The Dirt on Raised Garden Beds: Mining the Urban Waste Stream for Building Materials

Many recycled and repurposed materials can be sourced from the urban waste stream and used to create planting containers and raised garden beds. Which materials are safe and non-toxic? Which materials are the most durable? I have unpacked the options with this investigation on the pros and cons of a variety of potential materials.

Labyrinth garden bed

Here is a set of criteria that can be used as a guide. First, lets consider the toxicity of different available building materials on a scale of 1 to 4, with 1 being completely non toxic and 4 being relatively toxic. Which end of the toxicity scale you choose depends on whether you are growing food crops or ornamentals? This is an important determining factor for obvious reasons.

The second criteria is longevity. This I rate from A to C, where A is for materials that are short lived and C for materials that can last over 20 years. I have combined these two criteria in the table below. They will help you determine the most appropriate building materials for your garden project. I have populated this table with different materials that I have used over two decades, with a description of their merits.

Toxicity and longevity table for repurposed and recycled building materials.

1) non-toxic 2) semi non-toxic 3) relatively toxic 4) toxic
A) 1 season straw bale old guitar
B) 10 years old tea pot  old saxophone old tuba wine bottles wine barrel drift wood logs salvaged lumber redwood old shoes,  old boots old doors  old boat old dresser
C) 20 + years horse trough  reclaimed metal old toilets old bathtub urbanite brick stone Recycled plastic lumber  copper pressure treated lumber Arsenic pressure treated wood  vinyl old tires

You may see things on the table that make you wonder, “What? planting container?” Don’t worry I’m just pushing the envelope on possibilities. Our cities’ rubbish bins are teaming with items and materials that can be used to contain plants. So consider this a fishing license for the urban waste stream. One man’s trash is another man’s planter.

For instance, my old food blender recently gave up the ghost. Instead of just tossing it in the trash I filled the blender “container” with soil and planted it with succulents.

Blender planter

Of course I have inserted into the table many of the conventional building materials used for raised garden beds. Here they are with a description of their merits. In another instance someone had a “Jimi Hendrix moment” with their guitar and threw away the smashed instrument. I pulled it out of the trash, put soil in it and planted it with succulents. People are delighted when they see it, especially when they hear the story behind it. As you can see I cast a wide net in the search for building materials for the garden. While I’m on the subject…I’ve been on the lookout for a tuba that maybe was run over by a school bus. I want that tuba for a planter and I am going to call it garden art.

I) + A) Straw bales

Straw bales are inexpensive and if you are resourceful even free.  Tomato starts can be planted right in the bale just by replacing a handful of straw with a pocketful of soil. As the photo shows, straw bales can be configured as raised garden beds, filled with soil and planted. Of course the bales will only last for a season and then become compost. A short-term, cheap, non-toxic and fun way to build a temporary garden bed and soil at the same time.

Straw bale planter
Raised bed made from straw bales
Growing tomatoes in straw bales.

1) + B) Old tea pot, old saxophone, old tuba, wine bottles, wine barrels, driftwood, logs, salvaged lumber, redwood. The teapot, saxophone and tuba used as planters are all examples of playful, whimsical garden art. Metal, ceramic or porcelain items will all be long lasting, non-toxic plant containers, (Hint: dril a hole at the bottom for drainage.) Wine bottles planted upside-down and side-by-side can make an attractive garden border. An up cycled creative re-invention of a common household item. Wine barrels have been used as planting containers ever since vintners started casting them off. They last up to 10 years and are pleasing to look at, brimming with herbs or flowers.

Wine bottles for edge
Wine barrel planter

Driftwood and logs are often available for free, and can make fine raised garden beds that last 10 years or more. These materials can be simply laid in place without much more to do.

Salvaged and redwood lumber: With a little surfing on the internet at FreeCycle or CraigsList, can located. New redwood and other hardwood lumber that has been sustainably harvested can be found if you trust the Forest Stewardship Councils’ “FSC” label. It is nice to think that sustainably harvested lumber is available, I have found small scale local mills to be trustworthy. Redwood can last ten years with soil up against it. With a little carpentry these lumbers make fine garden beds.

Salvaged lumber
Sustainably harvested redwood

1) + C) Horse trough, reclaimed metal, old toilets, old bathtubs, urbanite, brick, stone

For horse trough, reclaimed metal, old toilets and old bathtubs: The size of troughs and bathtubs make them viable as raised garden beds. Reclaimed metal and old toilets require some artistic license but can be turned into long-term plant containers.

Re-purposed horse trough
Salvaged iron metal

Toilet planter

Bathtub bed

1) + C) Urbanite, Brick & Stone

Urbanite is the funny made-up non-brand name for repurposed concrete pieces. A surprisingly available, long-lasting, non-toxic building material sourced from the urban waste stream. Earns high marks for environmental friendliness. Brick is laborsome to manufacture; however when installed correctly it gets high marks for longevity and being non-toxic, especially when used without mortar. It’s fairly easy to repurpose again and again. Often found available used on Craigslist.Stone, (flagstone, granite, field stone, river cobble, pea gravel, etc.) is without question the quintessential non-toxic building material. However, questions do arise regarding its source. It is a mined product that carries a heavy environmental cost but makes up for it in longevity, especially if it is salvaged and re-used. Unparalleled aesthetics in the landscape earn it high marks.

