042-Raised Bed Gardening, Pt. 1: Getting Started

| Podcast, Prepare

Are you building a raised bed garden, or are you looking to improve your raised bed crops? You have come to the right place.

Earlier this year, I invited my email group to send me any questions they would like me to answer on the topic of raised bed gardening. Little did I expect the flood of responses I received.

As a long-time raised bed gardener, I am thrilled to see how many of you are looking to start your raised beds for the very first time – and want to make sure you get off on the right foot. So many of you, too, have experience with raised bed gardening but have questions on how to improve your results. One thing is certain, the information available on the internet regarding materials, methods, risks, etc. – well, let’s just say it’s conflicting at best.

 

Joe Lamp'l raised bed gardens

Joe Lamp’l is enjoying time (and a comfortable raised bed perch) on his GardenFarm.

 

My hope with this raised bed gardening series (and yes, so many questions to answer it’s morphed from one podcast to a series!) is to put that conflicting information, well, to bed for you. It’s my goal to answer all your questions from A to Z, planning to harvest and maintenance, starting with this first episode in this raised bed gardening series.

I invite you to request a copy of my Raised Bed Resource Guide – created out of all the information covered in this series and more. I hope you find it helpful in the coming seasons!  If you would like to join the conversation and contribute to future topics, click the red “Get Free Updates” button at the top of this page.

 

My Raised Bed Gardening Background

You might be feeling intimidated by the idea of building a raised bed garden. Believe me, I understand. I had been gardening all my life when, several years ago, I was selected to host the DIY Network television series, Fresh from the Garden.

 

Joe Lamp'l garden

Joe Lamp’l on the set of Fresh from the Garden in 2005.

 

The focus of the show was backyard food production in raised beds from seed to harvest. I was given free range on design, gardening methods – the whole deal. The only catch? Failure was not an option. Three years, two different locations, 52 episodes, and zero failures later, I attribute my gardening success in large part to all the practices that I will share with you in this series.

About 14 years have passed since Fresh from the Garden. Since then, I’ve designed and overseen many raised bed installations. My Growing a Greener World team and I have traveled all over the country and seen many raised bed garden setups. We’ve seen beds over concrete, lots of community gardens, just about everything. We’ve seen what works and what didn’t.

As part of the Growing a Greener World series, I built my GardenFarm and turned what was five acres of overgrown brush into a large, productive raised bed garden and developing landscape. Six seasons ago, I built the raised beds I now see from my office window. If you’re interested, I invite you to watch the episode on construction and see details of the design instructions I used for building raised beds at my GardenFarm, plus the raised bed diagram.

My garden area is above a septic drainage field. That’s one of the reasons I chose to use a raised bed approach and decided on an 18” height. Six seasons later, the gardens are beautiful, incredibly productive and a little easier to keep in “television-ready” shape.

 

GardenFarm design sketch

Layout sketch of the GardenFarm raised bed set up during early planning.

 

The truth is, I feel that all these years televising my gardening techniques – regardless of the location – my garden has been … everybody’s garden. I’ve just been in charge of building and maintaining it. I’ve made plenty of mistakes and, like you, I never stop learning. I hope this series helps you get a head start.

Why Use Raised Garden Beds?

Raised beds provide you control over the health of the soil in which you are growing your plants. A raised garden bed is simply mounded soil or a contained bed of soil above the surrounding grade. The goal is to create a deep, wide growing area that encourages plant roots to grow down and outward.

 

Native soil in a raised bed garden

Challenging native soil conditions can be overcome through the use of raised bed gardens.

 

Raised beds can put plants at eye level for better observation of pest issues. When the bed is contained in a structure, you are better able to really get in there and work your bed without impacting the overall shape.

I also prefer not having to bend over to maintain the beds. Just that little bit of added convenience makes it easier to work in the garden, even on those days where I might be tempted to just kick back with a cold beverage. Believe me; I have those days too.

Do you live in an area with hardpack dirt, heavy clay (like my red Atlanta clay), fine-grained sand, or maybe your home is surrounded by concrete? Perhaps, you’ve done a soil test and discovered lead or some other contaminants in your native soil?

Raising the garden surface raises your plants above problem soil and can prevent plant roots from reaching those contaminants. By using raised beds, there really aren’t any surface issues that should hold you back from gardening.

