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I just transplanted 6 cucumber plants from one of those Burpee seed starting crates to a large outdoor planter (sits on my roof deck). They were doing great indoors, but within a day or so of going outdoors, developed these white areas, and some of the leaves have wilted off. I'm using an automatic irrigation controller for watering, the planter is 9" of soil on top of ~3" of packing peanuts, with drainage. Full sun. Any ideas on what this could be?

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  • I have the EXACTLY the same issue with my pumpkins seedling. I have it in my greenhouse until 14 may (which is our normal no frost season ) and after a few days, i notice leave being bleached (part of the leaves). A few days later, the whole upper side of the stem being bleached and withered, but the bottom part of stem still ok. you can notice, ever part of the bleached surfaces are sun facing. it is may here in Germany, the weather is hot and cold and hot.. not stable.. hence, you think it is no more frost, but the sun can be sometime burning.. especially to seedling such these are proned to
    – andrew_ysk
    May 18, 2021 at 9:23

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Probably transition shock - your description of what you did does not include a period of hardening off for the plants, so if they were under shelter or inside originally, then planting them straight out without hardening off means they've responded to the cooler/colder conditions by producing whitened areas and a bit of die off. The only thing is, when I look at the photos, those whitened areas do rather look more like white fungus, but that might just be a trick of the light off the wet leaves. If the whitened areas are within the leaf, and do not have a fungal fuzz over them, its transition shock.

UPDATED EDIT: I came back on to make suggestions as to what you should do if it is transition shock, but you've confirmed it probably is. It'll be night time temperatures that are the issue - they may now have adjusted already, but otherwise, cover them with something (not something that will touch the leaves though) at dusk and remove it first thing in the morning for a week or so, or till overnight temperatures are good, then leave uncovered on a mild night.

I'm still a bit concerned about fungal growth though - that compost looks to be pretty wet too.

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  • yes, no hardening. i assumed that comparable temperatures here to what's in my house (60-> 85 range night to day) and an elevated planter meant they'd be ok. clearly I'm wrong.
    – kolosy
    May 13, 2014 at 16:42
  • re: your edit - it might be fungal, I'll check when I get back tonight. It's not compost, it's just soil. I need to dial down my auto-water-er.
    – kolosy
    May 13, 2014 at 18:50
  • You're taking a chance with garden soil... always safer to put veggie seedlings in proper potting compost.
    – Bamboo
    May 14, 2014 at 11:04
  • they're still in the burpee thing.
    – kolosy
    May 14, 2014 at 15:51
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They are sun burnt. Full sun is far too strong for seedlings that haven't been "hardened off" to handle it. You need to get these plants into a dappled shade situation, and then move them gradually over the next week or so back into full sun. If you don't, they could die.

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  • hot caps or other lightweight airy covers wil help in the transition, as the plants dont want to be re-transplanted.
    – J. Musser
    May 16, 2014 at 3:42

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