How To Keep Indoor Soil Moist (12 Ways)


Houseplant parents often want to know how they can keep the planter soil moist for a long time. Some want to know because they don’t want their green babies to wither away while they are away on vacation. Others want to know because they are tired of lugging a watering can around the house and the porch daily.

You can keep indoor soil moist by mulching it, amending it using vermiculite or compost that holds on to moisture, or installing a drip irrigation system. Do not expose the plants to hot or cold drafts that suck moisture from the soil. Create a humid microclimate to prevent water from evaporating. 

There are several other ways to keep indoor soil moist. I will list and explain 12 such practices in this article. They are easy to implement and don’t require expensive or hard-to-find gardening supplies. 

1. Follow a Regular Watering Schedule

A regular watering or misting schedule prevents the soil from drying out and staying dry for extended periods. Depending on how quickly the soil dries out, you can set reminders to water every day or every 2-3 days. 

By incorporating watering into your daily or weekly routine, you are less likely to forget to water. 

The rule for watering indoor plants is to keep the soil evenly moist but not soggy. Soggy soil attracts mold and fungus. So, you must check the moisture content in the soil before watering. 

The following are two ways you can check the moisture content of indoor soil:

Use Your Fingers or a Chopstick

Insert your finger or poke a chopstick 1-4 inches into the soil in the container. If some potting mix sticks to the chopstick or your finger when you take it out, the soil is wet, and you don’t need to water your plant. If no potting mix sticks to it, water the soil. 

Use a Moisture Meter

A moisture meter is an inexpensive tool and gives accurate results. Most tools display numbers on a scale of 1 to 10. Here’s how to read the numbers on a moisture meter:

  • Reading Between 1-3: This indicates the soil is dry, and you should water the soil immediately. A reading between 1 and 2 means that the plant is also starting to dry out and may go into a shock if you don’t provide hydration.  
  • Reading Between 4-6: This indicates the soil is moist. You should water to bring the moisture level to a range of 4-6 when the reading shows 3 or less.
  • Reading Between 7-10: This reading indicates wet conditions, and you must not water the plant now. The soil in indoor planters tends to attract mold and fungus if the conditions are too wet.

If you wish to learn more about determining whether your soil is too moist, check out my other article: 10 Signs Your Potting Soil is Too Wet

2. Create a Humid Environment

The humidity level inside most homes is between 30% and 40%, which is lower than what most houseplants need to thrive. The humidity levels are lower in winter when the air is cold and dry. Sometimes, the humidity levels fall when you run the air conditioner or the heater. 

When the air is humid, the moisture in the soil does not evaporate, and the potting mix stays damp. On the other hand, dry air sucks water from the soil and dries out the potting mix.  

Here are four ways in which you can increase ambient humidity and keep the soil in the planter moist:

Use a Humidifier To Increase Humidity Levels

Using a humidifier is the easiest way to raise indoor humidity levels instantly. However, too much moisture in the air can make the indoors uncomfortable for the residents. High humidity levels can also lead to mold and fungal growth in the soil. 

The key is to strike a balance between achieving a humidity level that keeps the inhabitants of the building comfortable without drying out the soil in the planters. This balance can be challenging to achieve or maintain. 

Tweak the Settings on Your Heater or Air Conditioner 

You can adjust the heater, or the AC makes the room a little less hot or cold. Wear loose-fitting clothes made of natural fabric to keep cool instead of dialing up the AC. Or, layer up to remain warm instead of amping up the heater settings. These actions benefit the environment as well. 

However, adjusting the settings on your HVAC system may not always work. Also, you can change them only up to a certain level before living spaces become uncomfortable. 

Place the planters in naturally humid areas, such as kitchens or bathrooms that you use regularly. 

Group Plants Together

Grouping plants together creates a humid microclimate. The leaves, stems, and flowers of a plant transpire, releasing moisture into the air. 

When you keep several plants close to one another, the moisture released by each adds to and increases the humidity of the ambient air. 

You can place a can or a dish of water in the center to increase humidity.

Place Pebble Trays Below the Planters

Pebble trays are an excellent option to keep your indoor plants hydrated, and it is a relatively inexpensive solution. Simply follow these steps:

  1. Fill flat trays with pebbles and place the planters on top. 
  2. Pour water till the pebbles are almost covered. That is, the bottom of the planter should not touch the water. This space ensures the roots of the plant are not sitting in water.
  3. As the water in the tray evaporates, it increases humidity in the air around the plant.