When your soil bed is elevated above the surrounding terrain, you control its health and drainage. So, no matter how bad the ground you’re starting with, anyone anywhere can grow a productive raised bed garden.

Frankly, I also just love the look of raised beds. I find their aesthetic value to be a great benefit to my property. Given the options, I can’t imagine not gardening in raised beds.

Do the Benefits of Raised Beds Outweigh the Costs?

There are lots of variables to determine if raised beds are your best garden option. Some great gardeners prefer in-ground gardening. A frequent guest of these podcasts gardens in-ground with mounded beds, and he wouldn’t have it any other way.

 

In-bed garden rows

Mounded, in-bed garden rows thrive at the Lee Reich gardens.

 

Building raised beds can be expensive. It doesn’t need to be, but it can be. In 2009, I was challenged to build an entire garden (including plants) for $25 or less and was fortunate to find 110-year-old barn wood to use for my raised bed structure. It may be worth checking sites like Freecycle.org or Craigslist.org for materials you can repurpose.

Some other potential downsides to raised beds:

  • Their permanence. For most, this is a benefit, but if there’s a possibility you will need to relocate your garden in coming years, a permanent raised bed structure will need to be deconstructed.
  • The raised soil is more exposed to heat and cold than surface soil. If the sidewalls of your bed aren’t very thick, the bordering soil and plants could be impacted by extreme conditions.
  • Raised soil can dry out more quickly than surface soil. During this series, I’ll cover some ways to significantly reduce this downside, but the fact remains.
  • Raised beds require space between the beds for movement, pathways through the garden. If you have a very limited real estate, losing some of it to walking space might be a dealbreaker for you.

Garden Area Planning

There is a myriad of raised bed designs and variations out there. We’ll get to that more next week, but first, consider your space. Bear in mind that these guidelines and principles apply most to an edible garden – growing fruits and vegetables.

You don’t need to have a lot of space to build a raised bed garden. What you do need is a spot that receives full sun for most of the day – at least 6 hours. Those edible plants require lots of sun to mature fully and set fruit for your harvest. So, the sunniest area on your property will be the best garden spot.

If your property is shaded by lots of trees, you may want to consider some selective pruning to allow the sun to reach your garden spot. Be sure to check out the Growing a Greener World blog on that topic and the considerations on this.

 

GardenFarm raised beds at harvest.

The GardenFarm raised beds during harvest time. Their 18″ height makes for easy picking!

 

It’s best if the garden area is relatively level. Many of you are starting with hilly terrain, so I recommend digging into the hill, if possible. Get that area as level as you can before you build.

If your spot isn’t level, and you don’t have the ability to level the ground, just bear in mind that your raised bed surfaces will need to be level once complete. So, starting with an uneven surface will need to be taken into account in your overall design.

Be sure the raised bed area will have easy access to water. Is there a spigot nearby? If not, will it be practical to lay a garden hose from the spigot to the garden area?

It’s easy to forget that a strung-out garden hose will need to be pulled back in regularly (if not daily) to mow, use the hose elsewhere, prevent it from being chewed up by the dog, etc. Water is key to gardening success, so you want to be sure your method will be practical for you.

Consider proximity to your home too. I am a strong advocate for getting out into the garden every day. Take at least a few moments to enjoy the beauty of what you’ve built. Spending some time each day also helps you catch pests and disease in early stages.

Let’s be realistic. If your garden is tucked away on the other end of your yard, and that distance feels like a trek after a long day; you might be inclined to have a seat on your favorite chair instead. And don’t forget, you want those garden edibles to be as close to the kitchen as possible for a quick dinner. Why grow it if you’re too busy to harvest and eat it?

 

Garden location spot

A spot located too far away from your home may be inconvenient and impractical.

 

What are your environmental conditions? Is there anything else which might impact your finished beds? For example, is the selected spot in an area that receives some runoff in heavy rain? Take into consideration how the runoff will impact your bed structure, or incorporate a way (like a French drain) for that runoff to go around the garden area.

If at all possible, don’t site your garden in an area where water tends to pool on your property. Even though the beds will be raised up, pooled water can still wick up into the beds and drown your plants over time.

Will you be battling predators? If you are in a rural area and subject to visitation by frequent furry nibblers, like deer or raccoons; incorporate fence planning into your overall design. Keeping the garden nearer to your home may also help to discourage predators from visiting your garden in the first place. No sense taking the trouble to grow all that produce, only to lose it to your wildlife neighbors.

