10 Myths About Raised Beds

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Robert Pavlis

Raised beds can be a great way to garden but don’t believe everything you read about them. They aren’t magical! They are a box, that holds soil or a soil-like material. Plants get water and nutrients from them and sun from the sky, just like plants growing in the ground.

If you understand these myths you will grow great food.

rabbit looking at a raised bed

What is a Raised Bed?

The term raised bed is a bit confusing. If you add a few inches of soil to a garden bed so that it is raised a few inches above ground level, it is a raised bed. When most people talk about raised beds for vegetable growing, they mean a bed that has been raised with walls surrounding the soil, sometimes called a garden box or framed bed.

In this post I’ll use the term raised bed to mean a bed that has walls.

Myth #1: It’s Easy to Grow Vegetables in a Raised Bed

If you have a lot of experience growing vegetables it is easy to grow them in any soil. Raising up the level of soil does not make it any easier, except that it takes a bit less bending. Plants grow equally well at ground level and at higher levels, and at ground level they need to be watered less.

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If you are not familiar with growing vegetables, raised beds won’t really help you. The things you have to learn to become a good gardener have very little to do with the height of the soil.

Starting with a bed of really good soil can help a first time gardener, but it’s almost as easy at ground level.

Myth #2: Different Soil in Every Bed

It is certainly true that raised beds make it easier to have gardens containing different soil. But is that really a good idea? Are there clear guidelines for the “best” soil for each type of vegetable?

As a new gardener, it is difficult enough to learn the basics of growing vegetables. Complicating that with a variety of different soils, each of which takes different cultural techniques, is not a good idea. Learning how to use one type of soil is difficult enough, learning how to use several is too confusing.

Which soil is the best? Try and find authoritative sites that tell you which soil to use for each crop. You won’t find any. For one reason, it is too complex and secondly, most vegetables grow just fine in the same soil mix. If you start with a good soil as described in Soil for Raised Beds – Which One is Best?, you can grow 95% of the vegetables.

Myth #3: Raised Beds Have Fewer Weeds

The claim here is that since the soil level in beds is higher, weeds have a harder time growing up through the bed. People who believe this also put things in the bottom of the bed, such as cardboard or landscape fabric to stop weed growth. Neither should be used in the bottom of a bed, in part because they don’t stop weeds.

The reality is that most weeds are the result of germinating seeds either from in the soil used to fill the bed or from the ones that land on the bed as wind blows them around. Weeds coming from below ground are not a common source.

Microbe Science for Gardeners Book, by Robert Pavlis

The exception are a few very nasty weeds such a Canada thistle, field bindweed and quack grass, which travel long distances underground. If you have these weeds, higher beds with or without landscape fabric in the bottom, won’t stop them.

YouTube video

Myth #4: Never Use Ground Soil

People have been conditioned to believe that their natural ground soil is toxic, does not contain any microbial life and won’t grow plants. That is rarely the case.

Some soil is toxic. If your house was built on old industrial land it may have a problem. A older house that used lead-based paint, might have higher lead levels in the soil around the house. If you think there might be a problem have the soil tested. However, the majority of garden soil is not toxic.

What about soil life? Builders do remove the top soil before construction and that is where a lot of microbes live. They then bring a small amount back to lay sod. So your soil may not have a lot of microbes, but even bad soil has millions of microbes in every speck of soil. As you garden and improve the soil, the microbes will quickly grow and fill the soil.

Natural soil may have high levels of clay, or high levels of sand. Neither of these are perfect for plant growth, but some simple amending with compost quickly corrects these problems. And it is much easier and less expensive than hauling in new soil for a raised bed.

The natural soil in 90% of home gardens will allow you to grow great plants.

Myth #5: Beds Get Overheated in Hot Climates

Raised beds heat up faster in spring and the soil may be a bit hotter than soil in the ground, but the difference is very small.

Beds with metal walls will feel hot on the outside since the galvanized metal absorbs a lot of heat, but heat won’t be transmitted into the soil. In one report the majority of the soil in a metal bed was 89°F (32°C) and only right next to the metal did the soil reach 97°F (36°C).

I have also seen the claim that black grow bags get too hot, but I measured the temperature in some bags and it was barely above ambient temperature.

Myth #6: Raised Beds Use More Water

This may or may not be a myth depending on the material you put in the bed. If the bed is filled mostly with soilless mix, or compost, it will dry out much faster than soil at ground level. If the bed is filled with mostly real soil, especially if it contains a lot of clay, the bed won’t dry out much faster than at ground level.

