Is It Safe To Use Cinder Block Raised Garden Bed

Updated September 21, 2021

Many beginning gardeners plan to grow their vegetables in raised beds — and for good reason! Those of us who have been raised bed gardening for years testify to how much we enjoy it! What's so great about gardening in raised beds?

Better harvests
Less weeding
Sharp aesthetics
Better Control Over Soil Fertility
Uses Less Water & Mulch
Easier to work in
Less compaction = more airspace in soil = healthier plants

What's not to love?

But as in any venture, mistakes are common. The problem with making mistakes in a raised bed garden is they aren't easily corrected. I know this first-hand!

Had I known as a beginning gardener what I know now a decade later, I would have done many things differently. But thankfully, I've been able to correct many of my own raised bed mistakes. Others I've learned to live with, but now I know!

From both my own experience and from hearing the experiences of others, I've compiled these mistakes raised bed gardeners commonly make. (Number four is the biggest one, in my opinion.)

If you're planning a raised bed garden for the first time or adding to your existing beds, this article will help you avoid many of the mistakes I and others have made.

And if you're already gardening in raised beds but are seeing lackluster results, you may find some reasons why here.

*some links below are affiliate links, which means if you click through and make a purchase, I receive a small commission.

1. Raised Beds are too wide.

One of the biggest benefits of raised bed gardening is avoiding soil compaction. You want to be able to work in your garden beds without stepping on them.

Most beginners don't realize this, but healthy soil needs air as much as it needs water! But when soil is trampled upon by either machines or foot traffic (or both!), the air between the soil particles is pushed out.

To avoid this problem, we want to make every effort NOT to step on our garden beds. This promotes a better soil structure and ultimately healthier plants.

But if the width of your raised beds prevents you from working all sides within your reach, you will find yourself stepping inside the bed, defeating this major benefit of a raised bed.

For this reason, raised beds should never be more than four feet wide.

Most people can comfortably reach into the center of a four-foot-wide raised bed without any problem. But as I've experimented with different sizes, I've found a three-foot-wide span is even more comfortable for me.

When choosing the width of your raised beds, you also must consider the placement of the bed. I made the mistake of putting two 4′ by 12′ raised beds up against a fence. Not only did weeds and grass grow between the beds and the fence, but I could not reach into the back of my bed to easily plant, weed, or harvest.

raised bed by fence — See how close the electric fence is behind these raised beds? Big mistake.

This was such a pain we ended up moving the fence.

Learn from my mistake here: if you situate your raised beds next to a fence, I recommend the width not exceed thirty inches. This way, you can work your bed from one side only with ease.

jalapeno peppers in raised bed — This bed is 2.5 feet wide, which makes it easy to work from one side if necessary.

2. You don't plan for irrigation.

Unless you want to hand-water your raised beds with a watering can (and that will get old quick), you need to plan ahead of time how you will irrigate the beds.

First, I recommend placing raised beds near a water source. Whether you plant to hand-water your beds or use a more efficient system of soaker hoses or drip lines, having water easily accessible will save you much time and headache.

In my early years of gardening, I placed a lawn sprinkler near my raised beds to overhead water my garden. But this proved entirely inefficient. Not only did overhead watering waste water, but it also exacerbated many of the fungal diseases common in my area like early blight and powdery mildew.

(Here's a more thorough discussion I had about garden irrigation with Joe Lamp'l.)

Now I recommend soaker hoses or drip irrigation for raised beds. For just a few raised beds, soaker hoses will perform just fine.

But if you have more than a few raised beds, or if you garden with a combination of raised beds and ground beds like I do, setting up a drip irrigation system works great and costs less.

Here is an inexpensive soaker hose as well as a drip irrigation starter kit similar to what I use in my garden.

3. Wood (or other material) is Unsafe.

Though you will find a myriad of speculation about the safety of certain pressure-treated wood for use in raised beds, most experts agree on this: do not use pressure-treated wood manufactured prior to 2003.

Pressure-treated wood manufactured prior to 2003 contains chromated copper arsenate, and you don't want that near your food garden.

What kind of wood should you use for your raised bed?

If you want to build your raised beds out of wood, these are the three most common options:

Pressure-treated pine
Untreated pine (or similar)
Rot resistant wood (like cedar)

Pressure-Treated Wood

First, let's talk about pressure-treated pine. Full disclosure, this is what I use. Modern methods of pressure-treated wood use safer practices than those used prior to 2003.

After researching this topic at length, I believe any risk in using pressure-treated wood for raised bed gardens is minimal. Copper is the main substance used in modern pressure-treated wood, and copper is actually a nutrient plants need in small amounts.