While you’re planning, know that how you orient your raised beds just doesn’t matter. It won’t matter if their length runs north-to-south or east-to-west. What will matter is the placement of your plants, and I’ll cover that further later in the series.

 

Tall plants in a raised bed garden

Orient your tall plants on the north side of your raised bed gardens. Planting them on the north or west side prevents their shading smaller plants from the sun.

 

Raised Bed Size Considerations

No doubt you’ve already been looking at dozens, if not hundreds, of images of other gardens. So, you know that bed sizes and shapes vary widely. I’ve seen just about everything too – even plants inserted directly into bags of garden soil (not something I recommend). Here are the guidelines I do recommend:

1. Height:  12-18” is ideal, however even as low as 6” can work and be productive. Most feeder roots are in the first 6”, but the deeper the roots, the taller the shoots. Going higher than 18” can potentially cause more structural issues down the road – due to the weight and pressure of all that soil.

Think about what types of crops you want to grow (root vegetables which require more space, herbs which require less, etc.). Think too about the foundation on which you will be building. Will the surface allow the soil to erode out the bottom (go higher), or might it be impacted by the weight of the bed (don’t go too high)?

Provide as much room as possible – and practical – for your plant roots to grow. (If you checked out last week’s podcast, you’d know that an 18” depth is also the perfect seating height.)

 

GardenFarm raised beds

The GardenFarm raised beds, ready for planting.  Built of 6″x6″ cedar beam, each bed is 18″ tall, 3′ or 4′ wide, and 12′ long.

 

2. Width:   Four feet is perfect, but three feet can also work. Four feet allows more flexibility for spacing rows, but more importantly, not building beyond that width will allow you to easily reach the center from either side of the bed. It’s important that you don’t have to step into the bed to weed, plant, etc., as that will compact the soil and affect drainage and overall health.

3. Length:  Whatever fits your needs. You could build 4’x4’ squares. You could build 4’x20’ rows. As long as you stick within a four-foot maximum width, your length is only limited by your space and budget.

4. Shape:  As mentioned, you can build squares, rectangles, T’s, circles, ovals, etc. As long as you can reach all areas of the bed from the edge (staying within that four-foot width), you’re all set.

 

The Complete Guide to Raised Bed Gardening

There was so much raised bed gardening information to cover, that I created a resource guide. Get your copy of the free guide from the Links & Resources section below.

 

Preparing the Garden Bed Area

Maybe you are truly blessed and have bare, level, beautiful earth just waiting for you to come along and plunk some beds down. No? Then, you are like the rest of us who have (or had) to put a little blood, sweat, and tears into claiming our garden spot from turf or shrub or weeds.

If your Space is Currently Lawn:

  • Rent a sod cutter to remove that turf pretty quickly and easily – but be forewarned, this will involve a hit to your budget.
  • Dig up the sod the old-fashioned way. Hello, shovel, my old friend.
  • Smother and compost that high-maintenance grass away. If you are willing to wait a little while, (a few months) this method will provide a nutrient-plentiful base for your garden bed. I have listed the steps for this “no-till method” in my no-till gardening video blog

If your Space is Currently Weed-Infested:

  • Solarize the area. Solarizing will take some time (4-8 weeks), but it is a great way to kill much of the weed growth and seeds for 2-3” below the soil surface. Solarization utilizes trapped moisture and heat and is best done in the hottest months of the summer.
    • To solarize, mow the area as low to the ground as possible, then thoroughly wet it down – really soak it well. Then, cover the area with clear plastic sheeting (clear plastic allows more heat from the sun to penetrate to the soil surface than black or cloudy plastic).
    • The key to solarization is ensuring a tight seal of the plastic edges. Your goal is to trap all that moisture underneath and not provide pockets for heat to escape. It’s best to bury the edges of the plastic under an inch or so of dirt.
    • Periodically, check over the area throughout the summer to be sure the plastic is still well-sealed. If any holes are poked into the plastic at any point during the solarization process, cover them with duct tape.
    • Don’t leave the plastic on for longer than eight weeks, at most. Solarization will kill some of the beneficial microorganisms in your soil, but they will quickly repopulate the area. Remember that this process kills the weeds down to about 3” of soil, so if you dig after solarization, you’ll be bringing those deeper weed seeds back to the surface to cause you more grief.
    • One drawback to solarization is the ultimate disposal of the plastic sheeting. Recycle that plastic, if at all possible.

