Houseplant Harmony: Water + Light
Are you new to houseplants, or prone to killing them? This article is for you! We’re going to talk about two critical elements for keeping your houseplant happy: water and light.
Every houseplant species is different and home conditions vary, so there is no single prescription for how to care for every plant. We’re hoping to demystify plant care so that you can wield that watering can with confidence.
You Don’t Need To Water Every Day
More like once a week, or in some cases, once a month. In general, we advise giving your plants “a good drink,” i.e., thoroughly moistening the soil through the root zone (down where the roots are ready to soak up water), and letting it partially or completely dry out before watering again. Exactly how much and how frequently you water depends on the plant species and where you put it.
Here’s a refresher on photosynthesis, the process by which plants convert light energy into food for their own growth. While you don’t need to know photosynthesis in detail, understanding it at a high level is very helpful for intuiting good plant care choices.
Photosynthesis is: carbon dioxide + water + light energy → glucose + oxygen
The most important thing to note about this equation is the relationship between light and water. A plant that is receiving lots of light energy needs more water to photosynthesize, compared with a plant that is receiving less light energy. As we discuss below, not every plant requires direct sunlight, but there is a range of light intensity that work for any given plant, and where it is in that range will affect your watering. In other words, if your plant is in low light (more on what “low light” means in a moment), you should expect to water it less frequently than a similar plant in a bright room.
This also means that plants usually need more water in the spring and summer, when there is more daylight and stronger sun, than in fall and winter.
Fun side note about photosynthesis: it occurs in cells called chloroplasts, which contains the chlorophyll that give plants their green color. Generally speaking, the greener a plant is, the more light it can extract from its environment. So for example if you have a variegated white-and-green leafed plant, the plant will develop more white in its leaves if you put it in a bright spot, or it will develop more green in its leaves (revert) if you put it in a lower light spot.
Not All Plants Need (Or Even Want) Direct Sun
When we ask customers what type of light they have in order to point them to suitable plant options, many will look at us apologetically and say “it’s a bright room, but there’s no direct sun.” Rather than being banished from the store (“No direct sunlight, get OUT!”), they discover that there is actually a huge range of plants that survive in and even prefer indirect light environments. Think of plants that grow in the understory of a tropical forest—these plants are adapted to shaded environments, and for that reason they often do well indoors.
Every plant species is a little different, but most fall into a few major types or categories with regards to light and water. At Niche, our plant labels use the following scale:
Bright light — This means direct sun (most commonly you’ll see this for desert plants such as succulents or cacti).
Bright indirect light — What we mean by this is a naturally bright room but it doesn’t need direct sunlight; a spot with some direct sun is usually fine.
Bright/medium indirect light — A bright to average indirect light environment, or an office with fluorescent lighting (plants in this category tend to be the hardiest houseplants).
There are certain plants that can adapt to fairly low light conditions. For these we add a note: “Low light OK” — this means that the plant tolerates low light conditions, which is different from “thrives in.” What do we mean by low light? If it’s a space where you’d need to turn on the light to read something in the middle of the day, it’s probably what we would call a low light space.
Allow soil to dry between watering — This means exactly what it says: allow the soil to dry out completely between watering; it’s a fail-safe way to avoid root rot, which occurs when roots are sitting wet for too long (especially important for plants in low light).
Tolerates dry soil — This means that this plant species naturally holds a lot of water and therefore can hang out in dry soil most of the time, but it will need some “rain” to replenish its system occasionally (say every 2-4 weeks, depending on the plant, its size, and light conditions).
Prefers slightly moist soil — If you’re a beginner, this is often the trickiest category to master: you’re going for an even dampness in the soil, but never water-logging, as even plants that like moist soil are prone to root rot; you’ll want to add some water to the pot once the top inch or two of soil has dried out.
How Much Water?
This is actually a very difficult question to give a straight answer to, because it really depends on plant size, how extensive the root system is, how dry the soil is, etc. In most cases, you’re aiming to add enough water to the plant to thoroughly moisten the soil and entire root column without creating a swamp. A tiny plant might require just an ounce of water, whereas a floor plant might take a half gallon or more. Knowing how much to water is something that gets easier with time, as you get used to your plant and it gets used to you (and your house).
Sticking your finger in the soil is a great way to tell if it is truly dry or not. Visual cues are helpful but not perfect because a plant struggling with overwatering may not exhibit signs of stress immediately. If you think you’ve overwatered a plant, place it in brighter light until it has processed the water. If you think you REALLY overwatered, simply hold your hand over the plant and soil, and gently tip the pot until excess water runs out.