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Raised Bed Gardening

by Stephanie Suesan Smith on August 28, 2010

Do you have rotten soil that won’t grow anything?  Or are you just starting out and have nothing but sod?  If you are dreading digging that out so you have a garden, you can build a raised bed instead.

Raised beds have many advantages over planting things in regular beds.  Some of them are:

  • You add soil so it can be good, well drained soil instead of clay gumbo
  • Raised beds warm faster in the spring
  • Weeds can be better controlled because the soil is free of weed seed at planting
  • Higher beds means easier access — no more gardening on hands and knees
  • Raised beds drain better

Initially, building a raised bed is a lot of work. It pays off later.  If you want to build a raised bed, there are several things to consider.  The first is what type of plants you are growing.  Vegetables and many flowers require at least six hours of sun a day.  Building a bed in the shade to grown them is a waste of time and money because without that sun, those plants won’t grow.  Now, there are plants that like partial shade.  They may not do well in a bed in the full sun.  So deciding what you want to grow and picking an appropriate site is important.

Another part of site selection is drainage.  If you put your bed where it will always be wet, such as a seep or low spot that is always full of water, your plants will drown.  You need to pick a spot that does not have standing water or a tendency to flood with every rain.  A raised bed improves drainage, but it can only do so much.

Now you are ready to design the bed.  Raised beds do not have to be square or rectangular.  They can be any shape you want.  Keep in mind, though, that you want to be able to reach every plant in the bed without actually having to climb into the bed.  Stepping on the soil compacts it, which is a bad thing.  Compacted soil drains poorly and is hard for roots to penetrate.  It also has less air in it, so the plant doesn’t get as much as easily.  For these reasons, most people build beds that are no more than four feet across.  They may be long, but relatively narrow.

Ask ten gardeners what material to use to edge their raised bed and you are likely to get ten different answers and at least one fist fight among the respondents.  Traditionally, people used Wolmanized® lumber, old railroad ties, landscape timbers, or deck planks.  The problem with using these is they are all treated with arsenic or creosote to prevent rotting.  Sounds good, but studies show those chemicals leach into the soil of the raised bed.  Plants take them up and your nice organic vegetables suddenly are not so healthy.  So it is recommended you do not use treated wood for the edges of your bed.

So what do you use?  Metal edging will work, as will wood that has not been treated.  However, metal edging will rust out over time and wood will rot out.  This means you will need to replace either one as they wear out.  Bricks or cinder blocks will work, as will stone, if you have them.  They now make composite planks that are made of outdoor grade plastic.  They are more expensive than wood but do not rot, rust, or leach things into your soil.  Pick your material and decide how much you need to build your bed.

The bed only needs to be 8-12 inches deep for flowers and 12-18 inches deep for vegetables.  Some people build the beds about two feet high so they can sit on a stool and work them.  If someone in a wheelchair will be working on the beds, they will need to be higher — high enough so the person can comfortably reach the plants in the center of the bed.

Next you need to see to the irrigation.  How will you water the plants in your bed?  Drip irrigation is the most water efficient.  Setting up the irrigation is beyond the scope of this post, but you need to decide what you will use and install the parts of it that go below the soil now, while you are building the sides of the bed.

Now you get to the actual building phase.  Mow down the vegetation in the area you want to build the bed.  Put newspapers or some other barrier that will let water out but keep weeds from growing into your soil.  Newspaper works well because it will decompose slowly and by the time it is gone, the weeds and grass will be dead.

Place the edging material where you want the bed and anchor it into the ground to hold it.  Install your irrigation system, or at least the parts that go underground.  Then add soil.

Of course, adding soil is not as easy as just dumping it in.  First, you have to decide what kind of soil you want.  For vegetables, a 50/50 mix of compost and topsoil works well.  If you are growing an acid loving plant, you want peat moss and soil.  So again, you have to plan what you want to grow to know what kind of soil to get.

After the soil is dumped in, you will need to smooth it around and get it level, then put the rest of the irrigation system in place.  Now the bed is ready for use.  It is important to put mulch around the plants when they are big enough — the usual three inches is good.  Then enjoy your new raised bed and the plants in it.

Gardenbookfrontcoverthumbnail For more help gardening, buy my book, Preparing A Vegetable Garden From The Ground Up
Available in print or ebook from Amazon.com or other retailers, this book walks you from choosing the site of your garden all the way through what to do after the harvest. Buy a copy for yourself or a friend today! 


{ 2 comments… read them below or add one }

Ken Panitt August 30, 2010 at 7:26 am

Our brand of preserved wood (Wolmanized®) has been used for decades on farms and in
gardens for tomato stakes, vineyard trellises, mushroom trays, and raised
beds. These thousands of applications, plus many laboratory studies, enable
us to say with confidence that there is no cause for concern from harmful
uptake of preservative ingredients into fruits or vegetables. This was true
with our past preservatives; today’s copper azole preservative is considered
even less of a risk. It contains two active ingredients: copper, often used
as a soil amendment, and a carbon-based fungicide approved for direct
application on food crops and as a post-harvest wash of fruit.

On our website appears a building plan for a raised bed structure
(http://www.archchemicals.com/Fed/WOLW/Docs/BuildingPlans/Backyard_projects_–_Raised_Bed_1-08.pdf).
There is a note which you might want to review regarding use of a liner.
Elevated copper levels are very unlikely to present a health risk, but, if
you want to maintain the original composition of the planting soil, you can
consider a liner.

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Stephanie Suesan Smith August 30, 2010 at 8:56 am

Thank you for your comment. There is still considerable debate about using treated lumber. If enough chemicals leach into the soil to make a liner advisable, then that is too much for many of my readers.

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