Raised garden bed with Lettuce and broccoli

How To Avoid 5 Common Mistakes And Build The Best Raised Garden Beds

Want to know how to build the best raised beds for your vegetables? Learn how to avoid these 5 mistakes that gardeners are making with raised garden beds.

Thinking about building your own raised garden beds? But worried you’re going to waste time and money if you don’t build them right or fill them with the wrong soil?

Or maybe you’ve built some in the past that just didn’t work out.

Raised garden beds are preferable to simply creating a bed in the ground for the following reasons:

  • better drainage
  • easier access
  • control over quality of the soil
  • warms up faster
  • more aesthetically pleasing if made from the right materials

So what do you have to keep in mind when designing and building a raised garden bed or two?

Are there some mistakes you might make that you will regret later?

Keep reading to learn how avoid those mistakes in the first place.

Using pressure-treated lumber

landscape ties

This is a bit of a controversial topic. The manufacturers of pressure-treated (PT) lumber want you to think that today’s PT lumber is safe, even for raised garden beds that grow edibles. They say that the chemicals in the lumber are locked in and don’t leach out even in very wet soil.

However do you really want to take a chance with your family’s health? It just takes one family member who has a repressed immune system or a young child to fall sick. There are so many other alternatives that in my opinion using PT lumber for raised garden beds that will grow food crops just isn’t worth the risk.

I would still use PT lumber for fence posts and other posts that will be set in concrete in the ground. And PT lumber should be used for deck framing as it is stronger than cedar or redwood. However you need to make sure that any edible plants are planted at least a few feet away.

So what are the alternatives?

I wrote an article on The Best Lumber To Use In The Garden which lists all of the pros and cons of common lumber you could use outdoors. Then you can chose the lumber that meets your needs and budget.

Building with concrete

concrete wall with ivy

Concrete is relatively permanent. That’s why some gardeners think that it is the perfect material to use for a raised garden bed. After all there is nothing to rot away so these beds will last a long time.

However that reason alone makes this not a good idea. While you hope that your raised beds will never need to be moved or changed, there is a possibility that your needs change and you do decide to move a bed or change the orientation. 

With concrete you are going to have to break it up with a jackhammer and sledgehammer. Back-breaking work! And what do you do with the broken up concrete? It is not that easy to recycle or reuse.

Modular raised garden beds made out of wood, bricks, cinder blocks or stone are easier to break up and you can use the materials again for new raised beds in a different location or shape. Or reuse them in another project in your garden.

Concrete also can leach a lot of lime into the ground. If you have plants that prefer acidic soil, they will not do very well.

Concrete beds also require proper reinforcing and are susceptible to cracking, especially in winter if any water gets into even a hairline crack. When that water freezes it can create a larger crack. Not easy to fix either once that has happened.

In my opinion concrete also is not aesthetically pleasing unless you face it with some other material such as stucco or veneer brick or stain it (and the stains do contain chemicals that you may not want to have close to edibles).

Making them too wide

You need to be able to reach all areas of your raised bed without having to step onto the soil. Stepping onto the soil will compact it and then you have drainage and other issues.

A standard maximum width is usually 4 feet (1.2m) assuming you can reach in from both sides of the bed. If the bed is against a fence and you only have access to one side, make the maximum 2-3 feet (0.5-1m). 

Use multiple beds if you need more space, separated by a pathway. The pathway size will depend whether or not you need to roll a wheelbarrow or other equipment through it. I used 3 foot (1m) pathways (see photo) but you could go down to 2 feet (0.5m) if it is only for access by one person for planting, weeding and harvesting.

Download the Free Family Raised Bed Garden Guide

Discover how you can easily setup a vegetable garden, so that you to grow food for your family at home

Exposing end grain and not capping it

Top of wood post

I see designs all the time that call for using 2×2, 2×4 or 4×4 posts in the corners of raised beds to tie together the sides of the beds. This is a strong construction method at least when newly constructed.

However one flaw with this is that the exposed ends of the posts will absorb water from rain and irrigation. Over time these saturated posts will start to deteriorate and rot.

