Properly Watering Container Houseplants

Houseplants come in many different shapes and sizes, and their diversity continues to increase as the houseplant hobbyist community grows. While most plants can be grown inside and can be considered houseplants (for example, a lemon tree grown inside during winter months), houseplants are generally categorized as aroids (aglaonemas, philodendrons, pothos, ZZ plants, monsteras, etc.), succulents (snake plant, aloe, jade, euphorbia, etc.), ferns, begonias, orchids, bromeliads, and many more.

Due to the wide variety of houseplants, one of the biggest concerns for new houseplant owners is whether or not they can properly take care of their plants. Most often, poor houseplant growth and even death is due to improper watering. Fortunately, knowing the basic houseplant caretaking techniques for watering can help grow healthy indoor plants.

This Extension publication provides information on houseplant health and growth with regards to water management. It discusses potting soil properties, container types, watering methods and scheduling, growing conditions, and common symptoms of water- related stress.

Potting Soils and Drainage

Popular potting soils are often composed of organic materials like peat moss, pine bark, wood fiber, or coconut coir or inorganic materials like perlite (small white particles in potting soil formulations; see fig. 1). The ratio of these ingredients determines how much water and oxygen is available for the plant. For example, potting soils composed of mostly fine particles or fibrous structures like peat moss and coconut coir will often hold more water and less air, while potting soils composed of more coarse materials like bark or perlite will readily drain after watering.

Regardless of the type, most commercially available potting soils are engineered to drain well and contain plenty of air space during and immediately after watering. This potting soil composition reduces the chance that you will “drown” your plants by watering too much. Plants in containers should always be thoroughly watered, meaning the potting soil is wet all the way through. The container should be allowed to drain until water stops dripping out the bottom. If your container is in a drainage tray, do not keep it in water for more than 60 minutes. Overwatering is not about how much water you apply; it’s about how often you water.

In general, the majority of commercially available potting soil mixes will be adequate to grow most houseplants. It is only a small percentage of plants, like orchids and some succulents, that require more specialized soils.

While good drainage is a useful property, drainage should not be determined by how much water drains out of the pot after watering. It’s more important to gauge how much water is retained. Dry potting soils, especially peat or bark-based ones, can become “hydrophobic,” which means the potting soil repels water (like two magnets with the same charge). Excessive and quick drainage usually indicates that the potting soil did not hydrate sufficiently. You can identify if your potting soil is hydrophobic by lifting the container after watering. Does it feel light?

Another method to check for hydrophobic soils is to carefully place your hand flat over the potting soil surface, turn the pot upside down, and remove the container. Does it look wet in some areas and dry in others? You can also poke your finger into the potting soil to see if it is dry in the middle of the pot. In either of these cases, two or three slow applications of water will help hydrate dry potting soils.

Container Size and Types

There are several different container types commercially available at garden centers and retail outlets (fig. 2). The type and shape or size of the container can influence the rate at which potting soils will dry.

Container Height

The height of the container significantly influences how much drainage occurs. Specifically, taller containers will drain more than shorter containers. The upper few inches of potting soil will typically dry faster in a taller container. This is because taller containers have more gravity acting upon the moisture in the potting soil.

Shorter containers drain less after watering, which means the potting soil has more of its pores filled with water and contains less air space for root growth. Interestingly, the width of the container has no influence on drainage.

Container Volume

In small containers, the smaller volume of potting soil does not have the capacity to store water for long periods of time. Since water is also lost and absorbed by plant roots, potting soils tend to dry out faster in a smaller container than in a larger one (similar to how long it takes a small puddle to dry versus a deep puddle). Thus, a houseplant growing in a small container may require more frequent waterings.

On the other hand, large containers require a larger volume of potting soil and can usually store greater volumes of water than small containers. Thus, plants growing in large containers may need to be watered less frequently. Be careful not to transplant a houseplant into a container that is too large. This can result in roots growing in a rootzone that is too wet.

