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My tomato plants were doing great till a few days ago. Suddenly they started getting these white patches on the leaves, especially the leaves at the top and new leaves at the bottom. Some leaves, especially older ones towards the bottom started shrivelling and drying up completely and the plants will not support themselves any more.

They are on a window sill (I was about to start hardening them off) and I have had a few plants out of the pots to check for anything eating the roots and I didnt find anything. They have been potted on a few times already and after checking the roots I see they are not too big for the pots just yet.

From the white patches on the leaves I suspect a magnesium deficiency but some of the plants dont have the same problem. I cant find any evidence of any fungal or pest problems. I have been watering from the bottom a very small amount every day and the potting mix is just moist enough. Its a mix of around 60% coco coir, 30-35% compost and 5-10% perlite.

They are Minibell cherry tomatoes. They are in a window that gets the sun from 1 or 2pm till 8 or 9pm when we have sun. Its a bit up and down here at the moment in the UK. Any ideas? The white spots are more severe than the pictures show, it was hard to capture them in the pictures.

https://i.ibb.co/DDq718K/72-E537-B6-8-DF7-4967-9374-04-BD5-B0-DE932.jpg https://i.ibb.co/PhscgNz/394205-D2-D6-A6-4-EFB-B97-B-2-BA425-DB87-C4.jpg https://i.ibb.co/2KJ0DDP/4-AB9-F1-B0-9153-43-BC-925-B-BF7-ADA69-ECF7.jpg https://i.ibb.co/qpXRMkS/F4246-E8-C-B352-4-DD5-9879-1-A0-B092612-F8.jpg

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  • Watering once with 2g/L Epsom salt will cure any Mg deficiency. How big are these plants? Symptoms sound a lot like Fusarium wilt: en.wikipedia.org/wiki/Fusarium_wilt
    – Wayfaring Stranger
    May 23, 2019 at 15:47
  • Thanks. Ive had a look at that but it seems with this the wilting dries up the leaves. Mine are wilting but not at all drying out. Maybe they will so I will keep an eye on them and keep this in mind. Ive read to treat them daily for a week with epsom salts. Ive sprayed the once yesterday and once today and was planning on continuing till the week is up. Is it too much? The plants are around 40cm/16 inches.
    – waxxx
    May 23, 2019 at 16:58
  • waxx You should be alright, as long as you concentration is down near 2g/L. Mg+2 is not a usual fertilizer component because it reacts with phosphate to form a nearly insoluble sludge.
    – Wayfaring Stranger
    May 23, 2019 at 20:03
  • Do you mean I should be alright using it over the week or I should be alright giving them one dose? How long would it take to notice an improvement after applying the epsom salts? I cant see any difference so far but its only been two days. I'm using the concentration you recommend already.
    – waxxx
    May 23, 2019 at 20:19
  • Sprayed on over a week should work. I usually just make it up in water, and water the plants with it. If it's going to help, either way works.
    – Wayfaring Stranger
    May 23, 2019 at 20:27

2 Answers 2

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It honestly looks to me like it might be sunscald, or other damage from outdoors. It sounds like they haven't been outdoors, yet, though.

However, in addition to considering magnesium deficiency, zinc deficiency can make the leaves have white portions like that. If you're convinced it's not sunscald or wind damage, that would be my guess.

What I like to do to prevent obscure mineral deficiencies on plants (pre-transplant) is to add a little wood ash to the pots. It doesn't take much, and it acts fast. Just sprinkle a little on top of the soil and water it in. Now, of course, wood ash doesn't tend to have loads of each nutrient. It just has small amounts of most things—but the point is that it does have most of the nutrients in it that plants need to live, in proportions that were once used by a plant, even if most of those nutrients aren't had in great amounts (and a high percentage of the ash is water soluble, which is probably why you can see a difference in plants pretty quickly). I've personally found the amounts to be sufficient, whatever the case. I'm not talking about using it like fertilizer, although it does have some potassium and a little phosphorus in it (no nitrogen), but as a mineralizer for trace minerals. It has lots of calcium and carbon (so it may raise the pH if you use very much). If your potting mix is already too alkaline, adding wood ash may not be the best idea.

I've also used this zinc sulfate monohydrate, with good results. I put it in the soil. That was on outdoor plants (with zinc deficiency symptoms), though.

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  • They had not been outside when the pictures were taken. I'm 3 days in to hardening them off now and I have had to tie them to a garden cane to stop them completely falling over. It could be sun scald. I have all 6 minibell plants on one windowsill that gets the longest amount of sunlight (although not the strongest midday sun) and two of them in a window on the other side of the house. At first it looked like the 2 plants in the back window seemed to be showing similar symptoms, but as the days have gone by, the 6 plants from the front have got worse and the 2 from the back seem OK.
    – waxxx
    May 23, 2019 at 16:54
  • I will try the wood ash trick if I dont see any results with the espom salts. I haven't done a PH test but read about it a bit and I haven't been convinced of the best way. Most of the methods I can afford right now are these cheap digital prong testers that have pretty mixed reviews.
    – waxxx
    May 23, 2019 at 16:57
  • I see a heating vent on the floor. Are the plants getting too much warm, dry air?
    – Wayfaring Stranger
    May 23, 2019 at 20:04
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    Its a radiator. It was barely on before the problem and has been completely off ever since i noticed. It really must be something to do with the location but I cant think what. The sun hasn't been that intense and not much more intense than the other window. The radiator is off. The only other thing I can think of is they dont like something to do with the two gherkin plants close by. Otherwise I have no idea.
    – waxxx
    May 23, 2019 at 20:16
  • The window is open all day too so there is air circulation.
    – waxxx
    May 23, 2019 at 20:16
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Young plants in tiny pots being made ready to go outside?

I would not worry about them too much as tomato plants can take some abuse and survive and they are not in their prime growing location.

My advice would be to get them planted outside where they will remain and then see what happens.

My general approach to planting all tomatoes is to buy the largest starts I can find and plant them deeply. The plants will root out from the stem that is buried as it grows so that provides some extra root system to support the plant during the growing season.

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