If the local greenhouse's plants are still that small and since they grow with with a target date in mind, I'm guessing they consider it still too early for planting out in your area. Why not ask them for advice?

Dave

Nighttime temps are hovering between 42-48 degrees, and holding steady around there in the forecasts. The greenhouse I purchased the plants from had lots of really huge tomato plants, but just in the really common hybrid varieties. The varieties I wanted were the tiny ones. I did ask them, and they said the transplants would be fine to be put out with the Walls of Water. But even under the right temps/growing conditions, can plants just be to small to handle transplanting outside?

As to the size of the plants, while plants that small can be transplanted with no problems given ideal circumstances, your circumstances aren't ideal. I'm not sure I understand why you just didn't wait a bit until they were bigger and it was much closer to normal planting time but since you already bought them and you don't want to transplant them, which would be the normal recommendation, then I guess you really don't have much choice but to plant them out and hope for the best.

Dave

How much longer do you think I could I let them grow in their current planting cells? (1"x3")

In the end I keep getting blossom drops the first few rounds. So it was not worth the stress to plant early to lose the lower fruits.

If I had to do it though, I would use cold frame or hoop house, but nothing else.

I have some others started the same time that I waited to pot up (just this Monday) since I didn't want to leave too many trays for my dad to water while I was on vacation, I haven't seen any new growth in 3 days so I am hoping for the best as they seemed to go into suspended animation - didn't grow at all the 10 days we were gone, they were in tiny cells with Jiffy seed starter mix and I'm just hoping they aren't permanently stunted (though besides larger cells and the fertilizer, it could also be that the Espoma holds moisture better and the ones still in Jiffy may have gotten too dry while I was away). Don't want to see you have the same problem.

How many plants did you buy?

If they aren't hardened off, I'd pot them up in 16 oz cups with some mix with starter fertilizer, then a few days - week later start hardening them off, you can still use the WOWs if you already have them and nights are cold.

We usually plant out the last week of May (25-28th target) each year but lows are still averaging mid-high 40's then. The past 2 years it's been too cold and wet and I've waited til mid-June. Hope to get them out in May this year.

I was at Home Depot yesterday, they had some nice compact bushy dark green Bonnie plants (didn't look at tags) - they were the perfect size to set out, but it's way too early here. Last year they were selling tomatoes in March (when we had a heat wave - of course then we had 3 hard freezes the last week of April)!

I've heard people complain that they can be a pain to work with, but have never heard of someone losing their plants.

I, and others, don't harden off our plants when they go into WOWs.

Dave