Plastic Containers

Plastic containers are one of the most popular types of containers because they are lightweight, durable, and cheap. These containers are nonporous, so they only lose water from the drainage holes and the surface of the potting soil. While most plastic containers come with drainage holes, some do not. This can create saturated and waterlogged conditions, which can lead to root rot or the plant drowning. If there are no drainage holes in the base of the container, you may need to drill some and create your own.

Clay Containers

There are two types of clay containers: porous and nonporous. Porous clay containers are often called terracotta pots. Terracotta is a type of clay that is fired at low heat and is unglazed, which means that moisture can evaporate through the walls of the pot. Regardless of the potting soil used, terracotta pots will tend to dry out the rootzone more quickly. Rapid drying can be a disadvantage to moisture-loving plants and an advantage for arid plants (cacti, succulents, etc.) and other houseplants that do not prefer high moisture.

Glazed clay pots are processed differently because they are fired at higher temperatures and have an external coating. Glazed clay pots are nonporous, meaning they do not lose moisture through their walls. Thus, potting soil in glazed clay pots holds water longer, which can be useful for plants that require more hydrated rootzones. Many glazed clay pots do not have drainage holes and are often intended for decorative use with plastic pots placed inside. Therefore, it may be necessary to remove the plastic pot when watering.

Orchid Pots

Orchid pots typically have large holes or slits in the container wall. This specialized feature allows the potting soil in these types of pots to dry out evenly and quickly mimic the natural growing conditions of plants like orchids, bromeliads, and some ferns.

Methods of Watering

Overhead Watering

Overhead watering is the most common method for watering houseplants. Overhead watering simply means that you deliver water to the rootzone from above the potting soil surface, and it infiltrates downward. When watering overhead, ensure that the water is being delivered on top of the potting soil by watering below the leaves.

It is important to note that not all houseplants prefer overhead watering. Some plants are intolerant of having wet foliage, which can make them susceptible to diseases, infections, or rotting. Some of these plants include African violets, begonias, cyclamens, and some cacti. Moreover, depending on your water source, mineral deposits like calcium can leave residues on the foliage.

Bottom Watering

Bottom watering is another popular method for irrigating houseplants. Bottom watering can be achieved by placing a shallow basin filled with 2-3 inches of water under the potted plants (see fig. 3). Plants should stay in the water for 15 to 30 minutes, depending on the soil dryness. The bottom-watering method can also be used to hydrate potting soil that has become hydrophobic, though hydrophobic soils may take longer to hydrate. Like a sponge or a paper towel slowly absorbs water when in contact with moisture, potting soils act the same way and will adsorb water upward.

There are two ways to confirm that your plant has received ample water from bottom watering. First, check the surface of the potting soil. If the surface is moist, then enough water has been adsorbed and provided for the plant. If the soil was hydrophobic, repeating the bottom- watering process may be necessary until the soil feels moist. Second, assess the physical appearance of the plant. If the plant was wilted but now has “perked up,” there is enough water in the rootzone. Container houseplants should not be left in basins of water for an extended period of time (more than 60 minutes), or root rot could occur.

The bottom-watering method is only possible if the container has drainage holes in the bottom. This method is often recommended for (1) plants that cannot tolerate wet leaves at all, like African violets, begonias, and cyclamens; (2) some cacti and succulents that are susceptible to leaf diseases; and (3) houseplants that have dense foliage, which can make it difficult to overhead water.

The bottom-watering method can also be used to apply diluted fertilizer solutions or fungicide or insecticide solutions. Since bottom watering is effective at hydrating the soil, applications with fertilizer or pesticide solutions should not occur too frequently and should be periodically rotated with regular water between watering schedules.

Self-Watering Containers

Specialized containers for house plants exist to aid plant owners with watering. These containers are built with a water-holding reservoir on the bottom of the container below the soil level. These reservoirs are filled with water, and a wick is used to draw the water from the reservoir up into the potting soil. These systems are designed to keep the potting soil evenly moist over time. They are effective for most houseplants but not for plants that prefer dryer soil. The reservoirs should be checked regularly to keep them full and cleaned periodically to prevent waterborne diseases or algae from growing in them. These containers may be more expensive, but self-watering containers work well for houseplant owners who travel or have limited time for maintenance but still want the experience of having healthy houseplants.

