I thin that for early May plant out, it i too early to start hardening off.

And If your seedling are at the size shown in your picture, they need to be potted individually. They have room to get bigger ( ~8" tall) for about 2 more weeks.

Sey.

Hardening off is normally begun approx. 1 week prior to plant out date. Those plants are still too small for hardening. If they were 60 degrees inside then 60 degrees outside. 55 is the commonly recommended minimum exposure temp. And yes sun exposure is definitely a problem. So is wind. Either can kill them fast.

Tons of hardening off discussions here the search will pull up for you to read.

Dave

Am in South Jersey, zone 7a. We place outside about May 1, and keep OUT of direct sunlight (under umbrellas) for about a week. Fine if overnight temps are at least 40+.

Next 7-10 days, we expose gradually to sun (1 hour/2hour/3 hour/etc.). In ground by May 15-20. Key is, little by little direct sun.

In my experience:

1. no hardening off is required for temperature. Either, temperatures below freezing will kill tomato plants or temperatures above freezing won't. People frequently plant outdoors at about 33 deg. F. using Wall O Water. Goggle it.

2. If the tomato seedlings were grown under sufficiently intense blue, violet or UV light, such as that from typical fluorescent, 50 watts/square foot, 16 hours/day, then no acclimatization to full sunlight is needed. Many times, I have planted my seedlings directly from artificial light to full noon sun light without serious problems.

Judging from the spindly plants in your photos, not only will you have problems with sunlight, but you will also have problems wind and rain folding your plants over. You might even have problems with birds pulling out your seedlings to use as nesting material. You could have saved yourself a lot of work and aggravation by doing it right in the first place.

I know its excitng to get close to planting out time but don't rush it. :) Your seedlings would benefit from being potted up into Solo cups (planted deeply,) and given a few more weeks under the lights with the lights just a few inches above them and a fan on to strengthen the stems. Best of luck for a great growing season!

Thanks for all the help!

Yes, there is no perfect thing. I knew quite well that I did not have perfect growing condition to start with. But the weather is warming up and I'll gradually move them to outside to get more light. Early Map is still the target.

Last year, I transplanted a lot of volunteer tomato seedlings. They were about the same size.

Then they quickly get established.

I'll be just happy to do better than that.

I disagree, I have grown under a T5 fluorescent, on a very sunny windowsill, and my tomatoes (and other solanaceous crops) will be burned after 1 hour put in the direct sun on a warm and sunny day with no other hardening off. I wouldn't go so far as a 1:1 temperature for hardening off, but some attention to the temperature is required, especially if it is windy. Wall O Waters keep the plants warmer so that isn't really a valid comparison.

You can't compare volunteers to those grown indoors. 2 different animals simply because of their totally different growing conditions.

So I have to ask - since you have already decided to do this despite the advice to the contrary (except from one) why ask in the first place? Just do as you think will work and take your chances.

Dave

Since it is 60+F outside, I'm going to expose the seedlings to outside, little by little. Also, I'll be watching to make sure they do not wilt.

Also these seedlings have been exposed to weather before, when they were much smaller.

The 38 plug trays are all I can manage. I have 200+ warm weather seedlings. Can't move all of them to bigger pots.

Thanks for the help.

I put out the seedlings out this afternoon for a few hours, half sun. They have no problem.

Keep in mind those small pots will dry out fast in the sun. It is a lot different than starting indoors.

IMHO I don't think there is anything wrong with carefully and slowly bringing them outside (following proper hardening procedures) if the weather is accomodating.

Take a look tomorrow and make sure none have developed sunburn. It may not be immediately apparent.

Also look out for bugs.

Peter, yes, I'm doing it slowly and watch them carefully. I do not want to trash all my seedlings.

But I do not have an indoor lighting system. Just not practical for the family. So I have to work out of my situation. They need light, and need to be stronger before they are set to the garden. I do not care if they are small, just should be strong. Before, two years ago, I always bought the smallest tomato seedlings from the local nursery, by the flat, about 24 plants a flat. They were about this size of plants. And I got a lot of harvest out of those tiny plants.

" Wall O Waters keep the plants warmer so that isn't really a valid comparison."

When the water in Wall O Water (WOW) begins to freeze, the temperature inside is just slightly above 32 deg. F., e.g., 33 deg. F.. The only thing I don't like about it is that freezing causes WOW to develop leaks, more trouble than it is worth.

Wind combined with either cold or too much sun can easily kill a plant--not necessarily from physical breaking, but it can dry and bleach out the foliage in a really damaging way.

Generally, you can harden off any size tomato seedling/plant. But I think smaller ones will struggle if the conditions are not ideal. So that is why I said to pot them up and keep inside for while. You should get better results this way.

Sey

Yeah, the younger seedlings are very easy to kill. You fall asleep for an accidental nap and forget to take them out of the sun when you're supposed to... Totally not speaking from personal experience here.

whatever you do, don't put them in full sun. no amount of artificial light can compare to the power of the sun. i tried going from a 600W HID lighting, to outside and within a matter of minutes plants almost burnt and wilted right before my very eyes. put a 600-1000W hid outside in full sun.. you would barely notice it's even on. here is me keeping the 600W bulb 12 inches from the tomato plant to keep it from stretching, yet the sun is 93 million miles away.. mind blowing.