, too - plant in cells and leave on your porch and also plant in the garden. You would double your chances that way.

Unless the plant is a groundcover, I leave them in the nursery bed till the fall (if spring/summer bloomers) or following spring (if fall bloomers) and then move them to their final home.

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