Misting vs. Watering

Misting can be beneficial for houseplants that prefer humid environments, but it needs to be done frequently. Misting entails spraying fine droplets of water on houseplant foliage. Misting does not replace the need for regular watering and is only a temporary solution to increase humidity. Most houseplants do not benefit from or tolerate misting.

Watering Schedule

How Much Water?

Understand your houseplant’s water needs. One of the most common houseplant care questions is, “How much should I water?” Regardless of the type of watering method used, enough water should be applied to thoroughly hydrate the total volume of the potting soil in the container. If applying water overhead, add several large applications of water to ensure the potting soil is adequately hydrated. Afterward, wait until water is no longer dripping from the drainage holes. If bottom watering, wait approximately 30 minutes or until all the water has been adsorbed upward. To verify that the rootzone was properly hydrated, gently turn the container upside down and remove the container, or stick your finger into the potting mix 1-3 inches (depending on the size of the container) to check for dry spots. If you find dry spots, slowly add more water until it stops draining and check again. Repeat until the entire rootzone is moist.

When To Water?

Each houseplant is unique and grows differently. Most houseplants do not need a rigid or regular watering schedule, but they do need frequent monitoring so you know when to water them. Plants like succulents and cacti rely on thorough but infrequent waterings, for example, once or twice a month. Tropical houseplants rely on more frequent waterings, sometimes once or twice a week because their natural environment is very moist.

Consistent monitoring of the potting soil’s moisture is key and can be done using the finger stick test or a soil hygrometer or water meter. As mentioned previously, self-watering containers can help with keeping the potting soil moisture at the appropriate level for longer periods of time.

Time of Day

The time of day is important when watering houseplants. Watering at any time of the day can hydrate the potting soil, but the plant will generally only absorb the water during daylight hours and when photosynthesis is occurring. Watering houseplants in the morning is best so there is adequate time for the potting soil to drain and for the plant to absorb the water throughout the day.

Time of Year

Plant growth is most active during the spring and summer months. Actively growing plants require more water, nutrients, and sunlight. Autumn is when plant growth slows down. Winter is when plant growth is the slowest, as some plants can go into dormancy with cooler temperatures and less sunlight. Monitor plants closely in the autumn and winter to avoid overwatering and limit root rot, disease, or death.

Indoor Conditions That Affect Plant Growth and Water Needs

Temperature

The average home temperature runs from 64 F to 75 F, depending on the time of year. Most houseplants can tolerate these temperature fluctuations; however, be aware of the following situations:

• A consistently warm temperature can lead to more active plant growth or cause the potting soil to dry out faster, which translates to more frequent watering.
• Extreme temperature fluctuations — like if the houseplant is in front of a sunny or southwest-facing window or near a heater where it gets hot for short periods of time — can cause the plant to use more water or dry out the potting soil faster when the container, potting soil, and roots heat up.
• Houseplants located next to a window in the winter may stay cooler and dormant, so they may need less water.

Humidity

Plants use water from the potting soil and lose water via a process called transpiration, which the process of water loss by evaporation from the leaf surface. Warm air and low humidity increase the rate of transpiration from a plant, whereas temperate air and high humidity decrease the rate of transpiration. Humidity levels in a home environment are naturally much lower than the humidity levels outside, especially when heat is running during the winter months. Most houseplants need more frequent watering and more water in the air when humidity levels are low.

Increasing humidity in the air can be accomplished by using a humidifier near the plants; using pebble trays with water under the plant containers, which adds moisture to the air through evaporation; and misting. Grouping plants closer together can help create a microclimate of moisture near their canopy and reduce transpiration.

In high humidity environments, houseplants need less frequent watering because the potting soil doesn’t dry out as quickly. Air circulation should also be improved to prevent diseases on foliage.

