If you’ve ever considered building a garden out of cinder blocks, you may wonder whether they’re safe for the plants you plan to grow. After all, soil and concrete are two very different things, and chemicals don’t pair well with organic gardening.
Cinder blocks are not considered toxic to plants because they are made of concrete which is often a staple in gardening. There are better, more organic things you can put your plants in — such as terracotta, wood, or even ceramic pots — but a concrete cinder block is not necessarily harmful.
In this article, I’ll look at what makes cinder blocks toxic or not toxic to plants and how building with them can be beneficial for your garden bed. Additionally, I’ll go into the ways you can make sure your cinder blocks are ready for garden use.
The Safety of Using Cinder Blocks in Your Garden
There is little known about whether plants can absorb harmful chemicals from cinder blocks. The main concern with cinder blocks is that the chemicals in the concrete may seep into the soil and harm your plants. If this does happen, you’ll have to take immediate action to save your plants by removing them from their cinder block home.
However, this is unlikely. Most cinder blocks manufactured past 2000 are completely safe from materials like asbestos.
What Cinder Blocks Are Made Of
First, it’s important to define “toxic” in the context of your garden. Toxic might just mean something that can harm your plants, or it might mean something more specific. For the sake of this article, I’m assuming that you want to know whether a cinder block will have a chemical reaction with your plants and possibly cause them to die.
Cinder blocks are made of concrete, which isn’t necessarily a “toxic” chemical. This means that these blocks don’t contain any harmful substances that may leach into the soil and kill your plants.
However, you should be aware that some consider cinder blocks toxic because of the materials they have been made with pre-2000s. There could have been arsenic or asbestos in the cinder blocks, which was common for building materials before this time. As long as your cinder blocks are relatively new, you don’t have to worry about anything toxic in their composition.
Asbestos in Cinder Blocks
Asbestos is a naturally occurring mineral that was once used to make a variety of building materials, including cinder blocks. However, it was also discovered that asbestos causes cancer in humans and other animals when inhaled. As a result, many countries have banned the use of asbestos in construction products because it’s so harmful to human health.
Asbestos-containing cinder blocks may also be marked with an “AS” symbol or label on the bottom side of each block. You can tell if your cinder blocks are made with asbestos by checking for the abovementioned symbol or label or by having them tested. Check with your local health department for regulations in your area.
What To Do if You Think Your Cinder Blocks Are Toxic
If you’re worried about the toxicity of your cinder blocks, you can test them by sending a sample to a lab accredited by the National Voluntary Laboratory Accreditation Program (NVLAP). Contact the National Institute for Occupational Safety and Health (NIOSH) at 404-498-6160 or 800-356-4674 to determine if your local lab is NVLAP certified.
If testing shows that asbestos is present in your blocks, dispose of them properly. According to OSHA regulations, workers should wear protective gear when removing asbestos from homes or buildings, even if it’s just one block being removed from an otherwise safe building site.
If you need help disposing of any asbestos products in your home or garden (including cinder blocks), contact your local government agency for more information about regulations and disposal methods in your area.
Benefits of Adding Cinder Blocks to Your Garden
If you’re looking for an inexpensive way to build a garden bed on your property but aren’t sure if it’s safe for growing plants (like tomatoes), consider using cinder blocks instead.
The options available at hardware stores make them easy-to-use alternatives to traditional cement while still providing similar benefits:
- Cinder blocks will not crack over time the way concrete would.
- Cinder blocks are relatively lightweight compared to other materials like wood or metal, which makes transporting them easier.
- Their unique appearance adds character so no matter where your house is located, there’ll always be something interesting about it that could catch someone’s eye.
How To Prep Your Cinder Blocks for the Garden
If you’re building a cinder block garden, here are the steps to take:
- Remove the label from your cinder blocks. You can either soak it in water or use sandpaper to scrape off the label.
- Wash your new cinder block with a garden hose so that it’s clean and ready for planting.
- Use a wire brush (or some other abrasive material) to scrape one side of each block so that any loose paint chips off easily when you add soil later on.
- Let the cinder blocks dry. Once that’s done, you can add soil.
Creative Ways To Use Cinder Blocks in the Garden
Cinder blocks are more popular in gardening than you may think. In fact, many homeowners use cinder blocks as an alternative to traditional cement when building their own garden beds because they’re easy to work with and very affordable.
This YouTube video shows some neat ways to use cinder blocks to your advantage in the garden, which can be helpful if you have plenty of it on hand. The bench idea in this video would also be perfect for someone a little worried about toxic chemicals leaching into the soil (though, as discussed above, this is unlikely to happen):
How To Check the Health of Plants Grown in Cinder Blocks
If you’re not too sure about the origin of your cinder blocks, don’t fret. Clean them out first as described above, and just keep an eye on your plants. If it’s too late and you have some plants growing through your cinder blocks, you can look out for the following:
- Weak growth: If your plants don’t seem to be growing as tall or as large as they should, it may be a sign something is affecting their growth.
- Discoloration: Plants with strange colors might be under stress, possibly caused by toxicity in the soil.
- Rotting: If your plants are rotting, this may be another indicator that something is amiss.
There are dozens of other explanations for the above, such as underwatering or overwatering, an acidic or alkaline soil pH, too hot or too cold temperatures, and pests. However, if you’re worried you may have some asbestos or arsenic cinder blocks and your plants seem off, it’s best to play it safe and use a different material.
As I mentioned earlier, you can use terracotta, wood, or ceramic pots (which are less likely to contain harmful chemicals) as alternatives to cinder blocks for gardening.
Plants That Grow Well in Cinder Block Garden Beds
Not all plants can grow well in cinder block garden beds. Since cinder blocks provide little (if any) space to grow, they’re best for relatively small plants. Fortunately, many plant ingredients used in food (like shallots and garlic) are able to grow in cinder blocks.
If you plan to grow bigger varieties, you naturally won’t be able to use every hole in your cinder blocks. For example, if you’re growing broccoli or cauliflower (which have pretty wide leaves), you need to plant them a couple of feet apart, at least. Otherwise, you’ll risk overcrowding them.
Conclusion
Whether you’re gardening with cinder blocks, it’s important to be aware of the risks. The best way to minimize risk from cinder blocks is to use the ones manufactured post-2000. You should also keep your plants away from the soil for a few months after building your cinder block bed.
If you want to use cinder blocks method for gardening purposes without the risk of leaching chemicals into your soil or having plants absorb harmful chemicals, consider using them in combination with other materials like dirt when building beds.
