Let’s discuss one of the primary dangers that comes from hardening off! Just like with humans, plants can experience a “sun burn” and if it becomes too severe, it can be lethal to the plant!
The telltale sign of sun burn is that the plant’s leaves turn white or creamy colored. It usually starts at the leaf’s edges, but can sometimes overtake an entire leaf. When allowed to progress to a severe state, the plant can lose the ability to photosynthesize.
It’s important not to misdiagnose this symptom as a nutritional issue. The “cure” in this case is to simply slow down hardening off a little bit. We usually recommend repeating about half the amount of time, for at least one or two days.
With our aggressive hardening off schedule, we do sometimes see a tiny bit of sunburn on some plants. Like with humans, a small sun burn is no big deal. But, a severe one is not an experience you want. We don’t get concerned with tiny sun burns, like you see here.
We look at a plant’s early growth, like first and second true leaves, as somewhat “sacrificial.” Our transplants will become many magnitudes larger over the coming months, a small sunburn on first or second leaves is practically inconsequential in the long run.
We find the plants most prone to sun burn are those with broad leaf structures. Examples are squash, cucumber and anything with large, flat leaves. However, we also find with most of these plants, new growth is fast enough that a little bit of sun burn is no biggie.
