Raised Beds

Raised Beds

Why Grow in Raised Beds?

​I love my raised beds and usually add 1 to 2 more every year to my garden. There are several advantages to using raised beds to grow vegetables.

1. Ergonomics. First, it is ergonomically easier for many people to reach raised beds because you have a shorter distance to bend to work in your garden. I also bought a gardening stool to sit next to my raised beds to plant and weed. More recently we have been converting our older raised beds to 6x6s which means I can sit on the side of the raised bed which is even easier on my body than using the stool.
2. Drainage. Raised beds drain much better than in-ground gardens. This is usually an advantage as we get plenty of rain most summers. Last year we had an unusual drought, so I ensured everything was mulched well and irrigated frequently with a soaker hose on timers. This year however, (2024) we have had massive amounts of rain (about 20 inches of rain in both May and June) and many of the plants in my in-ground garden have succumbed to root rot, wilt, and other diseases. I lost about half my tomatoes and most of my brassicas that were planted in the ground. My potatoes look pitiful and many of my squash also wilted and died. I have had some problems in my raised beds, mostly fungal disease on my melons and 2 peppers wilted (out of about 50), but significantly fewer problems in comparison to my in-ground garden. This year I have not even bothered to mulch most beds as I am trying to promote drying out rather than moisture retention.
3. Better Soil. You can control the soil you put in the raised beds, so you are not fighting the naturally occurring soil in your area. We have pretty good soil but also some drainage issues in our main in-ground garden. However, many people live where the soil is predominantly sand or clay, neither of which is great for a garden. My plants in raised beds always grow better than the ones in the ground and because the soil health is better, I can also grow more per square foot than in a traditional in-ground garden. You also do not need to worry about walking paths in your raised beds which provides more room for plants.

Raised beds made out of untreated 2x10s with 2x4s for support (not placed in their final position, at least 3 feet between raised beds is recommended). A second layer of 2x10s can be added to increase depth. These raised beds have lasted 7 years in central Wisconsin, even with untreated wood.

Materials

​What materials to build your raised beds with is a hotly debated topic. I prefer untreated wood, although I would be comfortable using treated wood today as copper is used as a preservative rather than arsenic. A study by Oregon State University (4) has found that only one inch of soil along the edge of the bed shows increases in copper levels, and that increase was small (20 ppm over untreated raised beds). We started with untreated lumber as it was cheaper than treated and even using untreated 2x10 boards our raised beds have lasted about 7 years. We built our first raised beds in 2017 and only this year (2024) have we started to replace some of the sides. We bought an Alaskan sawmill this spring and own a red pine plantation that needs thinning, so my husband has been milling 6x6s to build new raised beds and replace our older raised beds. The big advantage of 6x6s is that you can more comfortably sit on the edge of the bed to plant or weed.

The gold standard for raised beds is cedar wood. I would love raised beds made out of cedar 6x6s but cedar wood is unfortunately extremely expensive. If you are only going to build one or two raised beds you could consider cedar depending on your budget. However, I have 19 raised beds and the cost of cedar is unrealistic. There are also other rot-resistant wood types, such as redwood, but they can be hard to source and expensive.
Metal-raised beds, usually steel galvanized with zinc to prevent rusting, are becoming more popular. Although zinc can be toxic in large amounts it seems unlikely that enough would leach into a raised bed to cause toxicity issues. We also use galvanized food and water containers for our chickens and ducks and galvanized water tanks for livestock have been used for a long time. Therefore, I feel a galvanized metal raised bed is unlikely to cause health issues. Furthermore, I have heard good things about some of the metal raised bed kits (such as Epic Gardening Birdies Metal Raised Garden Beds[6]) you can buy regarding longevity and ease of construction, but I have no experience with them myself. If you decide to buy a galvanized livestock tank to use as a raised bed instead of a raised bed kit, just be sure to add drainage holes and ensure it is tall enough to accommodate the roots of your plants.

Concrete (cinder) blocks are often used because they are easily available, relatively cheap, and heavy so no extra supports are needed. I would not use concrete blocks because, in addition to cement, sand, and gravel they also contain fly ash which is a byproduct of burning coal. However, this will likely only leach into the soil in large amounts if the integrity of the block is compromised. If you use concrete blocks, in good condition, this may be an acceptable choice for a raised bed. You can also choose to line your concrete blocks with a food-safe plastic liner, however, many people do not like growing food in plastic, even food-safe plastic.
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Materials I do not recommend are railroad ties, due to the creosote used as a preservative which is also a carcinogen. I also see old tires being used locally as raised beds, but this is not recommended since tires are made of petroleum-based products. Rubber degrades with exposure to UV light from the sun which will then leach petroleum chemicals into your soil.

New raised beds made in 2024 of 6x6s we milled on our property from red pine trees. Ignore the unhealthy melon plants, massive amounts of rain made this the worst gardening year I have ever experienced.

