Lightweight concrete planters, also referred to as GRC (Glass Reinforced Concrete) or lightweight cement pots, have become an increasingly popular choice for our clients at Sigma Planters. So much so that you will see our most extensive range of shapes and sizes is available across two of our core and most popular ranges, called Florence and Milano.

In this article, we will be answering some of the most frequently asked questions about concrete pots so you can make an informed decision about whether they’re right for your landscape architecture and design project.

Are Concrete Pots Good For Plants?

Concrete can negatively impact plant growth due to its alkalinity, especially when new. It can leach lime, which lowers soil pH. This can be detrimental to plants, as many species thrive in a slightly acidic to neutral pH range.

The alkalinity of concrete can interfere with the absorption of essential nutrients by plant roots, even if those nutrients are present in the soil.

This can be avoided by sealing the concrete. Sigma Planters concrete pots are over 90% fiberglass and really only look like concrete, since fiberglass is stronger and better in all aspects.

How Does Concrete Affect soil pH?

Natural concrete can leach lime, which decreases soil pH and can harm plants until the concrete is aged or waterproofed. Sigma Planters concrete-look fiberglass planters are pre-sealed, preventing pH imbalances and creating a neutral planting environment ideal for healthy plant growth.

Are Cement Pots Waterproof?

Concrete pots can be made waterproof with a sealant, but it’s important to keep in mind that they are naturally porous. This means that they will absorb water over time, so it’s essential to ensure they are properly sealed if you plan to use them for plants requiring a lot of moisture. All Sigma Planters are pre-sealed so all you have to do is add quality potting mix and plants.

Why Do Cement Pots Crack?

Cement pots can crack for a variety of reasons, including changes in temperature, exposure to the elements, and improper curing. It is important to keep concrete pots in a protected area and make sure they are allowed to cure properly before use. Sigma Planters solves this problem by using a high quality fibreglass core with a robust concrete finish that is guaranteed not to crack.

Is Cement Poisonous To Plants?

No, cement is not poisonous to plants. However, it is important to make sure the concrete pot you choose is made with safe and non-toxic materials, as some additives can be harmful to plants and soil. Again Sigma Planters tick this box as well.

Can Plants Break Through Concrete?

Yes, it’s possible for plants to break through concrete, especially if the concrete is of poor quality or if the planter lacks proper drainage. Over time, aggressive root systems can exploit weaknesses in the concrete, leading to cracks and potential damage to the planter.

Sigma Planters are engineered to prevent this issue. Our planters feature built-in drainage and raised feet to ensure optimal plant health. Unlike many concrete planters, Sigma Planters are guaranteed not to crack, providing a durable and long-lasting home for your plants. By choosing Sigma Planters, you’re investing in a planter that prioritises both the well-being of your plants and the longevity of your outdoor space.

How Do You Take Care of Concrete Pots?

Taking care of concrete pots is relatively simple. To maintain their appearance, it’s important to clean them regularly and keep them sealed to prevent water absorption. An annual stone or fibreglass wax sealer is recommended. 

Do Concrete Pots Need Drainage Holes?

Yes, concrete pots should have drainage holes to prevent water from becoming trapped and damaging the roots of your plants. If the pot you choose does not have drainage holes, you should drill some yourself to ensure proper drainage. 

What is The Difference Between GRC, Concrete, and Fibreglass

GRC (Glass Reinforced Concrete), concrete, and fiberglass are distinct materials with different compositions, properties, and applications. Here’s a breakdown of their key differences:

Concrete:

Composition: Concrete is a composite material primarily consisting of:
Cement: A binder (usually Portland cement) that reacts with water to harden. Typically makes up 10-15% of the mix.
Aggregates: Inert materials like sand (fine aggregate) and gravel or crushed stone (coarse aggregate) that provide bulk and strength. These constitute the largest portion, around 60-75% of the volume.
Water: Essential for the chemical reaction (hydration) with cement and to make the mixture workable. Usually 15-20% of the mix.
Admixtures (optional): Chemicals added to modify properties like workability, setting time, strength, or durability.

Properties:

• High compressive strength (resistance to being squeezed).
• Relatively low tensile strength (resistance to being pulled apart) and flexural strength (resistance to bending).
• Can be very heavy.
• Susceptible to cracking, especially due to shrinkage during curing and tensile stresses.
• Alkaline in nature, which can affect some plants.
• Can be porous if not properly sealed.

Applications:

Foundations, structural elements (beams, columns, slabs), pavements, walls, and various other construction purposes.

GRC (Glass Reinforced Concrete):

Composition: GRC is a composite material made of a cementitious matrix similar to concrete, but with the addition of alkali-resistant (AR) glass fibers. Typical components include:
Cement: Similar to concrete.
Fine Aggregates (Sand): Similar to concrete.
Alkali-Resistant Glass Fibers: Short fibers dispersed throughout the mix, typically making up 2-5% by weight. These fibers significantly enhance tensile and flexural strength.
Water: Similar to concrete.
Polymers and other Admixtures: Often added to improve workability, strength, and durability.

Properties:

• Significantly higher tensile and flexural strength compared to traditional concrete due to the glass fiber reinforcement.
• Lighter than traditional concrete because it can be produced in thinner sections.
• More resistant to cracking and impact.Greater design flexibility, allowing for complex shapes and thinner profiles.
• Can still be alkaline, but the effect can be mitigated by sealing.
• Durable and weather-resistant.

Applications:

Architectural facades, cladding panels, decorative elements, planters, furniture, and other non-structural or semi-structural applications where a lightweight and strong material with design flexibility is needed.

Conclusion

Lightweight concrete planters offer a compelling blend of durability and style for gardeners and landscape architects. These pots provide a sturdy and aesthetically pleasing option for various planting projects. However, it’s essential to consider factors such as proper drainage and maintenance to prevent potential issues like cracking. By understanding the benefits and drawbacks of concrete planters, you can make an informed decision for your specific design needs.