3. Do Not Use Loose Potting Soil

Loose potting soil is great for germinating seeds and growing seedlings. 

Light and fluffy potting mixes let roots grow unhindered. Their porous structures allow excellent drainage that prevents the tender roots from drowning in water and developing root rot.

However, very loose potting mixes do not hold on to water. They tend to dry out quickly. 

Look for a potting mix that is somewhat dense but well-draining. You can also make your own potting mix by adding some clay balls. 

Now, as plant growers, you were probably warned about the disadvantages of growing plants in clayey soil

Clay soil is heavy. It is slow to drain and causes waterlogging and root rot. It also tends to compact, making it difficult for plant roots to grow.

However, clay balls are entirely different from the standard clay soil in your garden. 

Manufacturers create clay balls by baking and tumbling natural and pure clay at extremely high temperatures so that they become lightweight and porous. These balls expand in contact with water. 

You can add clay balls to your potting mix in three ways:

  • Add the clay balls to the bottom of the pot. Add about a 4 cm deep (1.5 inches approximately) layer of clay balls at the bottom of the pot. Then fill the pot with potting mix or compost. The clay balls retain water and, in turn, keep the soil in contact with it moist. 
  • Mix them into the soil. Mix clay balls into a loose, fluffy potting mix to make it more water-retentive.
  • Add them on top of the soil. Adding clay balls above the soil helps lock in moisture and keep the soil damp. 

Clay balls also go by the names: ‘clay pellets,’ ‘aqua clay balls,’ or ’hydro pebbles.’ Below are my top picks of clay balls for indoor gardening:

Organic Expanded Clay Pebbles Grow Media

These clay pebbles have a neutral pH, making them ideal for growing almost all plants. They are sterile, weed-free, and odorless. These balls have a striking reddish-brown color, and you can put them on top of the soil to make for a stunning display. 

These clay pebbles have multiple uses. You can use them to start seeds, anchor plants grown hydroponically, improve drainage in terrariums, and prevent temperature fluctuations around root zones in grow beds. 

Finally, and no less importantly, you will want to buy these clay pebbles from Amazon.com because a small business brand makes these balls. 

Onetour Hydroclay Premium Clay Pellets

These environment-friendly clay pellets improve aeration and let roots breathe. They retain moisture and then deliver the liquid and any nutrients you may add to the root zone of the plants.

The pebbles are oval and consistent in size, making them ideal for use on top of the soil. They are packaged and dispatched so that there are hardly any broken shards. You can buy these from Amazon.com.

Hydroton Original Fertilizers 

These expanded clay pebbles come densely packed in a 50-liter bag, so you get more for your money. These lightweight balls improve aeration and drainage while increasing the water-holding capacity of your potting mix. 

They are sterile, and you can use them liberally in your indoor planters without fear of introducing diseases and pests into your garden. The clay balls have a neutral pH, making them well suited to growing many plants and vegetables. 

They have an attractive red color and add to the beauty of any plant display if you place them above the soil. Best of all, they are reusable and save you money, especially if you are an avid gardener.

These clay pebbles are available on Amazon.com. 

4. Mulch the Soil

Mulching is one of the best ways to keep indoor soil moist. A layer of mulch several inches thick prevents moisture from escaping and keeps the soil hydrated. 

Additionally, mulch keeps the soil cool. Mulching will ensure the root zones of your plants remain cool on hot days. 

Use organic mulches like straw, shredded bark, wood chips, or coconut coir. 

You can also add a few inches of compost on top of the soil to act as mulch. This method is a great gardening ploy if you grow vegetables in planters. The compost will break down over time and add nutrients to the soil that will, in turn, feed your veggies. 

There are more ways to keep your planter-grown veggies well-fed and well-watered; read about these in my other article: How to Grow Vegetables in Planter Boxes

5. Keep the Planter Away From Windy Sites

Keep your indoor plants away from winds and cold drafts that quickly dry out the soil. Do not keep the planters in hallways and corridors that are often drafty. 

Weather-proof your doors and windows so that the planters placed near them are not exposed to cold drafts seeping through cracks and leaks.

Also, do not place plants directly under a ceiling fan or near a pedestal fan. The gusts of wind from a fan rotating at high speeds will dry out the soil. 

6. Keep the Planter Away From Direct Sunlight

Although most houseplants and vegetables grown indoors need light to thrive, you must shield the planter from the glare of the direct sun during the hottest part of the day to keep the soil moist. 

