Written by Jenelle Schafer
One of my college professors used to recite this statistic to us: "The #1 cause of houseplant death is underwatering. The #2 cause is overwatering." Many people I encounter that are self-proclaimed "plant-killers", generally fall into two categories. The first is the forgetful, neglectful gardener. They like the idea of being surrounded by houseplants, but when it comes to caring for the houseplants, they just can't remember when the last time was that they remembered to water their green (now turning brown) decorations. The second is the smothering plant lover. They simply love their plants too much. Unfortunately, their plants need some space to grow.
If you find yourself in either one of these categories, here are some rules of (green) thumbs to help you walk the line between the two statistics.
#1: Only water when the growing media is dry.
Before you decide that it is time to water your plants, check the growing media. A quick and easy check of soil moisture is to insert a finger into the growing media, down to the first knuckle. If the top inch of media is dry, then water. If it's moist, then don't water. If you can't quite tell whether it is dry enough, then wait a day or two before watering. Most houseplants, I have found, can be flexible when it comes to letting the potting soil dry out and because of the nature of most of their leaf tissues, a lot of plants won't immediately react to water stress.
The reason plants like the soil to dry out is because, as much as they need water to live and grow, they also need oxygen. Potting soil and other growing media are made up of particles. These particles, of varying shapes and sizes, when stacked around each other, have open spaces, normally filled with air. When you water properly, all the air in these spaces gets replaced with water. As plants take the water into their roots, and the media begins to dry out, air comes back into the spaces and roots again have access to oxygen, a necessary ingredient for respiration. When water sits in the pore spaces too long, and the roots are without oxygen for a long time, they get stressed. This leads to a condition we refer to as physiological drought. Even though the plant still has access to water, the roots are unable to take in any more water because they are under stress from a lack of oxygen.
Another reason it is good to make sure your plants are not sitting in wet media for a long amount of time is that moist environments are desirable for fungal diseases, particularly rots. Root rot and crown rot commonly occur because the growing media the plant is in has not properly dried out.
#2: Water frequency is more important than water quantity.
Underwatering and overwatering are results of timing. You can underwater a plant if the soil dries out too much between watering times. You can overwater a plant if you water too soon after the last watering and the soil hasn't had time to dry out. When you water, you should use enough water to saturate the media so that all the pore spaces get filled with water; excess water should be able to run out of the pot's drainage holes. After that, it doesn't matter how much more water you allow to run through and drain out of the potting soil, because the media will only hold onto the amount of water needed to saturate the soil. This is why it is really important to use a pot with drainage holes.
A good practice is to bring your plants to a sink when you are watering. Keep filling the pot with water until you can see it begin to run out the bottom. Let the excess water drain out and then it's good to go until the soil dries out again. If it isn't feasible to water in a sink, make sure you have the pot with drainage holes setting on a tray or inside another pot which can catch the draining water.
#3: Know the plant.
When you get to know your plants, and each of their unique growing characteristics and needs, it becomes easier to know exactly when to water your plants. Some plants use water quickly and don't like to be without access to it for very long. Other plants, like succulents, are alright going a little longer without water, but really despise having to sit in a spongy media. Individual research on each species will give you watering information, but also researching the wild growing environments of houseplant species should yield useful hints. Plants that grow in bogs naturally will likely be more tolerant of overwatering, and plants that grow in deserts will be more drought-tolerant.
Knowing what your plant looks like under normal conditions will also help you read your plant's needs. If a plant, like Aloe, normally has turgid leaves, but you notice they have become a little softer and flatter, then you should check the potting soil to see if it is time to water. If your plant with normally dark green leaves are looking a little more lime green, then check the growing media to see if it is drying out properly. Some people like to talk to their plants, but sometimes, the plants talk back.
Symptoms of Underwatering
Wilting leaves that eventually turn brown and are dry
Curling, shriveling leaves
Flowers and buds will drop
Symptoms of Overwatering
Wilting leaves that appear soft
Soft/mushy stems
Yellowing leaves
Brown roots
Problem-shooting
Sometimes, you can water one day and by the next, the media is dry again. While you can keep watering everyday when the media is dry, it may be better to look at repotting the plant to a larger pot. A larger pot can provide more space for water to be held in access to the roots. Another consideration while repotting should using a potting mix with a peat moss component. Peat moss is incredibly absorbent and retains water well in potting mixes.
If your potting soil just isn't drying out fast enough, within 7-10 days of the last watering, then you should evaluate the environment in which the plant is growing. Perhaps the pot is too large and you should change to a smaller one. Maybe the potting soil has too much peat moss in it and you could switch to a succulent mix which is more sandy and allows for better drainage. Moving the plant to a place with brighter light or more sun may encourage both evaporation from the media and the plant to use more water. Potting soil that is too old may become broken down and no longer effectively drains excess water, in which case it should be replaced with a fresh potting mix. Lastly, if there are different textures of media in the pot it can disrupt drainage. I personally, only use one type of media in a pot and don't use things like rocks, gravel or sand at the bottom on top of the drainage holes because water moves more efficiently through a consistent texture.
Conclusion
Hopefully these tips and explanations will help you establish a watering routine that both you and your plants will be happy with. I hate it when people tell me they can't keep things alive, because having a green thumb is not something you are born with, it's something you grow and cultivate through learning. By understanding one fact about plants ~that their roots need oxygen to be healthy~ you are already miles ahead into knowing how to water your houseplants. Happy watering!
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