What happens to my tomatos?

Question

The leaves of my tomatoes (three diverse sorts) don't look good.

On the fourth day outside (still in the process of hardening), they started to show the light yellow to brown spots on some leaves, as you can see on the photos.

They not only show these stains, but also stopped growing for already two weeks, until now.

What happened to my tomatoes and what can I do to help them?
We’ve had surprisingly clear weather, was it just too much sun?

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Additional Information

• They have lost their first pair of leaves
• I grew them from seeds.
• I used low nutrient soil from the bag for the first growing stage
• Planted in bigger pots about a week ago
• In the bigger pots I used tomato soil, containing nutrients for a couple of weeks
• Watered when needed, but before the plants showed signs
• Watered with soft water (no rainwater available)
• Watered with a watering can, right onto the soil only, no rain so far
• No additional fertilizer used so far
• No spraying with anything
• About half of them were under plastic domes outside

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Photos

Answer 1

This does look like 'sunburn'. How have you been acclimatizing? This is not a deal breaker. I've had completely frozen tomatoes that actually came back. We need more information and more pictures. What soil did you use in your pots? What fertilizer have you used? What are your watering methods? Have you sprayed your plants with anything? Answer a few more questions, anything else you can tell us is never insignificant.

Not bad so far, but tomato soil, is that sterilized potting soil?

Those domes threw up big red flags. Sunlight going through those domes can be accentuated big time. The domes just might have been your problem. Cut off the dead leaves, give your tomatoes some fertilizer. Mulch is not fertilizer. I tell everyone new at this to use OSMOCOTE 14-14-14. You will probably only have to use it once, follow directions. It is extended release, balanced fertilizer. Us humans strip away entire ecosystems without thinking all those chemicals necessary for photosynthesis are tied up in the biomass, not in the soil! All of our gardens are artificial and up to us humans to add what plants need to make food for themselves. Do everything in our power to understand what these needs are. Usually we keep adding 'goodies' like mulch, or fish emulsion, or blood meal or anything that says, 'nutrients'. To humans that is food. For plants that is simply chemicals necessary for photosynthesis. Photosynthesis is what makes food for plants. A little too much fertilizer or chemicals and you can easily kill all your plants.

Any plant grown in a pot or planter should be planted in sterilized potting soil. Do not get potting soil with added fertilizer or water holding gimmicks like sponges or gels. You want to know as best you are able what you've added for fertilizer. Tomatoes need nitrogen but to get fruit you have to keep that nitrogen lower in percentage to the phosphorous and potassium. We need to know the pH of the soil. Improper pH and the plant will not have access to certain chemicals it needs to do the work of photosynthesis even though those chemicals are right there in that soil.

Watering 'when needed' is the right way! If you have used garden soil for these tomatoes...you might have caused even more problems. All it takes is one spore, one virus to infect and kill your plants and there would be no measures to save them. Where did you get this soil? So far all I see is damage from the sun most likely because of the domes. This is the same reason to never allow fish in an aquarium to be put outside in the sun. Very quickly your fish will be boiled.

Additional:

Check out this article if you would. I don't think this is nutrient deficiency other than just not enough to be healthy and has weakened your tomato allowing disease. Check out gray mold and blight. If you see something that rings true, let me know, okay? Need to know what 'tomato' soil is. Is it from your garden or from a bag? Are they on the patio in pots? guide for diagnosing problems on tomato leaves

Answer 2

Soft water is probably going to be a big problem, due to the sodium content. This may be why your plants don't appear to be absorbing water well (and why they're so prone to sunscald). Potassium deficiency is another likely cause of the thin leaves, if you're not using potassium to soften your water (and definitely of the weak look to the plants). Potassium strengthens plants a lot and helps them absorb water (sodium can interfere with water absorption), although potassium in over-abundance may cause stunting and yellowing, too. However, if it has both sodium toxicity and potassium deficiency, I'm not sure that potassium will help in an already salty soil. I don't know, though, but people say it's a bad idea to add fertilizer and mineral salts to extra-salty soil.

The light-colored patches appear to be sunscald. A nutrient-deprived plant can seem to be more prone to stuff like that. It's possible that there are too much aridity and heat stress for the plants, too. Potassium also helps with heat-tolerance (as does magnesium). The plants may also have had low light levels before transitioning to the hardening off phase. Extra organic matter may help.

Misting your plants (not with soft water) may help their leaves to absorb more water, and may strengthen the plants, due to the wind-like pressure of the water, and due to the foliar application of whatever nutrients happen to be in the water.

Anyway, the plants look like they need extra nutrients and to adjust to the sun, but it sounds like soft water may be the main problem. Rainwater is really great for plants, but regular water (or even city water) should be an improvement over soft water. If you can give the plants new non-salty soil and turn the softener off when you water, that may help (unless the regular water kills plants). City water can be pretty bad sometimes, but it really depends. Our city water works, but plants definitely prefer rainwater or filtered water to our city water.

Too much salt may impact the roots of your plants. I had a pepper with too much salt that died of root rot. This is likely because it didn't absorb enough water (so, it got too much water in the container; you'd think salt would deter the microbes that cause root rot, but it didn't in this case). So, a drying-out plant, in this case, probably would have done better with little water (not more).

If you've been growing them on soft water all along, the salt content may not have begun super high, but may have accumulated. Salt (in the form of sea minerals, at least) can be beneficial to plants in small amounts, but in my experience, there comes a time when it's too much (and that time doesn't necessarily come right away).

I'm not sure how much hope there is for your plants, but I would replace the soil (or else transplant somewhere shady, removing the old salty soil when you do) and add potassium (and non-soft water). I would also mist the plants (without soft water). I would add phosphorus, too, but that's me.

Repotting may stress the plant further, though. I'd probably just transplant it at this point (and shade it), as that probably wouldn't be much different than repotting while hardening off. Don't transplant when it's sunny (I prefer to do it at sunset or when it's cloudy).

Whatever you do, don't water the garden with soft water. It may have some long-lasting consequences.