cal

I do too, as soon as I see the first seed sprout, they are out in the sun all day.
We are way above 48F down here, and the suns a lot stronger too.

I don't even own lights.

Corrie

While I'm pleased you've never experienced it and hope you never do, both sun and wind burn are very real problems for many of us with young seedlings. What a hardened-off plant in the garden will tolerate quite well can be death to young seedlings regardless of the environment in which they were grown. For this reason, the standard hardening-off process calls for brief exposure and out-of-direct sunlight until the plants become adapted.

Please keep in mind that growing in Florida and California is very different from what many of us in other parts of the country have to deal with. So, artificial environments of various types are not optional for us. ;)

For a direct in the garden seeded tomato it would be in the sun from the day it sprouted, right.

True, IF you know of anyone who actually does that - direct seed in the garden.;) For the vast majority of us that simply isn't possible, much less practical.

Dave

So, I think I let a few of my seedlings get sunburned. The larger leaves are whitish looking. Will these plants recover? Will this have a negative impact on their ability to produce long-term? Any kind of first aid I can offer them now?

Thanks!

I let my tomato seedlings get sunburned too. I was behind in my plant out schedule and rushed them. They have been out for just over two weeks now and have flowers and are doing well. So there is hope.
As the leaves that got sunburned shriveled and died completely, the new top growth kept growing and was fine.
I can't speak to the long term production.

Snowman

So, artificial environments of various types are not optional for us. ;)

Yeah, I don't think many tomato plants would enjoy being outside in our -20F Iowa winter nights ;) We're *still* getting nights down in the low 40s, and we're halfway into May.

The real issue is not "too weak" lights, but lights without much UV. It's just like with humans -- when you're exposed to UV a lot, your skin tans, and it becomes harder to get sunburned. "Tanning" is your body discovering, "holy heck, I need to produce melanin now as my skin cells are dying!"; melanin absorbs sunlight, esp. UV. Plants are the same way -- they have their own natural sunscreens. If you don't give them UV indoors, they see no need to waste energy producing these chemicals and will instead focus their energies elsewhere. Put them outdoors in full sun without this kind of protection, however, and it'll do a lot of damage.

I have heard from a reliable source that one of the reasons tomato leaves sunburn when suddenly exposed to full sunlight is that this exhausts the sugar in their leaves as photosynthesis goes into high gear.

Recommended for trial: spray leaves with sugar water the night before exposing to sunlight. It's supposed to work. I don't know the concentration, but I would imagine that you wouldn't need a very concentrated solution. I've tried it before with quite dilute sugar water (barely sweet) and I can report that at least it didn't hurt the plants. Don't know if they would have sunburned without it, as I didn't utilize controls. Dilute corn syrup would probably work, too. I think of it as just a little insurance. Gradual exposure is the best option, I think.

In the future, I might also try a touch of vitamin C as a sunscreen, too. Not much.

I also set my tomato seedlings with only the coltyledons sprouted directly in the sunlight and bring them in at night when temps fall into the 40s or below, have done it for years without any sunburn problems. I transplant them immediately after germination into a larger container, an 8-inch cup at the very least and preferably larger so the soil doesn't dry out so quickly. I don't start my seedlings "early" but rather what some people would consider to be "late", or at least "on time" -- about six weeks before the anticipated last frost date.

Though I know some wouldn't risk it, I began doing it because of space constraints under lights and with the heating pad in the space I have.

But a strong warning here. This works ONLY in areas where early spring daytime temperatures are balmy. At this latitude my deck is. It's protected from wind, too. I suspect that if I winter-sowed my tomatoes on the deck, they'd probably germinate at about the same time if I brought them inside on cold nights.

Occasionally I'll plant seedlings and keep them under the lights if it's just too cool to put them outside when they germinate. Any tomato plants that develop leaves under inside lights MUST be hardened off before setting them out as all the experts recommend.

For the first time ever, I experienced sun/wind burn this year, on tomatoes and peppers. These plants had been in the shade for 2 weeks. They looked good so I pushed the sun exposure too far and it was windy that day. The leaves turned white but now the new growth is looking good.

I do the same thing, putting them out the day they sprout if I've run out of room under the lights. I've often wondered how long they have to be under lights to require hardening off, but it does seem like if you put them outside within the first few days of sprouting that they aren't susceptible to sunburn. More than a few days, I probably wouldn't risk it. I'm curious about the sugar water thing-- would be really helpful, if it works.

My little seedlings got sunburn yesterday on the 2d day of full sun with a little wind. I will let you know how they fare. They are Supersteak Hybrids and only have their seedling leaves showing with true leaf buds starting. Keeping my fingers crossed!

Yeah, mine got burned this year too. I'm just way too busy to move 12 flats of plants in and out every day for two weeks. I thought that I had done well by putting them in the partial share of a maple tree that was just breaking out leaves, but when moved to full sun, they got burned. They're now in a small hoop house full time, so I hope they'll be OK. The immediate problem is that I won't have much luck selling them if they don't start looking really nice in the next 2-3 weeks.

Here in Dillon, MT (5/7/2015), Zone 4b, the nighttime temperatures are still dropping below freezing (but usually 35F this time of year), but the daytime temps are getting up into the mid 70's. My belief is that the UV intensity at 5200 ft in an arid climate is much higher than it is at sea level in a humid climate. So an exposure of several hours at 75 F on a clear day is frequently lethal to young seedlings. I'm going through my second round of planting tomato seedlings due to sunburn, but this is the first year that I recognized the signs as 'sunburn' as opposed to too much fertilizer, too much water, to cool a temperature, etc.

I have got some sunburn on some of mine too. Luckily it has affected only the lower leave which I will trim them in the near future anyway. But it is better to avoid it by gradual increase in sun exposure.

Sey

Another cause of sun burn is caused by water droplets on the leaves, working as magnifiers, intensifying the heat. When you see a seedling kinda wilting in the sun. Then you pour some water on it . THAT can cause burn more than dry leaves.

Sey

Growing season here in Miami is when the summer heat breaks. I start all seeds in the open exposed to the elements. No heat mats or lights needed. What is deadly here in an unexpected rainstorm.