To solve this problem you need to cap the posts or change the construction to avoid using posts. Capping the posts with a decorative post cap like what is used on fence posts works but may look a bit odd.

If you do decide to go this route here are some post caps you can consider:

Simple caps from the same wood used to construct the beds. Here are some cedar ones you can find on Amazon if you are having problems sourcing them from a local lumber yard or big box store.

Woodway Flat Bottom 4×4 Post Cap – Premium Cedar Wood Fence Post Cap, Newel Post Top 4 x 4, Fits Up to 3.5 x 3.5 Inch Post, 1 PC

Or if you want a fancier, longer-lasting option click below for a durable, attractive option that Amazon sells:

Nuvo Iron Decorative Pyramid Aluminium Post Cap for 3.5″ x 3.5″ Posts – Black

To add some light to the top of your posts, especially if you use your garden at nighttime, you can also add solar-powered lighted post caps such as these ones available on Amazon:

Solar Post Cap Lights Outdoor- 4 Pack LED Fence Post Lights for 4 x 4 Wooden Posts Warm White Waterproof for Deck, Patio or Garden Decoration (Black)

The better way is to avoid the posts in the first place and tie the corners together with metal brackets or more sturdy construction.

My raised garden bed design uses some 2×4 vertical braces to strengthen the corners but then uses 1×4 trim on top to cap the ends of the 2x4s.

This construction design is used in both of my eBooks, which are available for purchase in my shop.

For more info on capping end grain including an interesting video demonstration, I’ve written an article that covers the 7 Essential Tips For Building Long-lasting Structures

Using the wrong soil

hand holding brown soil

When I had my raised beds filled in the spring of 2017, I had to purchase some soil. I skimped and saved about $30 by not going with a higher quality soil.

I regret that now as the soil I got had a bit too much sand in it and ended up turning to concrete if not protected by mulch.

To solve this problem I have been adding compost and covering the soil with mulch in order to try and build up the soil health. Planting cover crops will also hopefully build up the soil. But I have to live with it until the soil has had a chance to improve.

I’ve also heard horror stories of gardeners using what is sometimes dubbed “killer compost” or “killer manure”. Persistent herbicides are often still used  on hay fields to kill broadleaf weeds. Horses and other livestock eat the hay but the persistent herbicide does not break down during the digestive process. The resulting manure is laced with this herbicide that is still very active.

If this manure is used in the garden (even if composted first) it will stunt your plants or worst case kill your plants. The only way to get rid of it is to either remove the contaminated soil or try to amend the soil and keep turning it to expose it to sun and oxygen as Joe Lamp’l in the linked story above had to do.

So what is the secret formula then for raised garden beds?

  • build them from non-PT wood (cedar or redwood are best), brick, stone or blocks
  • build them no larger than 4 feet (1.25m) wide if you can access both sides, 2-3 feet wide if you can only access one side
  • make sure all end grain is capped
  • obtain top quality soil or have enough of your own compost on hand to amend poorer quality soil

Also check out this video on my YouTube channel for more info on how to build the best raised garden beds:

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  1. Great post Marc. There’s plenty of food for thought for me here as I contemplate building some new beds, both outside and one in my tunnelhouse.
    Is your new e-book about this out yet?

    1. Thanks Lyn, great to hear this information is useful to you.

      The eBook showing how to build a planter box (which can be adapted to raised beds as well) should be available in the next two weeks.

  2. Everyone has their own opinions about this controversial topic. And it’s ultimately a decision you have to make, after factoring in all the pros and cons. Just like with using any synthetic chemical fertilizers, pesticides or herbicides.

    However I am not willing to take a chance with my family’s health. So I rather pay a bit more and buy non-treated lumber that will last almost as long.

