It depends. You won't be able to put them out until well after the last frost, which will probably be May-ish for you. So they're going to be big when you put them out. That's not bad in itself, but you're probably going to have to move them up into larger pots to keep them from getting root bound. When you finally put them out, you'll be digging bigger holes. That's extra effort, extra space under lights, and lots of extra potting soil.

Now, the speed of growth is strongly dependent on temperature. So, if possible, cool them off. 50-60F might be wise.

I shoot for plant out when they are 4-inches tall. For tomatoes, that's three weeks at 70F. For peppers, maybe four weeks.

You are probably too early on the cucurbits though like Dan said they should still be OK but bigger than optimal. A few weeks prior to transplant is enough for those. Your timing on tomatoes and peppers is fine. Here in KC I sowed peppers on Saturday and I'll sow tomatoes this Sunday I think.

and take them off the heat mat once they have sprouted!

Ok the tomatoes are already about or just shy of 4 in tall now. The light are about 8 inches above the top of the pot. Maybe that’s too far and they are getting too lanky trying to reach for the light?

Would removing them from the heat mat and letting the plants grow in cooler soil hinder their growth process? I heard they need like >85F of soil temperature to grow.

You need to take them off the heating mat or you're going to cook the roots! They need warm soil to germinate.

You also need to start strengthening the stems by using a fan to create wind. If you don't have a fan, brush them lightly with your hands any chance you get throughout the day.

Pardon my ignorance... I just looked it up a site and it said they need those high temps to germinate, not to grow in general.

4" tall at 10 days doesn't sound good. Yes, they are probably very leggy and weak in the stem. I keep my fluorescent lights about 1" above the plants to keep them from reaching for the light and getting leggy.

Like jojo said, the heat mat is only used to speed germination on a few things that prefer warmer soil, but once they have sprouted a heat mat is detrimental.

Some pictures would help us help you.

High temperatures are not needed to germinate. You don't even really need heat mats. I do 70F without heat mats always, and it works fine, though germination does take a week. 85F is sometimes called "optimal" for fast germination, but they hardly need that. The point is, at this point, you don't want them to grow very fast.

I have a hard time believing your tomatoes are 4 inches tall 10 days after planting. At that rate, you're going to be planting out trees.

If the lights are 8 inches above the top of pots with 4 inch plants, the plants should, as LoneJack says, be moved a little closer. I'm hoping you have adequate lighting. The last thing you need right now is for those plants to be "reaching" upward.

I'm way south of you down here in Va and it's way early even for me. I'll be starting my melons & cukes indoors around Apr 5th. The main delay/problem is waiting for the soil to warm up enough to plant outside everything you listed. Re-potting will help to give you more time, but it's labor intensive and I'm lazy ;-)

Ok I guess my sense in inches were way off. I took some measurements and the tallest one was 2 inches. I adjusted the distance from the light and added a box for the plants to sit on so now it’s like 1-3 inches from the light. And you guys were right, all the pots were cooked.. they were so bone dry and lightweight. Idk how the plants were even alive but I bottom soaked them, put the heat mat away and are closer under the lights so hopefully this fixed my issue.

After they have been growing for a month is usually when I transplant into the next size pot.

As you have discovered, those peat pots dry out fast. I use plastic pots that are 4" x 6" so if you think of a waxed creamer carton or a large paper coffee cup, that would be the size, (and maybe something that you could use). When you pot up, I would peel off as much of the peat pot as you can around the bottom. When I used peat pots, I would find them, still intact, inhibiting root development into the soil.

PS If you decide to recycle used waxed cartons or coffee cups, make some drainage holes in them before planting.

Linda

Will do Linda, I didn’t know that they don’t go through the pots. Dan, since I left the pots standing on water for so long it actually saturated the whole thing up to the top. It’s still entirely wet.

So after removing the heat mat the seedlings are rather cold, I hope that doesn’t hinder their growth.

And it seems my melons have already germinated... I’m guessing these won’t be going in my garden and I have to start new melon and watermelon seeds again. Btw I started them in the click & grow lights as you can see. Its only like 3 inches in diameter and 3 inches depth. Is that too small?

Well, that's the point, about the tomatoes. You DO want to hinder their growth. What you don't want to do is permanently stunt them, and that doesn't happen until the temp gets in the 40Fs.

Cucurbits grow FAST when they germinate, so you're going to be way past 3-inch pots real soon.

Indoor ambient temperature is definitely above 60 degrees. Just their pot when I touched them was cold.

So my melons would definitely be no good for the garden? The fastest I can plant them out in my area is April 22nd according to almanac. So another 5 weeks. Should I discard them and start a new one in a week or 2?

Your only option for using those melons is to pot them up. Way up. Transplant into much larger pots. But cucurbits don't like to be transplanted, really, and many people insist that they be seeded directly into the garden. I think root damage is the risk. But if you pot up or plant out before they get root-bound, you're probably good to go.