 

Raised bed plant orientation

How you orient your raised beds isn’t important. What does matter is how you orient your plants.

 

  • Bermuda grass. If you are contending with this adversary, solarization is your best weapon. Bermuda grass is grown intentionally in some areas, but it can also become a very persistent, invasive weed. It grows above ground – using runners – and below ground – using rhizomes.
    • The good news is that solarization can kill Bermuda grass runners as well as some of the rhizomes. However, those rhizomes can run very deep (six inches or more), beyond the reach of the heat of solarization. So while solarization can be effective against Bermuda grass, be prepared to continue this battle for many years to come.
    • Bermuda grass is so persistent; it is the only time I might consider placing a layer of landscape cloth under my raised bed structures. Alternatively, I might lay down several layers of cardboard.
    • I strongly encourage you to build some sort of border around the edge of your bed to prevent Bermuda grass creeping in from the perimeter. Bermuda grass needs plenty of sunlight, so when buried under layers of soil, it’s not as likely to sprout up from underneath. More likely, any sprouts in your garden will be due to seeds blown in.

If your Space is Currently Shrubbed:

  • In some cases, it might be necessary to grind out or dig out a stump or two. Fortunately though, raised beds prevent the necessity to remove most of the stumps and roots left behind. Much of the remaining woody material will be buried in your garden beds and will break down over time, adding a few nutrients to the soil.

You may also opt to till the garden area to tear up existing roots, weeds, etc. and as a means to level the spot. There is some drawback to tilling your soil that I discuss at length in the video blog mentioned earlier.

Tilling can save time and create a surface that is easier to level. Just understand the drawbacks to tilling before you take that step. There are important soil structure elements which can be lost due to tilling. As with all these decisions, once you are educated on the benefits and risks, you can take the direction that best suits you.

 

GardenFarm raised beds

The GardenFarm raised beds provide structure, beauty, and a healthy growing environment.

 

Notice that I did not recommend the use of any topical lawn or weed killing products – either commercial or home-made. If you use a topical product, that product will remain in the soil and will affect your garden bed. It doesn’t take much to kill a season or more of garden crop, so think twice before deciding to take this particular shortcut.

If your Location is Hardscape:

  • I’ve received lots of questions about building raised beds on this. I have seen many home and community gardens built on parking lots, sidewalks, etc. If this is what you have to work with, then go for it! These can be productive garden locations too.

The key to building on hardscape would also be drainage ability. Water should be able to flow out of the bottom of your raised bed onto the concrete. Some people layer cardboard beneath the bed structure to help with water retention, but that cardboard will break down so quickly, it’s not a worthwhile step.

If your only area is gravel, know that gravel might impede drainage. Studies have shown that water doesn’t move as freely from a dense to a less-dense layer. You can check out a video demonstration to get a better understanding. The deeper you build your beds, the less likely this will be a problem, and again if this is the best area you have to work with, don’t let that hold you back!

 

Joe Lamp'l in the GardenFarm

The GardenFarm raised bed height of 18″ allows Joe Lamp’l to better observe growth and early problem warning signs.

 

Which Materials are Safe for Containing your Beds?

Size and shape will likely also be dependent on your materials. More importantly, many of you expressed concerns and had questions about which materials are safe. Here’s where things can really go sideways. There are so much conflicting information and surprisingly few studies on the various materials available for use.

Why do materials matter? First of all, the materials you use will be in close quarters to your food crop. In all likelihood, the roots and foliage will be regularly making contact with your material surface.

Secondly, the soil you place in your bed will need to remain fairly moist, and the exterior surfaces of your bed will be spending a lot of time in the hot sun. Most materials degrade when exposed to constant moisture and sunlight.

I used 16’ lengths of 6”x6” untreated cedar at the GardenFarm but living in the heavily-populated Atlanta area offers me a better supply of wood materials than will be available for many of you.

Regardless, here are pros and cons to the materials you may be considering:

 

Raw Wood:  

The best types of untreated wood are black walnut, cypress, cedar, redwood, oak, black locust, or osage orange. These are known for their rot-resistant properties and last for many years, even under moist conditions.

