Worried that your concrete planter is bad for your plants? The answers and the fix!
Whenever I create a tutorial on how to make a concrete planter, the question I am asked most is – “are concrete planters safe for plants?”.
The short answer is yes, plants can be safe in concrete planters. But there are things you may need to do to prepare the concrete pot before planting certain types of plants.
Plants are finicky creatures, as you know, it’s very easy to overwater or underwater a plant. If they don’t have proper sunlight, they can die, but plants can also easily be burned by too much sun.
And if things are complicated enough, plants also have a preference for the composition of soil and a for the pH of the soil.
Yikes, it’s amazing that as many potted plants actually do just fine with all these complicating factors, isn’t it?
Please refer to the Plants In Concrete Planters FAQ at the bottom of the page, after reading.
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Are Concrete Planters Safe For All Plants
Concrete can be harmful for some plants because most cement and concrete mixes contain lime. And lime is the culprit that raises concern as to whether it’s safe to grow plants into cement and concrete pots.
Though not toxic, lime has a high pH level, making it highly alkaline. Some plants won’t prosper or even survive in soil with higher alkalinity.
The reason there is lime in most concrete mixes is because most US manufacturers of concrete and cement, use portland cement as the base material for their branded mixes. Portland cement contains lime.
Then they will add other minerals and compounds to it for various reasons like to increase strength, increase working time, or to shorten curing times.
Though there are probably more plants that need acidic soil, you’ll be happy to know, there are plants that need an alkaline environment.
Succulents are a great example of alkaline-loving plants and thrive in higher alkalinity. They are a great fit for planting in a concrete or cement planter.
Other than most succulents, here are some other plants that do great in concrete pots because of the pH of the soil:
- African Violets
- Morning Glory
- Easter Lilies
And even vegetables and herbs like:
- Cabbage Chives
This article has a much longer list of these alkaline-friendly plants.
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Currently, I have 21 cement or concrete planters that have plants in them and most are succulents. To see these, take a look here for the tutorials on 21 Unique Concrete Planters You Can Make.
I didn’t use a leaching process for any of them, and only one of them is sealed.
When I tested my soil, I found that the pH range is 7-8. For reference, a pH scale is measured 0-14. 7 is neutral and below that is acidic and above that is alkaline.
However, these tests were done months after the plants were potted.
It’s when concrete is fresher or more recently cured, that the higher amounts of alkalinity leach through. So the pH may have been higher shortly after potting.
My succulents, for the most part, have thrived in these planters.
Note: Please refer to my sealing test showing the evaporation differences in sealed cement vs. unsealed, as well as soil water discoloration in sealed planters.
Making Concrete Planters Safe For Plants
However, if you want to make a DIY planter from concrete or cement, and your plants are types that prefer acidic soil, then hold tight because there are easy fixes for this.
First, you can change the pH of your soil by adding sphagnum moss, iron sulfate or organic mulches.
This doesn’t always work well, but there are easier and more sure fixes.
The best solution for keeping plants healthy in concrete planters is to soak the planter in water for three days. Soaking the cement or concrete will quickly leach the alkalinity out of it. More on this below.
Some people will just leave their planters out in the rain for a few days before planting.
Manually leaching out the alkalinity is likely good enough, but if you want to be extra safe, then you can seal them.
Based on my sealer tests, I found this concrete sealer to be the best choice for a concrete pot.
You can also skip the water leaching process and just seal them, this should be effective enough.
Now before you seal your planter, take into consideration that the great thing about a concrete pot isn’t just that they are beautiful, but they also serve an important function.
Concrete and cement planters in their raw form (unsealed) are porous. Having a porous material is a benefit to plants as it helps control overwatering.
Concrete really is the best choice of material for a planter.
If you seal the planter you will be making it non-porous. But there are other good reasons for sealing concrete, which is that it will help reduce efflorescence.
Efflorescence is the white residue that you see coming through cement after soil comes through. It’s the minerals in the soil that can leave this residue.
Sealing a cement planter can help preserve the longevity of the pot, as well as protect any added color. This is the same whether added to the mix or colored after the cement has cured.
It’s up to you whether or not you want to seal your containers. My opinion? If you are planting succulents in them, there’s no need.
If I were to pot plants that need acidic soil, I would simply soak them in water and still leave them unsealed.
What about concrete planters bought from a store, are they safe for plants?
