Healthy plants are a gardener’s delight. But with a potted plant, several issues can arise, especially when it comes to soil composition and volume. In such situations, you might find yourself wondering whether you should add more soil to your potted plant.
You can add more soil to a potted plant when the soil in the pot has shrunk. However, if the soil keeps sinking due to microbial activity, decaying organic matter, watering, and compaction, it is best to repot the plant instead of adding more soil to the potted plant.
In this article, I’ll explain why potted plants may require more soil added to the pot. I’ll also tell you if it is best to keep adding more soil to a potted plant or whether you should repot it altogether. Lastly, I’ll provide some tips on how to keep your soil in good shape to ensure your potted plant thrives.
Why You Would Need To Add Soil to a Potted Plant
Experts in container gardening will tell you to leave at least 1″ (2.54 cm) space between the plant pot rim and the top of the soil inside the pot. This space is crucial for proper plant watering. If your plant pot is topped with soil, the water will be running over the pot edges and won’t sink properly into the plant roots.
But what if the one-inch (2.54 cm) space between the soil top and the plant rim seems to be growing bigger with time?
Unfortunately, that is a sign that something is happening to your plant soil and that you may need to take action to prevent the situation from worsening. Adding more soil to your potted plant may be required in this case.
Here are the top 5 reasons your potted plant soil is sinking:
1. Hardened Soil Due to Microbial Activity
Soil is rich with microorganisms such as fungi, bacteria, and ground insects. In a typical garden, these microorganisms provide the health and balance required by soil. As such, a gardener may not need to worry too much about soil health for their garden.
In potting soil, however, the action of soil microorganisms is altered. As a result, the soil in a pot is gradually impoverished when plants use nutrients, and organic material decomposes in the soil.
Over time, the potting soil with consumed nutrients and diminished organic material becomes harder as its pore spaces close, which gradually blocks air and moisture passage. If the situation remains unchanged, the soil will begin to sink whenever the plant is watered.
Adding new soil to the pot will be a good move if the soil in the pot still supports plant growth. You should mix the new soil with the old to create a quick solution to the aeration and drainage problems.
2. Decaying Organic Matter
When you use soil to grow plants in pots, you usually enrich it with organic matter, fertilizer, or other organic soil enrichers like compost or worm castings.
Added organic matter in soil decomposes gradually and is converted into plant nutrients. Once the organic matter is consumed, only hard, nutrient-free soil is left in the pot. Hard soil minus organic matter is the reason why the level of soil in your pot shrinks.
Adding more soil with organic matter to your potted plant will replenish the soil level and provide your greenery with more nutrients.
3. Washing Away Soil With Watering
Plant pots have a hole (or many holes) at the bottom to improve drainage and counter plant rot due to waterlogging. If the soil in your plant pot has high porosity, and the pore spaces are too wide, it will most likely allow water to run down easily and quickly. This also means some of the soil will be washed down with water. With time, the soil level in your plant pot will shrink.
Sandy soils have the highest porosity and can be improved by adding another type of soil with better porosity to your plant pot. This will not only raise the soil level but also improve soil drainage and nutrient content.
4. Replacing Soil With Organic Matter
If some of the soil from a plant pot is replaced with organic matter, then the soil level will shrink at some point. This will happen as the added organic matter decomposes and turns into humus.
In this case, adding new soil again is recommended. You can also add new organic matter without adding new soil, but the soil level will sink again once the organic material decays. Adding a mixture of new soil and organic matter is highly recommended if you want to maintain a good volume.
5. Soil Bulk Density and Compaction
Soil bulk density is its dry weight per unit volume. It takes into account both the solid matter and the pore spaces in the soil.
Loose and porous soil types like sand have lower bulk densities but higher porosity than tightly packed soils like loam and clay. Soil with a high bulk density is more compact because the soil particles are close together.
In both low and high-bulk-density soils, a decrease in organic matter, coupled with pressure when watering, can push air out of the soil and reduce pore space, which gradually causes soil compaction.
Adding new soil into the plant pot and mixing it with the compacted soil will improve soil pore space. Consequently, the recommended soil level in the pot will be maintained.
While we’ve suggested adding more soil to a plant pot that has sinking soil, the question of whether you should keep doing this over and over again still begs.
Should You Keep Adding Soil or Repot a Plant?
You can add more soil to your potted plant to improve its nutrient content, aeration, and drainage. Adding more soil to your potted plant should be considered when the plant is still in good condition.
Nonetheless, adding more soil to your potted plant over and over is not a lasting solution to the problem you might be trying to solve.
As such, if the soil in the pot is depleted and the plant is showing signs of poor growth, replacing potted plant soil entirely or repotting a plant is recommended.
Signs of poor plant growth include:
- Dying, falling, yellow, or withering leaves.
- Protruding or circling roots.
- Roots pushing up the plant and nearly out of the pot.
- Stagnated growth.
Before your plant can reach the point of needing additional soil or being repotted, you can also take some measures to prevent the soil from shrinking, as explained in the next section.
How To Counter Potted Plant Soil Sinking
Since soil sinking is a primary reason for adding more soil into a potted plant, a few tips for preventing soil sinking in plant pots are opportune:
- Use good quality soil right from the beginning. Loam soil has a balance of sand and clay and will give the best results when it comes to soil aeration and drainage. You’ll remember that poor soil aeration and drainage cause soil compaction, which reduces the soil level in the pot.
- Ensure enough organic content in the potted plant soil. Do this by adding organic matter to the potting soil. Organic matter for potted plant soil can include animal manure such as cow dung, compost, dead leaves, grass clippings, or coir fiber.
- Add coarse material to the potted plant soil. Course matter in the soil increases pore space and counters soil compaction. You can do this by ensuring that course material makes a third of the potted plant soil.
- Use a watering can with tinier holes. If soil compaction is caused by high-pressure watering, avoid using a watering can with a large outlet. Instead, use one with smaller holes to avoid too much pressure on the soil. Alternatively, switch from top to bottom watering. You can read my guide on bottom watering here: How to Water Plants from the Bottom (Beginner’s Guide)
- Aerate the potted plant soil. You can improvise a tiny raking tool using a kitchen fork or chopsticks to gently turn the soil in the plant pot. Turning the soil improves aeration and drainage and controls soil compaction. You can learn how to aerate soil in potted plants in my other article: How to Aerate Soil in Potted Plants (Easy Guide)
- Avoid compacted soil by patting the plant pot once in a while. If you see that the soil in your plant pot is beginning to compact, pat the pot on the sides to loosen the soil. Loose soil has better aeration and drainage and can preempt soil sinking.
Again, if you’ve taken these measures previously, but your plant still seems to need more soil added to the pot, the next best solution is repotting the plant.
Should you keep adding more soil to a potted plant? You can add more soil to a potted plant once or twice. However, you should not keep adding more soil to a potted plant over and over.
If your potted plant has sinking soil, the soil’s pore space is likely compromised by poor aeration or drainage, meaning adding more soil isn’t advisable. The shrinkage could also be caused by a lack of organic matter, which makes the soil hard while reducing its overall volume.
Instead of adding more soil to a potted plant time and again, consider repotting the plant to improve its growth and overall health.