Water sometimes pools up at the surface of the soil when we water our potted plants. Although not very common, this is a problem that can easily be remedied by knowing the soil composition and how surface tension works.
Water will sit and pool on top of soil because the surface tension of the soil is greater than that of the water that is being applied to it. Other causal factors include soil composition, compaction, dryness, and drainage ability.
The difference in bonding forces causes the water to pool up at the surface for some time before it is fully absorbed into the soil.
The causal factors leading to water pooling up at the surface of potting soil are discussed further in this article which we reveal immediate and long-term solutions.
Reasons Why Water Sits on Top of Soil when Watered
- High soil surface tension
- The soil contains peat moss
- Soil allowed to get too dry
- Bad drainage – Water is suspended within the soil
- Soil type – Too much clay in the mix
- The Soil is severely compacted
- The Soil Lacks Amendments
1. High Soil Surface Tension
The surface tension of the soil plays a major role in how well water is absorbed into it.
Surface tension is increased when the soil particles are drawn close together as a result of dehydration.
With increased surface tension in soil, when it is watered the water will just linger on top the soil rather than soaking and moving downwards into it.
When this happens it means that the surface tension of the soil is greater than the tension between the water molecules preventing the water droplets to penetrate into it.
As a result, the water just sits on top of the soil.
Fortunately, this does not go on forever. The water will eventually soak slowly into the soil.
From a study posted by Forest Service – U.S. Department of Agriculture
It was found that –
The affinity or repellency of a surface for water originates from the attractive forces between water and solid surfaces.
If the attraction between water and a solid surface, such as that of a soil particle, is greater than the attraction between individual water molecules, then water will spread out and be adsorbed on the solid surface
2. The soil contains peat moss
Peat Moss is used in potting mix because of its ability to hold water, its lightweight and does not decompose as fast.
Peat substrate, however, when it is dry, will tend to repel water rather than absorb it, as it is known for.
For this reason, peat is one of the culprits that causes water to sit on top of soil if the plant was not watered for some time.
3. Soil allowed to get too dry
As mentioned before, when the soil is allowed to dry for some time the surface tension increases, preventing water from being absorbed.
Whenever potted plants are exposed to certain environments the soil can dry out pretty quickly.
Such conditions are –
- Too much sunlight –
The plant is subjected to too much direct sunlight which heats up the surface of the soil and dries up the moisture in that region.
- High air flow –
Whenever the wind is high the evaporation rate will increase causing the surface of the soil to dry out quickly.
- High Humidity –
As the humidity of the air around the potted plant increases so does the rate of evaporation.
This directly affects the soil as water is evaporated from it, causing it to become dry.
To take the guesswork out of determining how much moisture your soil has, you can use this cost-effective soil moisture meter from amazon.
4. Bad Drainage
Bad drainage will lead to waterlogging as water becomes suspended within the soil and is not allowed to drain freely.
As a result, when the soil is watered the water will just sit on the surface and not be absorbed into the soil as the soil is already saturated with water.
The effects of waterlogged soil are –
- Root rot
- Lower Oxygen levels for the plant in the root zone as the water takes up the air space
- Waterlogging increases the reduction potential of the soil reducing the absorption of nutrients from the soil
- Lowered nitrogen uptake through the roots
- It can damage the root tips and prevent absorption of nutrients.
Water logging can be caused by –
- Improper drainage
- Soil has too much clay
- Lack of proper soil amendments incorporated in the soil.
5. The Soil Type
The soil may be high in clay and low in organic material.
As we know clay soils have very low drainage ability as the particles are very close together.
When this type of soil is watered, a small amount of water will be absorbed before the rest starts pooling up at the surface.
6. Soil Is Severely Compacted
When the soil is compacted the spaces between the pores become very small.
Water absorption is greatly impacted and when the soil is watered it only takes a little water to completely fill the available spaces causing the rest to well up and sit on top of the soil.
With so little water being absorbed, the soil will tend to dry out quickly which can also increase the soil surface tension.
7. Soil Lacks Amendments
When the soil in a potted plant lacks amendments the soil can become severely compacted as described in the previous point.
Soil amendments helps increase drainage and aeration within the soil by creating air spaces and allowing water to drain through while still holding some degree of moisture within the soil
We go further into how much soil amendments to use further in this article.
(go to soil amendments)
If you would like an in-depth description of how these amendments work you can also see our article on soil amendments here.
I use this cost-effective soil amendment when repotting which enhances the soil and gives my plants the best growing conditions.
How to Promote Water Absorption in Soil
There are ways to help the water to be absorbed into the soil and this can be done by breaking the barrier that’s holding the water out.
There are three ways this can be done –
1. Creating pores for water to drain
Water can be allowed to seep into the soil if we create an initial path for the water to go.
This can be done by using a chopstick or some other thin stick and poking holes in multiple places through the top layer of dirt so that the water can drain into the soil.
However, this will not stop the topsoil from becoming hard again. A regular watering schedule will prevent soils from drying out and creating such hydrophobic barriers.
