We've gone over properly lighting your plants, so it's only appropriate to also discuss another important resource for your plants' survival: water! Plants use water for a variety of functions, the most important one being photosynthesis. Combined with energy received from sunlight and carbon dioxide from the air, it is their process for creating food. Plants also use water to draw nutrients from the soil and to keep their stems and leaves firm through transpiration. Without adequate water, plants will lose strength and begin to droop and wilt. On the flip side, too much water can cause root rot. Since they're related, I'll also be touching on soil here and there throughout this guide as well.
How often should I water my plant?
Figure out your plant's native origin. Just like with most aspects of caring for any plant, knowing where it naturally grows in the wild helps you figure out how much of each resource it needs. Most plants that are commonly cultivated as house plants today fall into two categories: arid and tropical.
Arid plants are natively found in dry, hot, bright environments, like sparse deserts, rocky crags and sandy lowlands. Common plant examples are cacti and other succulents. Arid plants will generally require less water than most other plants. Only water them when their soil is completely dry.
Tropical plants, as their name suggests, are natively found in wet, humid rainforests and jungles. This includes almost all leafy foliage plants commonly found in homes today. Plants in this category have a slightly larger range in watering requirements, but most will fall under a) moderate or b) moist. a) Moderate: These plants, like pothos and philodendrons, will only want to be watered once the top inch or two of its soil is dry. Use a soil mix that contains ingredients that help the water drain through rather than retain it, such as perlite, orchid bark, etc. in order to help prevent root rot. b) Moist: Plants in this category include many ferns and prayer plants like calatheas, and they prefer their soil to be a bit wetter, but not soggy. What does this mean? For the most part, it actually just comes down to their soil type. Use a lightweight soil mixture containing ingredients that help balance how much water drains through (to prevent root rot) and how much it retains (to keep it moist). For example, perlite is light and good for drainage, and moss is light and good for moisture retention. Both ingredients help keep the soil light and fluffy. With just this difference in soil, water only once the top inch or two of its soil is dry, same as the moderate tropicals.
While not all house plants fall neatly into these two categories, they are the most common ones. If your plant is from a different place of origin, just consider what the climate is like in its natural environment and try to replicate it.
How do I know how dry/wet my plant is?
The simple answer is just to stick your finger through the top of the soil. Caring for any plant means having to get a little dirty from time to time. However, just using your finger can be a bit subjective and require some guesswork (ex. cold soil can make it feel wetter than it actually is). My number one advice for all plant parents is to use a moisture meter. These simple devices have one or two prongs that you stick into the soil, which allows them to read the moisture level. While every meter is different, each one will usually come with a chart of different kinds of plants and a number assigned to each type. The number will indicate when it should be watered. For example, my moisture meter has a 2 next to sansevieria, which means that I should not water my sansevieria until its soil is down to 2 on the moisture meter. Tips for using a moisture meter:
Be gentle when sticking the prongs into the soil, as you don't want to damage your plant's roots.
Since you're generally checking the top 2-inch layer of the soil, that is how far down the prongs will need to be. The bottom of the pot will usually be wetter than the top, so don't go too far down.
Leave the moisture meter in the soil for a few minutes. The meter will often start at a higher number before slowly lowering and settling down at its proper reading.
Check multiple parts of the soil. Different parts of the pot will often be wetter or drier than other parts of the same pot. I recommend checking in a triangle and going with the most general reading of the 3 points.
Always err on the dry side. Underwatering is much easier to fix than over-watering. I actually subtract one or two levels from my meter's chart. For example, even though the chart says I should water my sansevieria when its soil reaches 2 on the meter, I wait until it is at 0 before watering. *This is the best practice I've found with my own moisture meter. Yours may be different, so experiment cautiously.
Like all your tools, clean and disinfect your moisture meter thoroughly before using it on each plant. This helps prevent transfer of pests and disease between plants.
How much water should I give my plant?
Whenever it's time to water your plant, always thoroughly soak the entire pot. Every inch of the soil should be as wet as it can be, even for arid plants. More on this below.
Top-Watering vs. Bottom-Watering
The most common way to water house plants is by pouring water on top of the plant and letting it drain down through the soil and out the bottom, whether with a watering can, a hose, shower head, etc. When watering this way, it is important to make sure all of the soil is thoroughly soaked, because your plant's roots are closer to the bottom of the pot, not the top. Pour water evenly throughout the surface of the soil until it starts to drip out of the bottom, and then keep adding more just to be safe. I recommend doing this in a basin that allows you to save the excess water that drains out to be re-used again for another plant. Water conservation is serious business!
An additional advantage of top-watering for foliage plants is that any water that runs off of your plant's leaves, like rain, cleans them of dust and debris, which is great for keeping their ability to absorb light in tip top shape. It also has a chance of dislodging some pests that could be living on those leaves (though a more targeted approach, like wiping down each leaf, is still better for pest management).