It is very likely that these have already gone through a leaching process and soaking them in water isn’t necessary. It is also likely that the planters are already sealed.
Do you want to know how to make a concrete planter from start to finish, then check out the How To Make Concrete Planters- Everything You Need To Know, which has everything you need to know about making them!
Pocket Guide to Concrete & Cement Mixes For Crafts
Quick Steps For Making Concrete Planters Safe For Non-Alkaline Loving Plants
OPTION 1 | APPLY A SEALER TO THE CONCRETE TO REDUCE ALKALINITY
Seal the planter inside and out using either acrylic paint or a concrete sealer. Seal it both inside and outside using a foam brush to apply it.
Keep in mind that you have made the cement planter non-porous by doing this, which is one of the benefits of using a cement planter.
OPTION 2 | REDUCING CONCRETE ALKALINITY VIA LEACHING
Soak the planter in water for three days before potting the plant. This will be effective at reducing alkalinity. Also, be sure to refresh the water each day.
You do not need to seal this, but if you would like to, then be sure to let the cement or concrete fully dry.
OPTION 3 | Change The Soil Composition To Reduce Cement Alkalinity
Add sphagnum moss, iron sulfate or organic mulch.
Or do a combination of each of the above steps.
For a great article on the benefits of different types of pots for plants, check out the Micro Gardener’s article. It offers information on choosing the best container material for your pots, not just concrete.
And this article explains the differences between six concrete mixes and which one is best for cement crafts like planters.
To see some of my concrete planter tutorials, you can check these out-
Concrete Planters And Plant Health FAQ
Concrete is not actually toxic and is not toxic to plants. That said, concrete can potentially be harmful to some plants.
The reason for this is because concrete contains lime which is highly alkaline. Many plants can’t thrive in soil that has high alkalinity and instead need soil that is more acidic.
Most concrete planters that are purchased at stores are safe for any plants because they likely have gone through a leaching process and have been sealed.
If you want to be safe, you can leach out the alkalinity by soaking the concrete planter in water for three days.
Cement is good for plants like succulents.
In general, both concrete and cement are fantastic options for potted plants because they are somewhat porous and will allow some moisture to get through.
This makes plants easier to maintain because it’s much less likely you will overwater them than if they were in a planter that is plastic or any other non-porous material.
Cement and concrete are the same in terms of which is more suited for plants. They both contain lime and will leach alkalinity.
You can neutralize concrete by soaking it in water for about three days. Soaking concrete or cement in water leaches lime through the pores.
The benefit of doing this is that some plant types may not thrive, or even could eventually die, due to high alkalinity. You see, lime has a high pH, making it very alkaline.
However, plants like most succulents, often thrive in soil with a higher pH and so leaching a concrete planter or pot, isn’t necessary.
It is safe to grow vegetables in concrete pots, planters and containers. However, if you are making these yourself, you should leach them for three days.
Typically concrete planters that are purchased from a store will already have gone through that process and are also very likely to be sealed.
So you can feel safe planting vegetables in concrete and cement pots.
The best plants for concrete planters are succulents.
This is because succulents like soil that is more on the alkaline side and concrete leaches lime which is highly alkaline.
However, you can plant any type of plant in a concrete planter, but you may want to soak it in water first.
Do this for three days and change the water out each day. This will speed up the process of leaching out the alkalinity.
If you are still concerned about high alkalinity, you can choose to seal the concrete planter in addition to soaking them in water.
Concrete pots only need to be sealed if you are growing a plant in the pot that needs more acidic soil.
You see, concrete contains lime which can cause the soil to become alkaline.
This is a good environment for succulents, but many plants will not be happy in this soil.
Sealing the concrete will help prevent some of the lime from leaching into the soil.
However, I recommend soaking the pots in water for three days before sealing. This will quickly pull much of the alkalinity out of the concrete.
And then follow it up with your sealer.
Another benefit of sealing a planter is to prevent efflorescence. Efflorescence is caused by the minerals in concrete leaching through and causing a build up of white residue.
Sealing them can eliminate this or at least reduce it.
The best concrete sealer for planters will depend on what your end goal is. The reason for sealing a concrete planter is for two reasons.
One is that it can make the concrete a little more durable and the other is to help prevent the leaching of lime, which is an ingredient in most concrete and cement products.
This is the concrete sealer I typically use when sealing concrete.
The issue with lime is that it is very alkaline which can harm plants who by nature, like to grow in soil that is more acidic.