  3. Thank you for your article. My word of advice is if your are building bed for a child or if like me you are a short little lady. Keep your beds at 2-3 feet. When I originally made my beds they were 4 ft wide and I had a lot of difficulty reaching into middle. I redid them. Most are 3 ft wide and like you my one one the fence side is just 2ft in width

    1. I agree. Definitely adjust beds based on your height and the height of the beds. That’s why for my daughter I built the 2’x3’ bed. It also backs against the greenhouse, so only really two sides are accessible. If you are building the beds against a fence or house, definitely go with 2’.

      One advantage with a raised bed though is that you could take a board wider than the bed and lay it across the top and then kneel on that to reach less accessible areas.

  4. Thank you for this article! My husband and I just built three beds, 4×12 by 22 inches high. I appreciate the information on capping the tops of the 4×4 posts, we had not heard that before, but will do it. We are retired and hoping the beds will make gardening in the years ahead easier. But it sure is a lot of work building and filling them! We were able to find a source for a mix of compost/top soil to fill them with. It is lovely soil and we can’t wait to start planting.

    1. Thanks for your comments, Rose. Yes, that end grain really needs to be capped. Such a common mistake I see.

      I remember filling our beds! It was a ton of work. Glad to hear you got some great soil and good luck with your garden this year!

  5. I solved some of these problems by building the raised beds out of inexpensive plastic lumber with galvanized corner brackets. They are 2 “boards” high with a top piece to make a seat. I plan on adding a 3rd “board” and hoping that will make them too high for the rabbits. There are 3 beds 4’x8′. I still have to wean myself from planting in rows.

    1. That sounds like a good alternative to using wood. We have rabbits too sometimes in the garden, but so far I haven’t needed to do anything to keep them out.

      I still plant in rows in my raised beds, but have also started to plant more in blocks, especially using the Seeding Square.

  6. Great article and thank you. I’ve just bought a house with a nice big garden in the Channel Islands, and I will build some raised beds. A primary reason for me was that I hoped this might give me some way to control the snails which otherwise destroy my plants – unless I use pellets, which I am keen not to do. No mention of this in the article: is that because this is a given benefit and there are no downsides or potential flaws or…? Cheers

    1. Thanks for the question. Yes, one of the benefits of raised beds is that you can protect your crops better from some pests. With slugs and snails, you can use copper tape or mesh on the edges of the tops of the beds to try and stop them from crawling over. But you do have to make sure there are no gaps in the copper or holes in the sides of your bed. And make sure the slugs and snails haven’t already taken residence in the bed!

      I do have an article planned in the future to cover various pest repellants and deterrents as well as organic control measures.

  7. I’m not entirely sure where my boyfriend and I went wrong with our raised bed garden. We built it last year out of old pallets. We planted only 2 plants just to see if it would work. They sprouted, but never grew any vegetables. This year we bought soil that said it’s made for raised bed gardens and the new vegetables sprouted and grew a little, but each plant only had one vegetable each. And neither the pepper nor the tomato grew big. Before I read your article, I figured that maybe the wood was wrong, or perhaps it didn’t have enough drainage. It does still perplex me, but I’ll read all the articles you have about gardening and perhaps I can come up with an explanation and have a better plan for next year.

    1. Old pallet wood can contain chemicals used to preserve the wood, especially against insect damage. Drainage could also be a problem, depending on what surface you placed the raised bed on. And picking the right site with enough sunlight is key too, especially for tomatoes and peppers. But there are other variables as well. I’ll send you a followup email to see if we can determine what happened and how you can have better success next year!

  8. My wife and I are in our 70’s and enjoy growing peppers for our cowboy candy in raised beds built on racks that we can place three plastic cement mixing trays in each rack. I drill five small holes in each tub so the water doesn’t stand around the roots too long. We don’t have to bend over or get on our knees to work in our garden. We have been doing this several years and enjoy a plentiful harvest each year. You can use pressure treated lumber to build the racks because it doesn’t affect the plants.

  9. That’s a great idea Ben! I’ve been meaning to do a post for a while on accessible gardening and was thinking of a similar idea for people that can’t easily bend or kneel down or are in a wheelchair. Great idea with the cement mixing trays! Or you could also use plastic storage bins, like the ones you store Christmas decorations or extra clothes in.

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