Not sure when your last frost date is, but keep in mind that plastic does not insulate more than a couple of degrees or so at night. Also, if your soil is too cold or wet (it probably is), your peppers and melons are going to be stunted and take a while to recover even if they dodge frost. What you could do is install the hoop house, ventilating during the day to release excess moisture, to warm the soil without actually transplanting yet.

Agree with the above that you first need to build the hoop house and get the soil warmed under it. Meanwhile, yes your plants will have to be hardened off first. That is still far too drastic a change for them to go cold turkey. ;)

Once that is done and the soil in the hoophouse has warmed well then you can either plant them in it or just use it to protect them in their containers till ready for the garden.

Dave

Okay, thanks. I think I'll harden them off in the hoophouse in their containers and bring them in at night until the soil warms. I appreciate the help - I got too eager!

I'd harden them off, unless you want to learn the hard way like I did last year. It didn't take much more than 1/2 hour, if that, to cook my seedlings in direct sunlight. The specs on the row cover material I looked at say you'll get 50-90% light transmission, depending on the weight you use. And I remember reading somewhere that a good indoor lighting setup will give you about 25% of the intensity of sunlight. So, going by those numbers, you'd at least be doubling the intensity of what they're used to, if not tripling it, or more. I don't know if the intensity of different colors of light matters, but that will probably change too.

Wow, I knew that sunlight was much more intense, but didn't realize *how* much more intense. I've been babying these plants for weeks - don't want to kill them now!

Some considerations:

1) seeds that were planted in the hoophouse exhibit more hardiness to hoophouse conditions than those that were transplanted. That means resistance to both cold and heat. I assume that having roots in very warm soil is a source of hardiness for little plants.

2) I have 11 carboys (which I mostly use for winemaking) and 6 6-gallons buckets in there, full of water, 91 gallons of thermal ballast total, and I also have an inner plastic layer. Still, I only get 4F difference when the wind blows. When the wind does not blow, it is more like 10F.

3) Another 10F or so can be had by placing a milk jug, bottom removed, on the seedling, and sealing all around with mulch. That would be a third layer. A bit of mulch inside the seal will provide plenty CO2, Best done if you have drip in there. Probably it is a matter of having the seedling lying low in mulch, and a small hoophouse (the jug) with low surface, and also stopping any small draft from really touching the plant

4) some seedlings are better than others in the hoophouse. Melons are best, toms are a bit delicate. They don't really like hot.

5) if your temps are warmer than 65F, sunny, better open one side, or no seedling will make it.