Therefore, in my opinion, if enough copper leached into the soil to pose a health hazard, we would see it first in the health of the plants. The plants themselves would suffer. In my decade of gardening in raised beds using pressure-treated wood, I've never seen a plant suffer in this way.

But what about leaching that does occur? The studies that have been done (and admittedly, there are few) on pressure-treated wood in raised gardens have shown a larger amount of copper leached near the wood itself than is present in the rest of the soil. Though it's a minimal amount, I plant my crops several inches from the side of the bed.

Using pressure-treated wood in raised beds is definitely a personal choice. Personally, I choose it because I can build more raised beds and grow more food with the same amount that I would pay for a more expensive rot-resistant option (more on that below).

But, not everyone will come to the same decision. If that's you, what are your other options?

Untreated Pine

Some gardeners choose to purchased untreated pine, mainly because it's less expensive than other untreated wood.

Though I've never used this, from what I understand, the life of untreated pine is very short — perhaps a few seasons. This likely depends on the amount of rainfall your location receives, as rainfall will contribute to the breakdown of the wood.

This may be an option for you if you plan for your beds to be temporary and you want to save money.

Rot-Resistant Wood

Many people choose to use rot-resistant and chemical-free woods such as cedar or redwood. These beds are truly gorgeous, and they can last many years.

The problem? All good things come at a price. When I prepared to build my elevated raised bed, I compared the price of pressure-treated wood to cedar, and the cedar would have cost me (at the time) two to three times as much.

For one small bed, the difference in price may be worth it, especially if you still have concerns about pressure-treated wood. For me, though, and the size of the bed I was building, the difference in price was in the hundreds of dollars, if not nearing the thousands.

One thing to note — the price and available of rot-resistant woods depends on your location. You may have a ready source of rot-resistant wood nearby, so it's worth looking into and pricing yourself.

Cheap Raised Bed Option

If you're looking for cheap raised garden beds, you might want to repurpose wood that was used in a different capacity. Perhaps you have an old fence you are taking down, for example. To be safe, just make sure it wasn't manufactured prior to 2003.

My brother-in-law called me when he took down his old fence and asked me if I wanted the wood. Before I took it, I confirmed the fence was only 10 years old. Then, I repurposed that old fence into three new raised beds. You can see my process of building these raised beds from that old garden fence here.

Other Materials for Raised Beds

These days gardeners are getting innovative and are using a variety of materials to grow their vegetable gardens. While you always want to stay away from old tires or railroad ties, here are safe options to consider:

Raised Beds constructed from steel panels (like Jill Winger's raised beds here).
Metal raised beds (like Birdies raised beds – get 5% off with code JOURNEYWITHJILL)
Rocks (like Elliott Homestead uses here)
BPA-free polyethylene pre-built raised beds (from Good Ideas, Inc. – get 10% off with code JILL10)

These are just a few options, but as you can imagine, the options for how to frame your raised bed are virtually endless. Just be sure to do your research and choose a material you're comfortable with.

4. Raised Bed Garden Soil Lacks Nutrients ⬅

Insufficient nutrients in raised bed soil is probably the most common mistake I see. But when you get it right, the vegetables in your raised beds will thrive.

Many soil combinations will work well with raised beds, but some do not. Potting soil, for example, drains too quickly. Unless your raised bed sits on concrete or rocks (and thus acts more like a container), skip the potting soil. You need more substance than what potting soil can provide.

Potting soil also often lacks nutrients to sustain a raised bed garden all season. Raised beds aren't containers that need constant fertilization; instead, raised beds function best when filled with organic, nutrient-rich soil from the beginning.

compost in raised bed — I top-dress my raised beds with homemade compost, which adds organic matter into the soil.

Another caution: When I conducted a raised bed soil test, I found that plants grown in a raised bed filled only with bagged soil grew much slower than those beds with some amount of organic material mixed in.

What is the best soil for raised beds?

Personally, I've found the best success in my raised beds by using a combination of native soil (or topsoil) and organic material like compost, but depending on what you have available and your budget, you have many options to choose from.

The possible combinations of raised bed soil can get overwhelming, especially if you're on a budget. That's why I put together a free guide to help any gardener — on any budget — discover the ideal soil combination for them. Download the free guide by clicking below.

5. Raised beds are placed too close together.

Working in raised beds can be the joy of any gardener. That's why you want to create the most comfortable working area as possible.

To do this, you want enough room to be able to work between the beds comfortably — two to three feet at least. I made this mistake by only allowing about a foot between my raised beds, and it's always a challenge weeding, planting, and harvesting from those edges.

One thing we all forget is that not all of our plants will stay in the lines of our raised beds. Many plants spill over the edges (like squash and pumpkins), and others just grow so wide they reach over the walkways.