Light

Understand your houseplant’s light needs. Many houseplants prefer bright, indirect light. Higher light intensity can cause increased water use rates and growth, higher rootzone temperatures, and drier potting soil conditions — all of which mean more frequent watering. Plants that grow in lower light conditions need less frequent watering but may not grow as fast.

Type of Water Used

Tap water is the most common water source for houseplants and is generally suitable for most species because it is close to a pH of 7.0 (neutral) and doesn’t contain excessive amounts of elements and minerals.

However, some houseplants are sensitive to the chloramine disinfectant in tap water, so alternative water sources may need to be used. Distilled water is free of minerals and chemicals but is not appropriate for all houseplants because it lacks dissolved nutrients. Prolonged use may lead to nutrient deficiencies.

Carnivorous plants like Venus flytraps have delicate root systems and typically require distilled water for optimal growth because they obtain their nutrients from insects rather than fertilizer. Rain or spring water are options that have naturally occurring nutrients and minerals, but they are not in sufficient quantities to support long-term plant development.

Water from freshwater aquariums may also be used on houseplants, provided the tank is healthy and free from disease. Fish tank water contains nutrients (mainly extra nitrogen) derived from fish waste and uneaten food. Since this water can contribute to nutrient buildup in the potting soil, it should be used sparingly, and the potting mix should be monitored for salt accumulation.

Symptoms of Moisture Stress

Overwatered Symptoms

Plant roots need oxygen to grow and function properly. When the potting soil is wet for long periods of time, water fills the pore spaces, and oxygen availability will decrease. This causes roots to stop growing and eventually die, ultimately impacting the top growth of the plant.

Common symptoms of overwatering are (see fig. 4):

• Wilting of the plant foliage.
• Yellowing on both new and old foliage.
• Softening (mushy) of the leaves and stems.
• Leaves falling off the plant.
• Stunted growth.
• Rotten-smelling potting soil.
• Fungus gnats.

Solutions to overwatered symptoms include clearing any blocked drainage holes in the container, allowing the potting soil to dry out, repotting the plant into new potting soil, and pruning off dead or dying stems, foliage, or roots to stimulate new growth.

Underwatered Symptoms

Underwatered plant symptoms can often resemble the symptoms of overwatered plants. When the potting soil is dry and there is no moisture for the roots to absorb, a stress signal is sent to the leaves to stop transpiring. As a result, the first symptom of underwatered plants is also wilting of the foliage.

Underwatered plants commonly have the following symptoms (see fig. 4):

• Wilting of the plant foliage.
• Dry or brittle leaves.
• Brown tips or edges of the leaves.
• Leaves curl upward or downward.
• Leaves falling off the plant.
• Reduced or stunted plant growth.
• Dry potting soil has shrunk away from the edges of the container.
• Container and plant are very light in weight.

Solutions to underwatered symptoms include watering the potting soil and pruning off dead foliage to stimulate new growth. Bottom watering works best for this situation to fully rehydrate the potting soil. The saucer may need to be refilled several times with checks in between to make sure the potting soil becomes fully hydrated.

Summary

One of the main takeaways is that it’s better to underwater than overwater your houseplants. This implies paying attention to your watering frequency, not your watering volume. When watering houseplants, apply large volumes of water to thoroughly hydrate the potting soil and wait until the rootzone sufficiently dries before watering again.

Many factors can contribute toward how fast your houseplants will dry, some of which include the type of potting soil you use (coarser potting soils will need to be watered more frequently), the type of container (smaller containers, terracotta pots, and orchid pots will dry out more quickly), the time of year (you will need to water more often during the spring and summer months), and of course, the type of plant. Frequently monitoring the rootzone and leaf symptoms can help you better manage the health of your houseplants.

Additional Resources

Acknowledgements

The authors would like to thank Dr. Laurie Fox, Dr. Forrest Brown, Stephanie Romelczyk, and Michael Andruzyk for their time and effort spent reviewing this Extension publication. We believe their input has made a considerable contribution toward providing a clear and readable article.