The average last frost date is not always the best indication of when to plant out, especially with the hot season crops like tomatoes, peppers and cucurbits. They all want warm soils to grow - 60F most desirable. And that does not always coincide with the last frost date! My average last frost date is the end of next week but soils here are not warm enough to plant out these crops until mid May at the earliest.

btw, as one with no facilities or space for indoor seed starting, I purchase and plant starter pots and I've not had issues with growing squashes and other cuc's started in this manner.

Yes, I should have admitted that I always start cucurbits indoors. My point was that you have to be careful in transplanting them. The roots are fragile.

As to soil temps compared with last frost date, it depends. There is a nice website that can be used to assess and predict soil temps - https://www.greencastonline.com/tools/soil-temperature. I believe they do this by integrating air temperatures over the time required for conduction into the soil. I see that in New Jersey, looking at average soil temps, chances are that your soil temp is above 60F at the beginning of May.

Well then that‘s another 1.5 months until I can plant then. Looks like I definitely have to repot my melons and watermelons. I like using peat pots for the cucurbits for that very reason that they don’t like soil disturbance. Like labradors said I’ll just remove the bottom piece of the pot and plant them straight in the ground.

^^^ Remove (peel away) the collar too as this can act like a wick if it protrudes above the soil surface.

My melons are already growing true leaves. In about 2 weeks repot?

And I think next weekend I will start all my cucurbit seeds, probably the optimal time for it right?

Think of the root system as extending at least as far out as the foliage on top. By that measure, judging by your picture, you need to pot up now. These guys are going to grow fast. I'd be looking at at least a 6-8 inch pot if we're talking about planting out in a month. Three inch pots are pretty small, especially if you're going to keep two plants, but you might get by with three weeks of growth before planting out.

This can’t be good.. my tomatoes are already growing roots out of the pot and I still have 5+ weeks until I can plant outside. Pretty soon the pots will explode and will be potless!

Well, it's what we predicted long ago. You need to pot up. Maybe into some pretty big pots. Ideally make it cooler. Now, it's not as bad as you think. In peat pots, roots will just fly right through them and stick out in the air. In more solid pots, the roots will just wrap around inside, and you wouldn't even notice. Of course, planting out larger plants, you'll just have a head start on productivity.

Now, a more unconventional approach would be to seriously trim the foliage back. That will slow down the explosion of roots. Especially if you trim back the roots as well, when you pot up, things will turn out OK. All a tomato seedling really needs is a bit of stem and a few roots. That's called a cutting.

So then can I repot with the whole peat pot itself into another pot? Or does that only work for direct in ground planting? I don’t think it matters but just want to be safe as it’s too late for me to start more tomatoes seeds at this point.

Hmm. So just top them off? Or trim just some of the side branches?

Repotting the peat pot should be ok, but I'd trim off as much of the surrounding peat carefully as possible. Remove the upper collar and tear away some of the sides and bottoms while avoiding any root disturbance as you can. Each new pot/container should be at least 2x the size as the original peat pot. Personally I wouldn't do any trimming, at least not until you see the results of re-potting.

Here is my melon when I pulled it out of its 3 inch pot 2 days ago to repot it. Just barely safe I think. Slightly rootbound but I didn’t want to touch it because I know they won’t take it too well. I repotted it in giant(I think 6-8 in) pots, hopefully they don’t go rootbound before I plant them out in May.

More than slightly rootbound. Those are roots I see wrapped entirely around the small pot. But good luck.

Update: Melons and watermelons have become monsters after repotting. Both have already grown their roots out of the holes in the pots and my watermelon is forming flower buds already. I still have aboit 2 weeks I can plant them? Do you think they will survive being planted that big? Becoming more and more worried...

Well, you planted early, and now you're paying for it. Yes, they will survive, but they've been stressed. Might well not get them to produce optimally.

I have no experience of melons or watermelons (too cold here). But I can say that cucurbits such as squash and zucchini are routinely started indoors here because the ground won’t be warm enough to direct sow until late May or June. They do transplant successfully. So I think you can plant them out quite large and you'll get a crop. Maybe you can start warming the soil outside by covering it with clear plastic. You could also start hardening the plants off by putting them out during the day. And you might be able to plant out a little earlier if you use cloches or covers of some description.

Yea I have grown melons, cucumbers, and watermelons from seed in pots before and transplanted successfully in the past. So I finally planted my melons and watermelons outside on Sunday.. not knowing we are going to have low 46 F temps for four consecutive nights starting tomorrow. I was thinking of covering them with buckets for the night, will that help? Also it has been raining since yesterday and then all day tomorrow as well. If I bucket over them, will that trap moisture and promote diseases that way?

One other thing is, two of my watermelon terminal stem broke off in the process of trying to take them out of their pots. Will that cause any long term health issues, or will it keep growing? Here is a pic of my planted melons and second pic is my broken off watermelon.