With all that in mind, then, when you place your raised beds on the ground, ensure you can get your garden cart or wheelbarrow in between them. When you have enough space to do that, you can sit a stool beside the beds for a comfortable working area.

garden stool next to raised bed — The garden stool above can be found on Amazon here.

6. Pathways grow up with weeds and grass.

There are few things more frustrating than going out to my garden, planning to enjoy some time working in my raised beds, and discovering the grass has grown up beside them.

Weed and grass overgrowth always has the potential to harbor snakes, and overgrown grass causes my legs to itch. My husband and I both try to keep the area trimmed with a weed eater, but with three acres to maintain, sometimes we can't always keep it tidy.

If you don't want to keep mowing or weed eating the grass and weeds around your raised beds, place a barrier down before the weeds and grass emerge for the season.

Options for the Paths Around Raised Beds

To keep the area around your raised beds tidy and easy to work, you have several good options. Here are just a few:

cardboard boxes
sawdust
pine needles
gravel

Cardboard boxes

Broken down cardboard boxes with a light layer of mulch on top works great! But an even easier method I've begun to use is rolling brown kraft paper between beside my beds and covering with mulch.

Sawdust

My husband is also a hobby woodworker, so I spread sawdust between my beds. I don't recommend sawdust as mulch because it can retard plant growth. But that makes it a great barrier where I don't want nuisance grass and weeds to grow. The key is to lay it on thick — 4-6″ is ideal.

Pine Needles

Another option is pine needles if you happen to have pine trees nearby. Pine needles are my favorite for pathways because they break down more slowly than other materials. Like other organic mulches, lay it on thick, and a layer of cardboard or kraft paper underneath helps as well.

Gravel

Though expensive, a layer of gravel is an option many gardeners choose, especially when their entire raised bed space is in one area. Like the other options, I recommend putting down a barrier first. Without it, grass and weeds will grow between the gravel, and you don't want to have to pluck weeds out of gravel (trust me).

What about landscape fabric?

I know we've all been tempted to use landscape fabric to line our pathways (even as a layer underneath some of the options above), but I don't recommend it. In my experience, weeds will eventually get through anyway. If you do choose a more permanent barrier, I recommend a greenhouse-grade plastic sheeting instead of permeable landscape fabric.

7. Neglecting to Mulch Raised Beds

Mulching your raised beds is just an important as mulching in a ground garden bed, and perhaps even more so.

Though weed pressure is usually less in raised beds, it isn't non-existent. Weed seeds from native soil find light and sprout. Seeds floating in the wind and deposited from birds love the rich soil of raised beds. For these reasons, mulch will dramatically reduce your weeding time.

But more importantly, mulch regulates the soil temperature and retains moisture — both critical needs of raised beds in the hot summer.

One huge advantage of raised beds is how the soil heats up quicker in the spring, allowing for faster planting. But it also heats up as the season goes on. Mulch helps regulate that temperature more than bare soil would.

Mulch also regulates moisture. In wet seasons, it acts like a sponge, absorbing excess rainfall. In dry times, it keeps moisture from evaporating in the heat of the summer. You will find your mulched raised beds much healthier than those without it.

I prefer to mulch with wood chips, and in this post, I talk about the pros and cons of four common types of mulch — all of which I have tried in my raised bed gardens.

Update for 2021: here are 9 organic mulch options you can consider as well.

Hopefully, by avoiding these 7 mistakes, you will be on your way to an enjoyable raised bed gardening experience with abundant harvests!

Do you have anything to add to my list?

More Raised Bed Gardening Resources

How to Troubleshoot and Revive a Raised Garden Bed

If you've had problems with your raised bed soil, this post explains what the problem might be and how to fix it: Problems with Raised Bed Soil

3 Raised Bed Soil Mixes Tested

What is the best soil blend to fill your raised beds with? I put three common raised bed soil mixes to the test, and the results may surprise you.

What do I Put on the Bottom of Raised Beds?

When you're building your raised bed, should you line it with anything? How can you fill it in the least expensive way and still provide fertile soil? This post gives your options: What do I put on the bottom of raised beds?

Raised Bed Garden vs. In Ground Garden

Jill Winger of the Prairie Homestead talks with me about why she changed from an in-ground garden to a raised bed garden to help others decide if it's right for them in this post.

FAQs of Raised Bed Vegetable Gardening

I've received many follow-up questions to this post, and I addressed the most common ones here: Raised Bed Gardening FAQs: 9 Common Questions

Raised Bed Soil Options Free Download

Don't forget to download my free Raised Bed Soil Options for any budget guide below:

Podcast

I discuss each of these seven mistakes in even more detail in this episode of the Beginner's Garden Podcast. Listen here or on your favorite podcasting app.