These woods can be difficult to find available for purchase in some areas. They are also expensive. Untreated pine is a less expensive untreated option, but it will also have a shorter lifespan.

Another consideration:  Aside from pine, these woods are not as sustainable as other materials. Often, these woods are harvested from old-growth forest. If you choose to use one of these woods, check that it is coming from a sustainable source. Look for the Forest Stewardship Council (FSC) certification on any wood you buy. The FSC is an international organization that has developed standards for responsible forest management.

All types untreated wood will need to be replaced at some point. The lifespan of your wood will depend on wood type and your environment. If you live in an arid climate, untreated wood can last for several years. If you live in a hot and muggy area, untreated wood may only see you through a couple of years.

 

Wood raised bed garden structures

A robust raised bed garden form built with wooden structures.

 

Replacing your wood does not signify failure. The untreated wood is decomposing and even adding some nutrients to your garden bed in the process. It’s more a matter of maintenance and realistically assessing what will work best for you and your family.

Wood Stains & Paint:

You may opt to extend the life of your untreated wood by staining or painting it. I recommend using a natural treatment like raw linseed oil or raw tung oil.

It’s important to look for the raw form of these, as those not marked “raw” will likely include other chemicals. The chemicals are added to speed up the oil drying process, so by using the raw versions, allow for additional drying time.

Another thing to bear in mind is that linseed oil is a food source for mildew, so if mildew is a problem in your area, that may not be a good choice for you.

There haven’t been many studies on the impact of using paints or stains for garden bed structure. Paint and stain ingredients vary, and overall, the impact is relatively unknown. But common sense should remind you that these all include chemicals of some nature, and those chemicals may impact your crop.

I recommend against painting the exterior only of your raised bed structure. The wood exposed to the moist soil will wick up moisture, but the exterior paint won’t allow the wood to fully “breathe.” So by painting the exterior only, you will be trapping the moisture inside and shortening the lifespan of your wood.

Treated Wood:  

Treated wood has been infused with chemical elements to preserve the wood. CCA (Chromated Copper Arsenate) wood used to be the most commonly available. The primary concern with treated wood is that those infused elements leach out of the wood. The arsenic in CCA led manufacturers of CCA-treated wood to discontinue its availability for residential applications in 2003.

Although you may find older CCA-treated wood, today’s retail options will more likely be ACQ (Ammoniacal Copper Quat) or MCA (Micronized Copper Azole). They have a higher concentration of copper but don’t have the arsenic.

Leaching occurs at the highest levels under the following conditions:

  • Smaller surfaces – i.e., the ends and – especially, the sawdust
  • More recently treated (although CCA-treated wood is shown to retain uniformly-high levels of CCA)
  • Moist conditions – i.e., after rain or in a muggy environment
  • In unhealthy soil

 

Treated wood raised bed garden structures

Raised bed garden structures being built of treated wood and ready to be filled.

 

So to put this into an interesting perspective, studies exploring the impact of treated wood when used for raised beds have shown that the greatest risk is actually in touching the exterior of the bed. When you (or especially, your kids) sit on or lean on treated wood, your skin or clothing is most likely to absorb the copper or arsenic leaching out of the wood to remain on the surface.

If you currently have beds made of the older CCA-treated wood, don’t be alarmed. If you’re using lots of compost, you should be fine, since plants don’t even take up arsenic unless the soil is deficient in phosphorus. And that’s likely not the case since phosphorus tends to be immobile and ongoing amendments of compost just add to the overall volume.

In other words, really healthy soil with lots of organic matter does not take up arsenic by plant roots. Yet the more acidic or alkaline your soil, the more likelihood of those elements being taken up by your plants. So, just another reason for getting a soil test to get your soil closer to a neutral pH (6.5-7.0 – also the ideal range for vegetable growth). Ditto for soil with a low amount of organic matter, so make sure your soil analysis tests for organic matter percentage as well.

As for the newer ACQ and MCA treated wood (which have higher copper levels), plants in your food garden won’t be able to tolerate high levels of copper, and studies show that healthy soil also prevents uptake of copper.

Even if copper levels are high and being taken up, the plants will die before you ever have a chance to think about eating them. At any rate, that would be a good indicator of a potential problem – in which case you might want to think about having your soil tested for metal concentrations.

