Momstar: I'm no expert, and haven't used clamshells, but I remember an issue with soil depth--maybe they are too shallow? You need 3-4 inches of mix.

I've used them in the past, and if they are the deeper ones (the ones that hold grapes) they will work, BUT you will have to cover some of the holes with a bit of duct tape, to be sure the soil does not fall out, and the tape can be easily removed when the weather warms up in the spring for more ventilation.

Alberta

Too small, too shallow, too many holes, dry out to fast, no headroom for seedlings... Milk jugs and 2 liters are my containers of choice.

Karen

what karen said....

OT: Now I know what people mean by clamshells. I have been thinking this entire time people were talking about clam shells you know like oysters, lol.

Raising my hand in agreement with Karen as well - milk jugs & 2 liters hold enough growing medium so the seedlings develop the most AMAZING roots + plenty of headroom for the leaves & stems. Healthy roots + well-developed stems & leaves = winter sowing success.

I should of mentioned I also thought about using the "clamshell" that I got blueberries in for a wsing container, I thought against it cause of the holes in the bottom. They were to big, if some way like suggested above closing the holes up some, I believe they would work great. The one I am talking about could hold 3 inches deep of soil easily.

Here is a thought, if you can put soil in a container tap it, add water and the soil not come pouring out and there is only a steady drip action, not a fast pour of water, then I think it would be appropriate to grow in.

While I've never had good luck with the clamshells that strawberries and grapes come in, I've had great luck with the bigger salad bar clamshells. They are just barely deep enough (I don't use them for trees, but foxgloves, jacob's ladder, columbines etc do great). Of course, they don't have drainage/vent holes to begin with. I cut four very small holes holes on the bottom (one on each side) and three or four small vent holes on the top.

The difference is the produce clamshells have a lot of vent holes and they don't tend to be very long and wide, so they dry out quickly. The salad clamshells are about 8 X 10.

The thing I like about the salad clam shells is that I can open them to vent easily and shut them back securely just as easily. In my area (Md./DC), spring can swing from 75 degrees to below freezing or even a March/April snow or flooding rain and back in the space of a week. It makes it easy to deal with don't cook the seeds/seedlings/don't drown/freeze the seedlings. Then its easy to rip the lids off once all of that stuff settles down.

The guy who owns our cafeteria at work sells me 50 salad trays cheap every winter.

But I happily use kitty litter containers and 10-16 oz cups in catering trays too. I sort of fit the container to the type of roots and height of the plants, especially if they hace a tap root.