Light levels inside greenhouses in winter and spring can often be quite low. Mostly because the glass has become dirty. With a ton of plants in my greenhouse it is difficult to reach the 12 ft (3.7M) rooftop glass.to clean it. The sides can easily be cleaned from outside, but inside it is often difficult to reach around large potted plants. The plants don’t seem to mind the lower light levels as long as they are warm and cozy. It is when spring rolls around that the difference in light levels becomes quite noticeable.
In an ideal world, plants should be moved outside for a few hours and then put back inside to gradually acclimate them to more intense sunlight. Because I have so many plants crammed into the greenhouse (over 200 at last count!), it takes a few days to move them all out and in fall, back into the greenhouse. This makes incredibly time consuming to expose them gradually to increasing light levels and it rarely gets done well.
The most obvious problem I notice when moving plants out of the greenhouse is leaf burn. For most plants that is not a big problem, but plants with very dark green leaves often suffer the most. The very worst problems are most often with Phalaenopsis orchids and clivia. Both have thick straplike dark green leaves, and both get sunburn when moved directly into sunlight after being indoors or in the greenhouse.
I usually put all the orchids and clivia in the shade of two large trees on the patio, but a very rainy spring ensured the trees weren’t fully leafed out when I set the plants out during a heavy shower. The rain was fine, but forgetting to cover the plants with shade cloth was unforgivable and both species got sunburned. Once the leaves are burned, they are usually dead. All you can do is hope you haven’t killed the plant and that it will recover quickly.
I put the Phalaenopsis back in shade and fertilized them religiously as if to atone for my sin. It took a year for new leaves to grow, but now the plants seem to be quite healthy again and are sending up flower spikes.
The clivia plants suffered more damage and I wonder if they will ever recover. They are now in heavy shade, but many of the leaves were severely burned, were removed to help the plant recover. The new leaves, if and when they come in, will be able to take stronger sunlight (I hope!) and should survive outside for the summer months.
The new leaves for both plants are lighter than the older leaves, indicating that the plant may be getting too much sunlight so I shall probably move the clivia back indoors before the sun gets too bright and burns the leaves over again.