The leaves of our plants tell a story: how long ago was it last repotted? Was it infested with pests? Did it sustain damage in transit? You can tell a lot about the history of a plant just by looking at the leaves. In this post, I’ll be discussing what to look for in the leaves of plants, and how to make sure you’re purchasing healthy plants by looking at the leaves.
The leaves of our plants are like solar panels: they allow the absorption of sunlight, which is transformed into energy. Plants use the energy they collect with their leaves to create new, larger leaves, which allows them in turn to collect even more energy, with which they create even bigger leaves. This is why when newer leaves are significantly smaller than the older leaves, it’s an indicator that something is wrong. Sometimes new leaves can be slightly smaller than their older counterparts because of normal changes in the environment. Perhaps it was getting colder when the leaf was developing, or maybe the plant was repotted then. This usually results in the developing leaf being smaller than preceding leaves. The newest leaf might also be smaller than older leaves because it is still growing.
However, if a leaf is significantly smaller than the rest, that suggests that the plant underwent some kind of major stressor during its development. It might be transport damage, a bad infestation of pests, or a drastic change in conditions.
If you find out roughly how quickly your plant grows by dividing the amount of leaves it has produced in your care by the number of months you’ve owned it, you’ll be able to tell how long ago it was repotted, or when it began to low down its growth for winter. Of course, this is a rough measure, but insightful nonetheless.
More often than not, leaf deformities are indicative of pests or disease. Leaves that will not unfurl, even when newer leaves are forming, are often the result of some kind of fungal infection. Meanwhile, leaves that are “lumpy” or wavy in shape when they should be smooth may be caused by thrip damage. Sometimes, when a repotting has been particularly rough when a leaf was still developing, it can take on an odd shape, and may be smaller than other leaves.
Because different plants are infected by different fungal infections, conduct research as it relates to your specific plant to find solutions.
Necrotic spots on plants indicate either bacterial infection or sunburn. Sunburn will cause brown, necrotic spots on your plants. Often, these will dry up after briefly turning mushy. You can generally tell when a plant has been sunburned because you left it in hot sunlight. The leaf will also generally feel warm to the touch if it was sunburned.
Bacterial infections cause necrotic spots that spread on leaves. Generally, these are to be left alone so the plant can do away with the bacterial infection with its immune system. Simply provide care as usual. That being said, some bacterial infections can be treated with streptomycin and/or oxytetracycline.
Advice for buying plants
When buying plants, choose plants which have healthy looking leaves. That is, there are no necrotic spots or deformities, and each successive leaf is larger than the last. Also look for new leaf growth. New growth generally suggests that the root system is intact.