The second way to water your plants is bottom up, which is also a great way to reduce waste, as well as to water multiple plants at the same time, but requires pots with drainage holes (more on this later). Fill up a container large enough for your pot to comfortably sit in, like a large basin or sink, with water. When your pot is sitting inside the container, there should be enough water to reach the bottom of the soil. Through the holes in your pot, the soil will draw water upwards via capillary action, only taking in the amount that it can hold and no more. Leave your pot in its water bath until water reaches the very top, which could take anywhere from 10 minutes to a couple hours depending on the size of the pot. Sometimes the top layer will never get wet, in which case you can simply top it off with water before removing your plant from the bath.
Bottom-watering is especially great for plants that do not like to have their leaves wet, like succulents and african violets. Keep in mind that really small, dry pots may be so lightweight that they will float in your water bath and topple over (this has happened to me with small succulents that need to dry out completely before watering), and very large pots will be extra heavy when soaked with water and may be difficult to lift. Bottom-watering is also how most self-watering pots work.
Use the proper pot/planter.
As a rule of thumb, use a pot that allows about an inch of space between your plant and the edge of the pot. Soil in small pots will dry out faster, and soil in large pots will retain more water. One of the best ways to prevent root rot is allowing excess water to drain out of your plant's pot. This most often means using a pot with drainage holes (with a saucer to catch the excess water if necessary). If your pot does not have one, there are two ways you can handle it:
Depending on the shape of your pot, you can usually drill your own hole at home quite easily with the right drill bits to prevent cracking or shattering. For unglazed clay pots, use a common masonry drill bit, and for glazed/finished ceramic pots, use a diamond-tipped drill bit (usually used for glass/tile). Drilling tips: a) For unglazed pots, soak the bottom overnight to help soften and prep the material for drilling. b) For safety, use protective glasses and a face mask and set up in a place with good ventilation, preferably outside, to avoid breathing in dust. c) Place your pot on flat stable surface, but add an old towel, a piece of cardboard or some other cushiony object in between to help prevent scratches on the lip of your pot. d) Use a rough tape like painter's or masking tape on the exact spot where you want the hole to provide traction for your drill bit and prevent it from slipping around until you make the first indentation. e) Go slow and steady, and add water to the hole as you work in order to keep the area lubricated.
If you can't or don't want to drill a hole in your pot, keep your plant in its plastic nursery pot (as long as it hasn't outgrown it) or in a pot that does have a drainage hole, and put that pot inside the pot you want it to be in. The outer pot essentially acts like a large saucer and catches any excess water that drains out of the inner pot. Just like any saucer, make sure to empty it of any standing water.
Unglazed vs Glazed vs Plastic Pots
The finish (or lack thereof) of your pot will give it different attributes. Unglazed pots, like common terra cotta pots, are porous, which means they will absorb excess water and dry out the soil a bit faster. They are great for plants that prefer drier soil and plant parents who tend to over-water. Additionally, their porosity also allows for air flow, which stimulates healthy root growth. On the flip side, glazed pots are not porous but keep more water in, which is a good choice for plants that want more evenly moist soil and plant parents who under-water, whether from forgetfulness or lack of time. Plastic pots are similar to glazed pots in that they lack porosity but retain moisture. They are also much more lightweight than all clay/ceramic pots, more flexible, durable and easier to clean.
Signs of Under- or Over-watering
While all plants have their own way of expressing different kinds of stress, in general under-watering usually shows up as drooping/wilting, browning, curling and crisping leaves. Some plants will droop dramatically when it's time to water, such as peace lilies and pothos, and will perk right up with no signs of trouble if they receive enough water in time. Brown, crispy leaves cannot be restored and will simply die off.
Again, signs of over-watering will vary between plants, but often shows up as drooping, yellow leaves (these also cannot be restored), and the stems will become mushy and limp from excess water. The worst of these signs will be root rot, which includes mushy, smelly roots. If this happens, remove as much of the dead roots as possible and either a) re-pot it in a smaller pot with well-draining soil if there are some roots remaining or b) place your plant in a tall container of water to try and re-root it if it no longer has any to sustain itself (change out the water daily).
Keep in mind that changes in color and texture of leaves can be signs of many different issues, including light, pests and disease, so use good judgment when trying to diagnose any plant problems.
Other Watering Notes
While some plant parents water all their plants at the same time, ideally every plant has its own unique schedule that optimizes its water intake. No matter how often you water your plants, be as consistent as possible. I use a spreadsheet to keep track of all my plants' schedules because I like spreadsheets, but you should find a way that works for you.
Plants' watering needs will fluctuate with the seasons, just like they have a growing season and a dormant season. During the warmer months, plants are consuming more resources to grow, and more sunlight and higher temperatures will cause water to dry faster. Therefore plants will need more water during these months. By contrast, plants are more dormant in the colder months, consuming less resources, and lower temperatures keep water drying out more slowly.
As one of the key resources to any plant's survival, it is important to understand your plant's watering needs. I hope this guide has been helpful in equipping you with the knowledge necessary to keep your plants thriving and loving life! For even more care tips, check out our guide to proper light for your plants!