This subject might be a little late in the season, but we haven’t yet covered “what sunburn looks like” when you are hardening off. Also, how much is too much.
This is a pretty severe case of sunburn, seen on our nasturtium. You can see the white spots, where some of the smaller leaves are also rather dried up and curled. This might deeply concern a newer grower, but for us, we’ve grown so many nasturtium that we’d darn near declare this as normal. Also, these spots aren’t increasing as we’ve increased the hardening off time, meaning it’s not getting worse.
What’s really important to look at is new growth and whether you’re seeing issues across the entire plant or just part of it. If sunburn affects the entire plant, that will be what truly “takes out” the plant. First leaves and even the first true leaves, in our opinion, can be somewhat “sacrificial” in nature. We don’t really care about them as the plant will typically put on many more.
In this case, our new nasturtium growth is coming in healthy, and we still have many healthy looking leaves. So, we know we can skate past this damage without having to severely slow down our hardening off.
Of all the plants we grow, we’ve found nasturtium and squash to be some of the most sensitive to hardening off. We’ve tried to slow it down, spending several days at 30/60 minutes, and often this isn’t even enough. In a few weeks time, there will near zero evidence of this sunburn, like it never happened. Same with squash.
With gardening, there’s always “exceptions to the exceptions”…but don’t let these technicalities scare you off. It’s always a learning curve, with a near infinite number of things to learn. That’s why we love to grow, it’s a life long learning process and you will never “have it all figured out!”