How To Keep Indoor Soil Moist (11 Ways)

When growing indoor plants (or any plants really), correct watering is key to keeping them alive and thriving. Most tropical houseplants prefer soil that stays consistently moist, is not waterlogged, and is not dried out. Maintaining this delicate balance can be tricky, especially if you forget to check the soil often. But there are a few tips you can implement to help retain moisture in the soil without overdoing it.

Keeping indoor soil moist starts with the right soil mix, amended with peat moss, coir, or vermiculite. Managing environmental conditions, such as humidity and drafts, also plays a role. Finally, regular watering, mulching, and using the right container can all combat dry soil.

When following these 11 tips, it’s important to remember that for most plants, too much moisture is not a good thing. Excess moisture should still drain away, keeping the soil damp but not soggy.

1. Follow a Regular Watering Routine

A regular watering routine is essential to the survival of your houseplants. This prevents the soil from drying out and staying dry for extended periods, which can lead to wilting, yellowing, and early plant death.

By incorporating watering into your daily or weekly routine, you are less likely to forget to water. I like to check the moisture levels in the soil every few days, only watering the plants that need it. This will change depending on environmental factors, the size of the pot, and how much moisture the plant prefers.

Soggy soil attracts mold and fungus that can quickly kill off the roots of your plant. That’s why it’s vital to check the moisture content in the soil before watering, rather than watering on a strict schedule.

There are two easy ways to check the levels of moisture in the soil, helping you decide on the perfect time to water:

Use Your Fingers or a Chopstick

Insert your finger or poke a chopstick 1-3 inches (2.5-7.6 cm) into the soil in the container. If some potting mix sticks to the chopstick or your finger when you take it out, it means the soil is moist and you don’t need to water it. If no potting mix sticks to it, water the soil. 

Moisture-loving houseplants need water as soon as the top 1-2 inches (2.5-5 cm) of the soil is dry. On the other hand, drought-tolerant plants can wait until the soil is dry 2-3 inches (5-7.6 cm) deep.

Use a Moisture Meter

A moisture meter is a handy tool that can help you check moisture levels somewhat accurately, depending on the tool you are using. Most tools display numbers on a scale of 1 to 10, with 1 being dry and 10 wet.

These tools don’t tell you exactly when to water, as the right time will depend on the plant you are growing. For example, a fern may need water again when the meter is at a 5, while aloes only need water when the meter is at a 2.

This general guideline will help you understand moisture meter readings to adapt them to your chosen plants:

  • 1-3: The soil is dry.
  • 4-6: The soil is moist.
  • 7-10: There are wet conditions or excess moisture.

If you consistently see readings in the 7-10 range, you may want to look at 10 Signs Your Potting Soil is Too Wet to avoid issues with waterlogging and root rot.

2. Create a Humid Environment

The humidity level inside most homes is lower than what most tropical houseplants, accustomed to rainforest conditions, need to thrive. In winter the problem is typically worse, also impacted by the use of air conditioners or heaters throughout the year.

When the air is humid, the moisture in the soil evaporates far slower, leaving the potting mix damp. Dry air will draw moisture away from the soil, causing it to dry out much quicker.

Increasing humidity doesn’t only help keep potting soil moist. It is also great for the health of your plants, replicating the conditions they are used to in their native habitats and improving growth.

There are several ways you can increase the humidity around your plants to improve conditions:

Use a Humidifier

Using a humidifier is the easiest way to raise indoor humidity levels, providing the conditions your plants need to thrive. Too much can also have negative effects on your plants and may make the room uncomfortable, so ensure you balance the needs of your plants with manageable humidity levels indoors.

Levels between 30 and 50% are comfortable for most houseplants and safe for humans and pets. For plants that need higher humidity, you can place them in a humid room like a frequently used bathroom or kitchen.

Group Plants Together

Grouping plants together raises the humidity slightly around the plants as 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. Ensure there is still enough airflow between the plants to prevent the spread of pests and diseases.

Place Pebble Trays Below the Planters

Pebble trays are an inexpensive way to improve humidity around your plants, although they are not as effective as some other solutions. However, as long as it is done right, there is no harm in trying it to see if it helps your plants.

Here’s how to get it right:

  1. Fill flat trays with pebbles and place the planters on top. 
  2. Pour water till the pebbles are almost covered. The bottom of the planter should not touch the water to ensure 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. Choose the Right Potting Soil

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, making them ideal for plants that prefer dry soil like succulents, but not suitable for most tropical houseplants.

