Let's be real, the leaves are the reason that we purchased the majority of our houseplants to begin with. Foliage plants are absolutely stunning. From the graceful variegation of a prayer plant to the deep velvety leaves of a philodendron micans, foliage is attention-grabbing. Aesthetics aside, there are a few basic traits to look at in the leaves of each one of your plants that can inform your care of them.
How Thick Are The Leaves?
A good general rule is that leaf thickness directly corresponds to the watering and humidity needs of a plant. A plant with thick leaves (think succulents, peperomias) is full of water, meaning it has stores to draw on before it will need to be watered again. Those leaves are also less likely to be susceptible to crunchiness and browning due to low humidity. That's a plant that has low watering needs, and low humidity needs - they'll be fine almost anywhere as long as they get enough light. They will signal that they need water by becoming slightly wrinkled, or less firm than usual. Gently bending the leaf in half and judging how easily it bends, or "the taco test", can be a great way to judge if your plant needs water.
A plant with more mid-thickness leaves (pothos, monstera, rubber trees, spider plants, fittonias) will probably have moderate watering needs, and moderate humidity needs. These plants again will grow just about anywhere happily as long as they get enough light.
You may see a few crispy edges here and there, but these plants are growable for pretty much everyone
Thin-leaved plants (palms, calatheas) seem to give people trouble. They tend to have higher watering needs, and very high humidity needs. A thin, delicate leaf doesn't store much moisture and will crisp up easily.
If you live in a particularly humid climate this may not be an issue for you, but for anyone not they can be difficult. A humidifier is going to be your best friend if you want these plants out in your home. If you don't have a humidifier, clustering several plants together can also create a small bubble of elevated humidity. Alternatively, placing the plant under a cloche, in a terrarium, or even under a clear sandwich bag that is kept closed around the stem can help to provide more humidity for the plant. Many people say that misting will help with this, I personally disagree, and have another blog post written on that topic in more depth, if you're interested.
Variegation
Whether or not a leaf has any variegation, and the degree of variegation can also tell you quite a bit about what your plant needs. Most of the time highly variegated plants need a lot of light to continue producing that degree of variegation, and it will fade slowly in lower light conditions.
One example of this is this red prayer plant, you can see the one leaf has reverted to green. That leaf was made when the plant was getting far less light than it is now. When the plant is getting insufficient light new leaves are made with more green because the green part of the leaf contains chlorophyll.
Chlorophyll is what gives leaves their green colouring. More chlorophyll means that the plant will be better able to photosynthesize. This is also why those beautiful pure white leaves on monstera albos never last long. They do not contribute to the plant and in fact, can be a burden. They require the plant to give them a constant supply of resources to support them but aren't able to contribute anything in return because of the lack of chlorophyll.
Another great example of this would be the polka dot plant. These pretty little freckled plants need a great deal of light to sustain their variegation. When they aren't given enough sun, they quickly lose their colouring and become leggy as they reach for more light. Luckily, they rebound quickly when returned to full sun and are pruned.
These are not hard and fast rules, nature has very few absolutes. However, they can be used as a helpful tool to begin to broaden your understanding of your houseplants. What observations from nature have helped you to better understand your plants?