Size

​A typical raised bed size is often 4x8 feet. The first raised beds we ever built were five feet wide. This was too wide to easily reach the center of the bed for planting and weeding. I suggest limiting your raised beds to no more than four feet across, but three feet is also acceptable, particularly if you are on the short side. The distance in length does not matter although I suspect eight feet is often used because wood is readily available in eight-foot sections, and it is easier to transport. There is no reason however that you cannot make longer raised beds, you would just need support along the way. Many people also get creative and make raised beds in different shapes to make meandering pathways between them. I am unfortunately not that creative and line mine up in two rows with each bed running north-south.

My older raised beds were made using 2x10s so they were roughly 9.25 inches high or, if we added two layers, for example, to grow asparagus with deep roots, were 18.5 inches high. These were a great height but made it difficult to sit on the edge given the sides were only 1.5 inches wide. Our new raised beds made with 6x6s are currently only one layer high, so 6 inches (these are actually 6 inches high since we milled them ourselves, if you buy 6x6s in a lumber yard they will likely be 5.5” unless you can find rough sawn wood). We plan to slowly add more layers of 6x6s as we have the time to mill more logs. Ideally, a raised bed is 12-18 inches tall, but I found having the wider 6x6s raised beds easier to work with than the taller 2-inch-wide boards so am willing to sacrifice height temporarily until we mill more 6x6s. Even a 6-inch raised bed provides advantages to growing directly in the ground.
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As far as spacing is concerned, I like 3-4 feet between each raised bed. I found that 2 feet is too small to easily work in between raised beds.

We drilled holes and used large 12 inch spikes to hold together our raised beds made with 6x6s.

Buy or Build?

​Whether you buy or build your raised beds comes down to two different factors: budget and DIY ability. We chose to build our raised beds because I wanted quite a few of them which made buying them too expensive, and my husband and I are reasonably handy. We already had the tools needed (saws, drills, etc.) to build wooden raised beds. If you do not already have tools available weigh the cost of buying a raised bed kit with the cost of buying or renting tools plus lumber to build your own. Many hardware stores will also cut lumber to size for you so that could eliminate the need to buy a saw.
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When we built our raised beds with 2x10s we used screws to hold the boards together with a 2x4 at the corners. When we used 6x6s we pre-drilled holes through the 6x6s and then pounded a long spike through to hold them in place. In general, screws are preferable to nails because if you make a mistake, you can easily remove the screw. One thing we did not add to our raised beds is hardware cloth lining the bottom. This is used to prevent rodents from burrowing underneath and eating the roots. This has not been a problem for us but if you have high rodent pressure in your area I would recommend it.

A raised bed made out of 2x10s with a second layer added for extra height. We used this raised bed to grow asparagus.

Soil

When starting a raised bed from scratch I like to combine peat moss (make sure you buy the sustainable Canadian peat moss), topsoil or garden soil (about 50%), compost/composted manure, and sometimes a little sand. We usually get our topsoil/garden soil delivered as it is cheaper than bags if you need large amounts. Our compost is either our own (kitchen scraps mixed with used pine shavings from our chickens and ducks that have been composted sufficiently to reduce any pathogen load) or compost in bags we get from our local home improvement store. Sometimes peat moss is not recommended because it can cause your bed to dry out too much. I add no more than half a bag to my 4x8 foot raised beds and have not had a problem. After a raised bed is established, I usually add an inch or two of compost each year to maintain the fertility of the soil. I also grow many plants in pots and when I need to refresh the soil in my pots, I often dump the leftover potting soil into my raised beds (assuming no diseases were present). Potting soil usually has good drainage so this can also increase the health of your raised bed soil. The cost of filling a raised bed can be as expensive or more expensive than the cost of a raised bed itself, so be sure to add up the total cost before you build too many raised beds you cannot afford to fill. This is why we have slowly added 1 or 2 raised beds per year rather than making them all at once.

Conclusion

​I love raised bed gardening and firmly believe the advantages outweigh the time and cost required to build or buy them. The vegetables in my raised beds routinely outperform my other vegetables in both output and health. If you wish to learn more about raised bed gardening, I encourage you to read or listen to Joe Gardener’s blog/podcast (links below) which is very comprehensive, and check out the other resources provided.

References and Resources

1. Joe Gardener. 042-Raised Bed Gardening, Pt.1: Getting Started. March 8, 2018. https://joegardener.com/podcast/raised-bed-gardening-pt-1/
2. Joe Gardener. 043-Raised Bed Gardening, Pt. 2: Perfect Soil Recipe. March 15, 2018. https://joegardener.com/podcast/raised-bed-gardening-pt-2/
3. Joe Gardener. 044-Raised Bed Gardening, Pt. 3. Animal Control & More. March 22, 2018. https://joegardener.com/podcast/raised-bed-gardening-pt-3-animal-control-more/
4. Pressure-treated wood for raised bed construction in the Willamette Valley. https://extension.oregonstate.edu/gardening/soil-compost/pressure-treated-wood-raised-bed-construction-willamette-valley
5. The Safety of Materials Used for Building Raised Beds. https://extension.umd.edu/resource/safety-materials-used-building-raised-beds/
6. Epic Gardening Birdies Metal Raised Garden Beds. https://shop.epicgardening.com/collections/birdies-original