Your chosen potting mix should drain well but still hold onto enough moisture to keep the roots happy. Most specialized houseplant potting mixes come with the ideal ratio, but you can also amend regular potting soil with things like coir and vermiculite to provide the perfect conditions for root growth.

4. Mulch the Soil

Mulching is one of the best ways to keep the soil moist, often used in garden beds to limit water usage. Mulch is not as common in indoor gardening, but it can help retain water for any moisture-loving plants like ferns.

Use organic mulches like straw, shredded bark, wood chips, or coconut coir. Compost is another option, although this is most commonly used outdoors in vegetable gardens. Keep in mind that this moist layer of mulch can attract bugs and promote soggy soil, so additional caution should be taken.

5. Keep the Planter Away From Windy Sites

Keep your indoor plants away from winds and cold drafts that quickly dry out the soil. These drafts are also damaging to the plants themselves, rapidly changing environmental conditions and leading to stress.

Make sure your houseplants are not kept in the path of any windy open windows or doors. You may also want to weather-proof your doors and windows so that the planters placed near them are not exposed to cold drafts seeping through.

Also, keep plants away from ceiling or stand fans. 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 houseplants need light to thrive, many can’t handle the intense direct sun. Unless you’re growing succulents or herbs and vegetables indoors, most traditional houseplants prefer a spot with bright indirect light throughout the day.

Direct sun not only damages the leaves but also causes the soil to dry out much quicker. If you don’t water often enough, this can quickly lead to wilting and the death of your plant.

Keep pots near bright windows but out of the path of the direct sun, especially in the height of summer when sunlight is more damaging.

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 times its volume in water. This sponge-like material is great for improving moisture retention in soil, often used as a soil amendment when sowing seeds. Adding it to your potting mix can keep indoor soil moist for longer periods.

Vermiculite is also often used to improve drainage in soil. However, vermiculite does not improve soil aeration as much as perlite does, so it’s better to use both (along with a few other soil amendments) to effectively balance drainage and water retention.

If you want to use vermiculite in your potting soil, ensure that the rest of the mix contains ingredients that increase the drainage of the growing medium.

8. Mix Organic Matter With the Soil

According to several studies, an increase in organic matter in soil translates to a greater increase in moisture retention. Although these are large-scale studies conducted in outdoor conditions, the same principle applies to indoor gardens too.

If you need to retain more moisture in the soil, mix aged compost, well-rotted manure, or leaf compost while preparing the potting mix. Besides helping the soil retain moisture, this will also improve soil health and provide nutrients to the plants. Make sure you don’t overdo it, as too much organic matter can lead to soggy soil and root rot.

9. Use a Plastic or Glazed Planter

When choosing containers for your indoor garden, you may consider style or design first. However, the materials of the pot can have a big impact on plant health too.

Plastic or glazed pots help keep the soil moist for long periods by containing moisture, as opposed to terracotta or fabric pots that wick moisture away. Plastic or glazed pots can be helpful for plants that prefer consistently moist soil but aren’t recommended for drought-tolerant plants.

If you don’t like the look of plastic containers, you can always use decorative covers to better suit your home. But as these usually don’t have drainage holes, make sure you remove the pots from these decorative covers before watering.

Alternatively, you can grow your plant in a porous planter as the main pot and place them in a slightly bigger decorative or cache pot. This will slow down the moisture-wicking ability of the porous planter because the cache pot will limit air circulation.

10. 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. It also keeps the leaves dry, preventing problems with disease, and limits the risks of over or underwatering. If you struggle to keep the soil moist, these kits are a great investment.

11. Use a Self-Watering Container

Self-watering pots use reservoirs that hold water and deliver moisture to the soil when it begins to dry out.

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

In another, an inner unglazed pot is placed 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 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. However, some can leave excess moisture in the soil, not suitable for plants that need to dry out a little before watering again.

Final Thoughts

Keeping indoor soil moist helps your plants thrive by providing a steady source of moisture at the root zone where it is needed. As long as you don’t overdo it, these tricks can help keep your plants happy and save water at the same time.

Dr. Moritz Picot

Dr. Moritz Picot is a horticulture enthusiast and the founder of TheGrowingLeaf.com, where he serves as the lead content writer. He established the website in 2022 as a valuable resource for both gardening aficionados and beginners, compiling all the gardening tips he has accumulated over the past 25 years. Alex has a passion for nurturing plants, transforming backyards into inviting spaces, and sharing his knowledge with the world.

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