As long as the caps are off you don't need to remove the top. The shape of the milkjug spout acts as a flue and it rapidly vents away heated air.

I don't have an answer but I'm confused by this as well. I keep reading about new plants being burned on days that are too warm and that the lids do need to be taken off. I'm also wondering if the plants get enough sunlight through the thick walls of the milk jugs.

Indu,
Because I know where you live and how warm it is there, I'd say if your sprouts are full sun plants and have 2 sets of leaves its safe to open up the tops on nice days. Just be sure to watch them as they'll dry out in no time. Until they're stronger (older) you might want to keep the mid day sun off them for a while. You are going to be planting out in a matter of a few weeks from now. :)

If they've grown so much that they're smashed up against the tops I'd say its past time to open them up. :)

If freezing (or frost) is expected close them back up if the sprouts still fit inside the tops and they are frost tender plants.

If you're expecting really heavy rain I'd close them back up to keep them from getting flooded. (do not put the lids on milk jugs or bottles--built up heat needs to escape and small amounts of rain getting inside won't hurt them)

Homeblessings, they should get plenty of light through the containers. I don't take lids off my containers until I see at least 2 sets of leaves or its really quite warm. But where I live it warms up early and quickly.

Indu lives further south of me and in a much warmer zone, they hardly ever freeze down there in zone 9. I'm zone 7/8.

Shade plants, keep shaded of course... full sun will not make them happy.

We should know and understand what amount of sun each plant needs.
Not all plants/sprouts/seedlings require the same thing at the same time or the same amounts.

Thank you all. I do not have the caps, so I think I am good on venting the hot air out quickly. We are expecting quite a bit of rain tonight and tomm so I think I will just stay put. There was one specific sprouting that was almost 3-4" tall, I will go back today and see if it has grown even more..
I researched and wrote up notes on each of the seeds and how the plants do. I will refer to my notes and see if I need to move the jugs from their current spot. As of now they are on the west side of my house and close to the wall, they don't receive muchsunlight. Its shaded most times of the day getting maybe an hr or 2 of afternoon sun.

I am new to this, I have 3 containers planted just today. My question is: If I am starting perennials, when should I expect to take the lids off of my milk jugs? Do I take them off for the day, replace at night, if it is a very sunny but still cold day or wait until April temps? Also if I take the top half of the jug off later in the spring because plants are big, do I leave them out at night if temps are around 50 F? Should I be replacing the top half of the jugs at night?
Thanks!

garden---perennials can take the low temps at night. You only need to worry if the temps get too warm during the day.

The whole "tops on, tops off" question depends on your climate and where your jugs are located and how soon you plant out the seedlings. I am in zone 7 and have been WSing for many years. I work full time and do not have the ability to "baby" my jugs. I have had hundreds of jugs most years and while I might crack open the tape put a little stick to keep the opening circulating more air for those jugs that are my very last to be planted (and therefore waiting in hotter weather) for the most part I am moving seedlings straight from a closed (except for the spout) jug to the garden bed in May and and early June. I do not ever "saw the tops off" the jugs as I save the hinged jugs and reuse from year to year.

If you take the tops off, the question of "do I run out and put tops on at night so the seedlings don't get cold" only comes into play if you are receiving freezing temperatures. If the seeds have germinated (and they are perennial seeds)they have annouced that they are "ready" to be in the world! No pampering required. That's what makes WSing so much easier. Annuals may need some "topping" in below 32 weather, which is why I wait to make these jugs till this risk of freezing is over for my area - again I do not have time to re-top. So some of your decisions will be based on your lifestyle as well, and how many jugs you have out there.Pampering 10 might be an option, pampering 300 will stress you out!!!!

when the parade passes by and you want mardi gras beads...

oops, wrong website.

Bakemom, your funny !! I had a heaty laugh.. I'm in no rush for any of the mardi gras beads ;)

My nasturtiums, Cosmos (orange) and Calendula are upto the brim so I remove the tape and opened up the cans.. I am so excited. I am just hoping that mother nature will not spring a surprise on us and the temps goes below freezing. My next obvious question would be how close I plant them in the beds? I read about 5 - 7 together to make an impact... Any suggestions?

well, its happened.. 2 of my lobelia flats over heated just this morning. :(

I was late getting out there to take the tops off. Only lost the mass in the center though. Outside edges are still ok. It looks like I didn't lose them all. I'll be separating them this weekend.