Mulch is also key here. Use lots of mulch and the bed won’t dry out nearly so fast.

Myth #7: You Can’t Add Too Much Compost

This is a complete myth. Too much compost can lead to high levels of phosphorus which results in soil that is too toxic for plants. And once levels are too high it is difficult to reduce it.

Myth #8: Pressure Treated Wood is Toxic

Prior to 2004 the chemicals used to make pressure treated lumber included a process call CCA which contained arsenic. Small amounts of arsenic can leach from this wood and be absorbed by plants. For this reason old CCA pressure treated lumber is not recommended for raised beds.

Almost all of the pressure treated lumber available today in North America and Europe uses a process called ACQ which does not contain arsenic or other heavy metals, but it does contain copper. ACQ treated wood is considered safe for use in the garden.

If you are planning simple, low beds, I would stick to untreated wood, knowing that it needs to be replaced more frequently. However, if you are building high beds and using a substantial amount of wood – I would use ACQ treated wood.

Also see: Best Building Material for Raised Garden Beds

Myth #9: Galvanized Steel is Toxic

Corrugated metal is becoming more popular for raised beds because it lasts longer. It is more expensive and I think it’s ugly. It is a good choice for high beds, but these should only be used if the gardener has a disability and can’t use lower beds.

Corrugated metal is usually made from galvanized steel, which is coated with a zinc alloy. The zinc can leach out into the soil, but the levels are considered to be very small. Both plants and animals require some zinc in their diet so there is no health concern.

3 foot high metal container growing vegetables
Galvanized metal raised bed, source: Christa

Myth #10: Raised Beds Have Fewer Pests and Diseases

I have news for you. Neither pests nor diseases know that you are gardening in raised beds. They are after the plants and as long as you grow plants, you will have the same pests and diseases as someone growing in the ground with one exception. Raised beds may have fewer slugs especially if the bed is up on legs.

It is even possible that you have more pests. Studies have shown that higher levels of nitrogen produce plants that are more attractive to pests, and many raised gardens are made with high levels of nutrients.

One of my readers did comment that a raised bed keeps her dog out of the garden. Fair enough. A higher bed will also keep rabbits out, but squirrels and birds will still get in.

Soil Calculator

Raised beds need more soil than you think. I have developed a simple online soil calculator to help you determine how much soil or mulch you need for the garden.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

7 thoughts on “10 Myths About Raised Beds”

  1. It’s interesting what people believe. If they were to look logically at these myths they would know what you wrote is true before reading it. That said, part of my garden is raised, 10 x 20x 16”. My soil is some what rocky and my neighbors have gophers. So I put gopher wire on the bottom and added dirt and raised bed soil , about 50/50 mix. and it took a lot. It still gets bugs and plenty of weeds but no gophers. None of the weeds come from the bottom but from the wind and birds dropping seeds. The roots are too short to come from the bottom.

    Reply
    • I think I updated the post to mention slugs – that is a valid point.

      Increased aeration depends on what you use to fill it.

      Reply
  2. I grow flowers in raised beds one meter wide with grass paths between. I lay a 2 inch layer of strulch on top to help keep the moisture in and discourage annual weeds. I kneel on the paths to tend the beds. I think if there were not well defined wooden edges to beds it would be difficult to keep the strulch confined to the bed. ( or will I know learn that using strulch for moisture and weed control is a myth?

    On the beds with no strulch because I am rotating the plants or sowing seeds I think it would also be difficult to keep the soil in the bed and off the grass.

    Other than that all your points about raised bed make complete sense.

    Reply
  3. I concer! one question I have is if using a tri-mix from Greeley (top soil, manure, wood chip) in a wooden box, would I need to use something along the lines of liquid seaweed fertilizer later in summer for a winter crop of garlic?

    Reply
    • I would not use a mix like top soil, manure, wood chip. The wood chips will use nitrogen as they degrade and plant roots may struggle.

      Reply
  4. Agree with pretty much everything you wrote. I don’t known why there is this belief particularly among new gardeners, that raised beds are a panacea. When I had raised beds with wooden sides I found that I had a harder time keeping the soil moist because it runs down the sides and flows away rather than penetration the soil in the bed in spite of using soaker hoses to irrigate. I suppose a very slow drip irrigation could overcome that. In a regular garden bed, the water tends to pool and slowly absorb into the subsoil.

    Today I have done away with the wooden sides and have slightly elevated beds relative to the permanent paths. I find I need to water far less frequently. And BTW, I once tried Hügelkultur which was by far and away the hardest to prevent from drying out. Put an end to that before very long.

    Reply

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