Here are a few tips:

  • Move the planters a few feet away from the window during the hot summer.
  • Use heavy curtains to shield the plants from the sun’s harsh rays.
  • Avoid placing planters near south and west-facing windows during summer months.

Being exposed to hot winds can also dehydrate indoor soil. Do not keep indoor plants near furnaces and radiators. 

7. Add Vermiculite to the Potting Mix

Vermiculite can absorb up to 3-4 more times its volume in water. It is a sponge-like material that retains moisture and stays damp for a long time. Adding it to the potting mix can keep indoor soil moist for extended periods. 

However, vermiculite is not as porous as perlite; plant enthusiasts often use perlite to improve the water-retention capacity of a potting mix. So, vermiculite does not improve soil aeration as much as perlite does. 

If you want to use vermiculite in your potting soil, ensure that the rest of the mix contains ingredients that increase the porosity of the growing medium. For instance, if you use vermiculite, you might also consider adding a fistful to perlite to improve soil aeration.

8. Mix Organic Matter With the Soil

According to the findings of this study, for every one percent increase in organic matter, the soil can hold an additional 16,500 gallons (75,010 liters) of water per acre. This water is readily available to plants. 

According to another study, a three-inch (7.62 cm) layer of leaf mold worked into the soil up to a depth of six inches (15.24 cm) increases its water-holding capacity by 2.5 times. 

Mix aged compost, well-rotted manure, or leaf compost while preparing the potting mix. Besides helping the soil retain moisture, compost will also feed your plants. 

9. Add Peat Moss on Top of the Soil

Adding a layer of peat moss on top of the soil helps lock in moisture and creates a warm and humid micro-environment that keeps the soil moist. 

However, there is an environmental downside to using peat moss for gardening.

Did you know that peat moss in bogs and wetlands stores a  third of the world’s soil carbon? These ecosystems are known as “carbon sinks” because they absorb and store a large amount of carbon dioxide.  

The process of harvesting peat moss releases carbon dioxide into the air. Unfortunately, peat moss takes thousands and thousands of years to form. So, the more peat moss people harvest, the greater the amount of carbon dioxide in the atmosphere.

So ensure you opt for products like the Hoffmans Canadian Sphagnum Peat Moss (available on Amazon.com)—a more sustainably sourced organic peat moss that won’t endanger our delicate ecosystem. 

10. Use a Plastic or Glazed Planter

Plastic or a glazed cement pot helps keep the soil moist for long periods by preventing water from wicking. 

On the other hand, terracotta pots or unglazed cement planters have a porous texture that absorbs water and lets it wick out of the potting mix. This porosity dries out the soil. If you use these pots, ensure that you check the soil daily and water when needed. 

11. Use Drip Irrigation

Installing a drip irrigation kit for your planters lets you moisten indoor soil without wasting water. These kits are easy to install and can be adjusted to provide water at a steady, gentle drip. 

Drip irrigation prevents water runoff while ensuring the soil and the plant’s root zones remain moist.

A drip irrigation kit is not just for those times when you go on a holiday and can’t water for several days. A drip system prevents mold and fungus buildup on leaves by keeping them dry.

If you seek more detail on drip irrigation, please read my other article: Drip Irrigation Vs. Hand Watering: Which is Better?

12. Use a Self-Watering Container

A self-watering pot consists of a reservoir that holds water. There are two designs of self-watering containers as follows:

One potting container uses a string thread that runs from the water tank to the potting mix and back to the tank. The string remains moist in contact with the water in the reservoir and, in turn, moistens the potting mix. 

In the other self-watering container, you place an inner unglazed pot inside a larger outer glazed pot. The outer pot functions to retain water.

The inner unglazed pot has a porous structure that absorbs water through its sides. The potting soil takes in the water and keeps the plant hydrated.

A self-watering pot provides a constant supply of water to the potting mix. The water is released slowly into the potting mix, so the soil does not remain soggy. 

A self-watering pot is also a great way to keep your indoor plants hydrated when you are not home for several days and can’t stick to a daily watering schedule.

Conclusion

Keeping indoor soil moist helps your plants thrive by providing a steady source of moisture at the root zone. It also benefits the environment. Every gallon of water you save daily adds up in the long run and brings down your utility bill. To recap, the best ways to keep your soil moist include:

  • Water regularly and monitor your soil moisture levels
  • Place your planters from wind and too much sun
  • Add mulch and vermiculite
  • Use peat moss
  • Change your plant container to non-porous materials
  • Use drip irrigation or self-watering containers.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

Recent Posts