While we’re on the subject, root vegetables are at greatest risk of being impacted by leaching, as most metals (when taken up) remain in plant roots. Studies further show that those root vegetables are impacted most on their surface. So by thoroughly washing all the impacted soil off and peeling the skin off your potatoes, beets, etc.; you will be eliminating potential contamination.

Your tomatoes and your eggplant could absorb copper or arsenic into their roots, but it is generally not shown to affect the fruit. Leafy greens are an exception and can take up arsenic in their leaves.

In short:  Keep your soil near neutral and add lots of compost (more on both of these later), thoroughly wash off the soil and peel the skin from your root vegetables, and avoid contact with the exterior surface of the treated wood. As an extra precaution, grow leafy greens and root vegetables more toward the center of your bed (12” from the perimeter if possible), furthest from the treated wood.

A final note: When building treated wood beds, make your cuts somewhere that allows you to contain the sawdust. Wear a dust mask and gloves, and remove and dispose of the sawdust promptly. Don’t add it to your compost.

Cinder or Concrete Blocks:

The truth is, these days the terms are used interchangeably. If your “cinder” blocks are decades old, they may actually be cinder blocks, but only concrete blocks have been in production for the past 50+ years.

What are your concrete blocks made from? That depends somewhat on your area, but there are consistencies. Virtually all concrete blocks are made of what’s called Portland cement as well as aggregate, like sand or gravel.

One of the ingredients of Portland cement is fly ash (ranging from 15% to 25%). It’s used to make concrete blocks lighter yet stronger. Fly ash is a fine powder byproduct of coal burning, so In other words, it’s a petroleum byproduct.

And here’s the real rub: fly ash contains various amounts of toxic metals; including arsenic, lead, and mercury. So, yes, those metals are in the concrete blocks that line your vegetable garden too.

 

Concrete block raised garden bed frame

A concrete block raised garden bed under construction. (photo: Joan DiSante)

 

While that might sound scary, the risk of those metals becoming available in the soil only happens if part of the concrete block is pulverized. Then, it’s a matter of several factors that determine the potential risk to what you are growing.

First, the proximity of plant roots to the damaged area. Next, soils higher in organic matter are always beneficial but especially in this case, because they help chemically bind the metals – making them unavailable for absorption into the plant. Just as with CCA-treated wood, root crops and leafy greens are most susceptible when exposed to higher concentrations.

So, how much fly ash is absorbed by soil held within a concrete block structure? Well, if the block is intact, little to none. But not much research has been done on this specific subject.

If you have beds made from concrete blocks, just avoid anything that would cause them to break to the point that the dust from pulverized pieces can come in contact with plant roots.

And if you really want to “do something,” seal the interior lining with a polymer paint (the most practical option), or line the interior side with PE plastic. It’s up to you to decide if it’s really worth the trouble.

If building raised beds over a concrete surface, the same risks and preventions would apply.

 

Raised beds on concrete

A raised bed garden built on a concrete area.

 

The bottom line:  It’s not a huge risk, and there are many other ways you are likely taking unintended and harmful materials into your body, far beyond the risk posed by these blocks. That’s my opinion, but I do encourage you to do your own research on this if you’d like to learn more. There is so much information out there on the subject, and it will quickly take you in many directions. So, just be mindful of the reliability of the sources of these articles.

Composite Wood:

Composite wood is made of recycled materials and can last for years. Some composite material, when used in long side walls can buckle a bit. Here again, there hasn’t been much research on the use of composite wood in proximity to edibles.

Are there any chemicals or elements released by the composite material? It appears to be a benign product for garden use, but there isn’t much information out there to make a solid determination.

Railroad Ties:  

Railroad ties are made with creosote, an oil distilled from coal tar. Creosote is used as a wood preservative for industrial use and is the black, oily stuff you see oozing from the sides of the ties.

The heft of railroad ties has made them a popular choice for raised beds and garden retaining walls. While there have been few studies on the impact of using them to contain edible plants, I’ll take the advice provided directly from the EPA on creosote:

“…Creosote is not approved to treat wood for residential use, including landscaping timbers or garden borders…. Creosote is a possible human carcinogen and has no registered residential use.”

Galvanized Metal:

There’s little scientific information available examining the effect of galvanized metal in the use of raised beds. What I can tell you is that the galvanization process typically involves dipping the metal in molten zinc or zinc-based coating.