2. Removal and replacement of the topsoil
An easy fix to help water to be absorbed into the soil is to remove the problem.
The problem exists in the top layer of the soil where the soil particles are so close together that they create a bond that is greater than the forces holding the water particle together.
This layer is called hydrophobic soil.
Hydrophobic soils tend to have a high surface tension which can cause water to pool up at the top of the plant pot
Removing the top layer of the soil and replacing it with fresh potting mix or even compost can have multiple benefits.
Apart from just eliminating the problem, you will be adding fresh nutrient-rich topsoil to the pots which the plant will thank you for in the long run.
3. Use soil surfactants
Surfactants reduce the surface tension of water, allowing it to penetrate and wet soils more easily and evenly.
Soil surfactants or wetting agents are not a long-term solution and will have to be reapplied.
Surfactants can also cause damage to the microorganisms within the soil which will remove all the beneficial attributes of having them in soil.
How to Drain the Soil?
So you have poured water into the soil and have found that it just pools up at the surface with some lighter, buoyant soil floating around.
It can get annoying waiting around for the water to finally break the surface and start penetrating into the soil.
If this is the problem you can just tilt the plant so that the excess water can be drained out into a collection pan.
Now you may be wondering how then will you water the plant?
An easy, temporary alternative is to use the bottom watering technique which we discuss later on in this article.
Go to Bottom watering!
Although bottom watering is a very popular way to water plants, it should not be used as a permanent solution to soils with high surface tension.
How to Improve Drainage in Potted Plants
Inspect the soil and Change the Mix
The soil which is currently in the plant pot may have a higher ratio of clay within the mix which may be the reason why the water is not being absorbed into the soil.
Clay particles exist closer together and when watered it can cause water stagnation which leads to waterlogging.
If water is sitting on top of the soil and refuses to be absorbed. You may have hydrophobic soil as previously discussed.
Drill Drainage Holes in your Container
Drainage holes are a must in any plant pot. It provides a way for excess water to drain out of the pot.
If drainage holes are not present the water will end up pooling up within the soil causing it to become waterlogged.
Additionally, this may lead to problems such as root rot which will harm the plant and even cause it to die.
The average amount of drainage hole in any given plant pot is 4 which ranges between inch to inch in diameter.
Larger holes may also cause soil to leave the plant pot with the water and additional prevention methods will be required such as a filter material to keep the soil in place while water is draining out
Manually Aerate the Soil – Using a chopstick
Manually aerating the soil means fluffing the soil somewhat to help prevent soil compaction. When the soil is aerated it increases the availability of oxygen to the roots of the plant where it is needed.
It also helps with soil drainage ability providing spaces in between the soil particles for water to be absorbed and also drain out of the plant pot
There may be a concern that some roots will get damaged in the process but this will not kill the plant as if the soil remains compacted which will eventually suffocate the entire root system.
Add soil amendments
To make your potting soil drain better you should incorporate soil amendments into the mix.
Soil amendments may include substrates like perlite and vermiculite. They both work well when it comes to soil aeration and drainage.
Add a 1:1 ratio of perlite to vermiculite which would account for 30% total volume of the soil amendment mixture to create a well-rounded mix for drainage and aeration.
This is a sure way to rejuvenate, increase drainage ability and add extra nutrients to potting soil that has been in use or just sitting for some time.
You can find a cost-effective mix of perlite and vermiculite for all your potting needs on Amazon. Find it by clicking here.
Use Rocks for better drainage
Placing a layer of rocks at the bottom of a plant potter before the addition of soil is widely used as a method to increase soil drainage and aeration.
Rocks are generally used in addition to having holes at the bottom of the potter creates a height above the pant saucer so that water can drain out of the soil and not be well up at the bottom to create a waterlogging condition.
Consider Bottom Watering
Bottom watering is an alternative irrigation method to conventional top watering.
The plant is placed in a container of water reaching a height of 1cm.
The plant is allowed to sit for 15 to 20 minutes whereby the water is allowed to move up the soil via capillary movement.
Eventually, the water reaches the top of the soil where it becomes moist.
After the time has passed, the plant is then taken out and allowed to drain any excess water.
The use of bottom watering totally bypasses the entire problem posed by soil when it takes too long to absorb water from above.
Although this may work as a fix, the problem will still exist and you should still look into the reason why the soil isnt absorbing the water.
Using the above-stated solution will fix the problem so you can resume your normal watering program.
Additionally to bottom water you can also increase the humidity around the plant by misting.
Misting the plant increases humidity and causes the plant to absorb water through the leaves.
See a detailed article on how to properly mist plants here.
Water sitting on the surface of the soil is not a very common occurrence but when it happens it can be attributed to either soil surface tension or the soil composition.
By creating a routine watering schedule you can prevent soil from drying out and preventing water from being absorbed which normally happens when the soil has a peat mix.
A permanent fix is to remove the soil and use a more organic soil mix like compost while a temporary watering fix is to use the bottom watering method.