Although transplanting a new plant with friends is one of the many joys of gardening, I realized some plant owners and gardeners are usually unsure about their potting mix. In fact, many gardeners aren’t sure if it’s okay to put sand in the bottom of a planter.
You should not put sand in the bottom of a planter, as the drastic change in soil texture and particle size can reduce drainage. Instead, sand must be mixed evenly with the potting mix components to improve soil drainage, enhance soil aeration, and reduce complications due to overwatering.
You also need to monitor the sand type, quality, and quantity to ensure it doesn’t hurt your plant in the long run. These are critical factors you must consider before you fill your planter because while plants don’t mind growing in some sand, different species have specific needs. In this article, I’ll explore all of these and then teach you how to fill your planter to ensure your potted plants thrive in any environment.
Why People Put Sand in the Bottom of a Planter
Every gardener and plant keeper knows that the secret to growing healthy and beautiful plants (including vegetables) is to control every environmental factor involved in the process.
One of the most important factors for growing plants successfully is soil quality, which involves soil drainage. Adequate drainage protects your plant’s roots from life-threatening risks brought about by overwatering, such as root rot.
Sadly, such a condition can often be irreversible once the symptoms appear. That’s why many gardeners devised numerous ways to reduce the risk of overwatering. One of which is adding a layer of sand or other coarse materials like pebbles and gravel in the bottom of the pot.
At first thought, it might seem like a good idea because sand, in fact, has excellent drainage. People over the decades (or centuries) have been passing on this idea to fellow gardeners, believing that it can improve soil drainage in pots.
However, in reality, creating multiple layers of soil with varying particle sizes can result in extended moisture retention within the plant’s root zone. Scientifically, water will saturate the denser soil layer first before moving on to the loose layer. In essence, this does not improve drainage.
If you’re putting sand in the bottom of your planters, you’re wasting precious material. If you want to improve drainage, you will achieve better results by mixing the sand with the dense potting mix. This will create an evenly saturated soil structure that can support the growth of the plant roots.
Also, remember to use horticultural sand to get the best results.
Sand Qualities and How They Affect Plant Growth
It is rare to find plants you can grow in pure sand, but you can grow a wide variety of plants, including vegetables, in soil or potting mixes with adequate amounts of sand. This is because of sand’s inherent qualities which can affect plant growth in different ways.
Here are some vital sand qualities to remember:
- Excellent drainage
- Heat retention
- Abundant and larger pore spaces
- Inability to hold nutrients
I’ll discuss these qualities in more detail below and explain why placing them at the bottom of your planter isn’t beneficial.
Excellent Drainage
A plant can absorb moisture from the soil only for a short time and once it has absorbed all that it needs, the remaining water will sit in the soil until it drains out or evaporates. As the roots stop absorbing water, the excess moisture will become available for consumption by soil microbes, which can sometimes be harmful to your plants.
With enough exposure to water, these microbes can proliferate to dangerous numbers that can inflict physical damage on your plant’s sensitive roots. That’s when the roots decay and prevent further nutrient or moisture absorption.
That said, it’s crucial for the potting mix to have adequate drainage to preserve your plant’s health.
It’s no secret that sand has excellent drainage because water can navigate through coarse sand particles more quickly. So why doesn’t putting this material at the bottom of the planter improve drainage?
Imagine having two planters with the following soil setups:
- A is an even mix of coarse sand and fine soil.
- B is an upper layer of fine soil and a lower layer of coarse sand.
When you pour water on them, you’ll notice different results. In planter A, the water will trickle evenly throughout the soil mix and out of the drainage hole because the surface has an even distribution of pore spaces.
On the other hand, in planter B, water will navigate through the narrow pore channels within the fine soil before hitting the coarse layer where it will likely spread laterally instead of downward. This zone then becomes saturated.
Without sand or coarse materials at the bottom of the pot, the water will pool in the soil at the bottom of the container, creating a water table or an area that divides the wet soil below from the moist soil above.
Since there’s enough unsaturated soil above the wet area, your plant’s roots have enough space to grow safely without risking root rot.
However, when you place sand at the bottom of the planter, water will still pool at the bottom of the fine soil layer. This elevates the water table and brings it closer to the roots. The reduced amount of fine soil also reduces the area the roots can grow safely into.
It is the root zone that should have adequate drainage, not the bottom layer of your pot. That said, placing sand at the bottom of your pot proves counterproductive.
Heat Retention
Sand has good heat retention capacity, making it an excellent substrate for seeds or young plants. Most seeds germinate better in warmer soil so having a good amount of sand in your seed-starting mix can improve germination rates.