While dangerous if consumed in large quantities, zinc is a micronutrient that plants and humans actually need in small quantities. If too much zinc were leached into the soil, it would probably reflect in dying plants, before it would ever pose a health risk.

Also, galvanized metal has been used to hold or transport water for humans and livestock for many years. All that to say: I can’t guarantee there’s not a negative health impact, but the risk is certainly low.

 

Galvanized tub raised bed garden

A galvanized tub raised bed garden provides a home for herbs and vegetables. (photo: Dennis Huckabay)

 

One thing you should bear in mind, however, is heat and drainage. Livestock troughs are a popular option, but it’s critical to provide lots of drainage holes in the bottom of the trough. That moisture will need a place to escape, so you don’t inadvertently drown your plant roots.

Whether you use metal sheeting or a trough, that metal will absorb and reflect heat from the sun – more than other materials. As a result, your soil will tend to dry out more quickly, and foliage in the line of that reflective power might suffer. The soil nearest to the sun-facing metal will also warm up more than the rest of the bed.

It might be wise to plant those tender vegetables – like lettuce – toward the center of the bed where soil temperature will remain most constant.

Tires:  

Just don’t. Don’t do it. If you must do it, do it only for a season or two at most. Tires are a petroleum-based product. Their rubber degrades in the heat and moisture, and the chemicals incorporate into your soil. They may be convenient or look kitschy and fun. It may keep a tire out of the landfill, sure. But there are more drawbacks to using tires than there are benefits.

There’s a reason that most landfills prohibit tires. If garbage shouldn’t be subjected to decomposing tire rubber, neither should your family’s food.

 

Tire planter

Most landfills prohibit tires. If garbage shouldn’t be subjected to decomposing tire rubber, neither should your family’s food.

 

Pre-Made Kits:

It doesn’t get much easier than one of the many raised bed kits available for purchase today. These can be used with composite wood and can be cut to varying lengths. Some can be expensive, and the material with which they are made can vary widely. I recently built raised beds on an episode of Growing a Greener Worldso check that out.

Liners:  

If you use any of the above materials with the potential of leaching, you might be inclined to line the bed with plastic. Yes, this will provide a barrier between the bed material and your soil. But don’t lose sight of the plastic material itself.

There are so many plastics out there, and they are of widely-diverse safety grades. If you use plastic, look for food-grade polyethylene. This is considered one of the most food-safe plastics. Line only the outer perimeter of the bed – not the bottom surface. Don’t block drainage with plastic.

With all of these products, I recommend you do your own research to feel comfortable in your choice. There are many reputable and not-so-reputable resources out there, so always be mindful of your information resource.

 

Raised garden bed kit

Raised bed kits, similar to the parts being used here, make it easy to build a bed at any size and in any location.  Seen here are widely-available builder blocks with composite wood, which can be cut to any size.

 

Be sure to watch for next week’s podcast when I’ll continue the raised bed journey, discussing two of the raised bed topics that generated the most questions – structure material and soil. There is a lot to cover there, so I encourage you to listen in and read up.

Speaking of listening in, if you haven’t already done so, I recommend listening to this podcast recording (linked at the top of the page).  I include a few anecdotes and other tidbits that I think you will find enlightening and entertaining.

Links & Resources

Request a copy of The Complete Guide to Raised Bed Gardening

Podcast Episode 006: Weedless Gardening with Lee Reich

Podcast Episode 041: Small Space Garden Design   joegardener Blog: No-Till Gardening: If You Love Your Soil, Ditch the Tiller

joegardenerTV: How to Get the Best Drainage for Your Container – Why What You’ve Been Taught Is All Wrong

Growing a Greener World

GGW Blog: Limbing up Trees   

GGW Blog: Salvaging 110-year old wood – My Quest for a Twenty-five Dollar Organic Victory Garden

GGW: GardenFarm Raised Bed Instructions

GGW: GardenFarm Raised Bed Garden Diagram

GGW Episode 406: Setting Up a Garden

GGW: Episode 804  Gardening for Butterflies & Other Beneficial Insects

EPA: Creosote

PennState Extension: Environmental Soil Issues: Garden Use of Treated

Craigslist.org

Freecycle.org

Milorganite® – Our podcast episode sponsor and Brand Partner of joegardener.com

 

 

About Joe Lamp’l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Growing a Greener World®, a national green-living lifestyle series on PBS currently in production of its ninth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm, just north of Atlanta, GA.

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