Warm-season plants like corn also grow faster in their early stages when started in sandy soil. Sunflowers also like warm soil.
Confining the sand at the bottom of the pot beyond the reach of the roots can deprive your plants of this beneficial quality.
Abundant and Larger Pore Spaces
Plant roots also need enough pore spaces in the soil to access both water and oxygen. In addition, sufficient airflow within the soil can help remove excess moisture through evaporation.
So if the upper layer of the soil is dense and the sandy layer is way beyond the reach of the roots, there’s really no benefit in adding sand to the planter.
To reap these benefits, the only way to go is to mix the sand with the denser soil material.
Inability to Hold Nutrients
Sand is unable to hold onto nutrients as well as other soil types, making it nutrient-poor. So although it does help with aeration and drainage, it won’t contribute much to the plant’s nutritional requirement.
However, an evenly distributed sand-and-fine-soil mix can spread the nutrients more efficiently throughout the root zone instead of confining it within one area and causing fertilizer burn to the roots.
While most sand types share more or less the same qualities listed above, they can affect plants differently, depending on what type of sand you’re using.
Understanding the Different Types of Sand for Planters
Although this might come as a surprise, most plant keepers and gardeners don’t worry too much about the soil they use for their plants, especially when growing them in planters. After all, it’s relatively easy to control the environment of potted plants, and you can get sucked into keeping track of other essential metrics like temperature and humidity, neglecting your soil quality.
And while diligent gardeners focus on soil moisture content, aeration, and essential mineral levels, you must also consider precisely what kind of soil you use for your plants.
As discussed, it’s an excellent idea to work the sand into your potting mix to help improve soil aeration and drainage. However, not just any sand will do if you want to keep healthy potted plants. So it’s necessary to examine the qualities of each sand to determine if they’re suitable for you and your plants.
Here are three main types of sand you can use for gardening:
- Builders’ sand
- Grit
- Horticultural sand
Let’s quickly explore what separates these sands from one another.
Builders’ Sand
Builders’ sand is probably the most familiar and comes to mind when most people think of sand. As its name suggests, its primarily used by masons and the construction industry for building materials. Therefore, some people also refer to builder’s sand as masonry sand.
However, regardless of what it’s called, all builders’ sand share the same properties. The sand has fine yet coarse grains that allow slow drainage. Therefore, they can hold water for longer and are excellent for plants that prefer moist soil.
Most gardeners typically use builders’ sand as parts of potting mixes instead of as layers since it doesn’t have the usual qualities for bottom soil. Still, you can use the sand if you don’t want to water often and if the plant doesn’t mind prolonged exposure to moisture.
And while builders’ sand shares some similarities with play sand, they’re not the same. So, I don’t recommend using play sand in your pots or gardens for whatever reason since it can be harmful to your plant’s health.
Grit
Grit or sharp sand is pretty similar to builders’ sand in many ways. However, its grains are larger, heavier, more coarse, and sharper than the latter, making it perfect for concrete mixes. Grit typically comes in the traditional brown color of most sand, but it has more drainage properties than builders’ sand.
So while it’s the optimum choice for professional landscapers and builders, you can use it in your garden to improve soil aeration and drainage.
The sand is also referred to as river sand and builders’ grit in some circles since it’s the optimal choice for construction projects in wet areas.
Horticultural Sand
The best way to describe horticultural sand is as medium grain sand with medium-fine particles specifically designed for plants and planters. It’s commonly known as potting sand and is used to optimize soil drainage and aeration.
Horticultural sand is the best type for planters and is pretty easy to recognize. The sand is as coarse as grit and consists of small and large particles of varying sizes. It’s usually crushed-up sandstone or quartz, but granite works just as well.
In addition to its excellent drainage and aeration, horticultural sand also helps balance soil pH since it’s mostly inert particles. Therefore, you can use it as an ideal base soil for plant mixes.
And since the sand does not clump together when wet, it’s suitable for planters and plants in any climate.
You can also use horticultural sand as a mix instead of as a layer. In this situation, I recommend you combine it with poorly draining soil so that the result is perfect. You can also pair the sand with mulch to help control drainage even better.
In fact, horticultural sand is so helpful in gardening that most potting mixes contain it to some extent. Therefore, I recommend using this sand in your indoor garden.
Final Thoughts
Sand is an excellent resource in gardening and plant keeping, and you can use it to improve soil drainage and aeration. However, you must use the correct soil type and mix it evenly with your potting soil to get excellent results. Of course, it’s also vital to consider the amount of sand in the planter to ensure your plants thrive as much as you want.