Raised Garden beds using 'urbanite'.
Sonoma field stone

2)+ A) Old guitar

Okay, okay…short term garden art. Mine is about four years old and it’s falling apart. But it sure has a good story behind it.

Blog author Ken Foster and his 'Jimi Hendrix moment'
A crafty guitar

2) + B)  Old boots and Old shoes, These bootswere made for walking…but now they’re retired and growing strawberries. Good thing there is a hole at the bottom for drainage.

Growing strawberries for Nancy Sinatra...These boots where made...
   
What are these planters doing in the trash?
Comes with drainage.

2)+ C) Recycled plastic lumber, I like that there is plastic . I have seen raised garden beds made from old doors. Old doors, as well as old boats and old dressers they may have paint and/or glues to wonder about. Still, I’ve dreamed about getting an old (small size) fishing boat, filling it with soil and growing food in it.

Open door policy in the garden

4)+ C) Pressure-treated wood, copper pressure-treated wood, vinyl, old tires

Fun but toxic.

Now we’re getting toxic. In the old days as late as the nineteen nineties, pressure treated lumber was impregnated with arsenic. Then children started showing up with cancer from playing on structures made with it. That product was taken off the market and while copper tressure-treated wood is much better, I still don’t like growing food in it. The jury is out on using it for garden beds. Virgin vinyl is an extremely toxic product and I don’t like the idea of growing food in it. Then there’s old tires. Recycling this huge waste problem in the garden? Tires are chock full of heavy metals like lead and cadmium and simply are not appropriate to grow food in.

Now that you have learned a little about the dirt on raised garden beds, build some and put the dirt in them where it belongs. -Ken Foster

Urbanite: The Upside of Upcycling

I don’t usually get all gushy about cement. As a self-professed “softscaper” and plant lover I don’t have much use for the stuff. I opt for plantscapes and permeable surfaces over concrete. Then urbanite comes along and I’m just about ready to write a love sonnet.

“Urbanite” is the affectionate name for re-purposed concrete pieces. It’s a funny made-up-name for a common solution to a waste problem. I would even argue that the concept of urbanite could be raised to the level of metaphor because of its transformative role in restoring impervious, compacted, lifeless areas. This common resource is surprisingly available and is often used by creative landscape designers who seek building materials sourced from the urban waste stream. In ecological landscaping, urbanite is a material of choice and it has been a darling of the Permaculture movement for good reason.

 

Surprisingly available resource

Urbanite is easy to like for these reasons:

  • It is a free material. However, it does take time to locate, and labor to load and transport.
  • It is upcycled, which is the process of converting waste materials or useless products into materials or products with new value.
  • There is no mining involved, unlike much of the raw material found in landscape supply yards which are mined in quarries. Flagstone and mossy field stone, for example. Yup, there’s a hole where that bolder once was.
  • It is versatile. It can be used for a variety of hardscape purposes like patios, walkways, stairs, retaining walls, raised garden beds – and even herb spirals.
  • It lasts. Isn’t that the definition of concrete?

The term “Cradle to Cradle” applies nicely to urbanite because it has been repurposed and can be repurposed ad infinitum. The upside of upcycling urbanite is that the embodied energy of the original concrete is captured. Embodied energy is a term to describe all of the energy that goes into the production of a product. It includes the manufacture, acquisition of natural resources, mining, transport, office administration and all other aspects of producing a product.  Reuse of building materials commonly saves about 95% of the embodied energy that would otherwise be wasted.

Before
During installation

 

After

Its usability is urbanites primary benefit because the manufacturing process of concrete has one of the heaviest carbon footprints of all building materials. The high temperature needed for cement manufacturing makes it an energy-intensive process. The average energy input required to make one ton of cement is 4.7 million BTUs—the equivalent of burning about 418 pounds of coal. For ready-mix cement it takes from 1,075 to 4,085 BTUs per pound. A BTU, short for British Thermal Unit, is a basic measure of thermal (heat) energy and is one way to measure embodied energy. Comparatively, it takes 123 BTUs per pound to produce adobe brick.

One of the tasks of ecological landscaping is to reduce overall inputs by sourcing materials with low BTUs per pound or by finding ways to capture embodied energy by upcycling, enter urbanite. Often in the process of redesigning a landscape existing concrete walkways and patios can be carefully deconstructed and turned into urbanite for the regenerated landscape. A brilliant way of capturing embodied energy right on site.

Honor the hard work that goes into urbanite installation.

While the “embodied energy” assessment is an important piece in knowing the environmental impact of a product like cement, true full impact accounting takes it a step further by assessing all impacts on people and planet. In business this is referred to as “triple bottom line” accounting which includes “profit and loss” analysis in all the three realms of economy, ecology and equity. This includes considering the impacts of things like:  Strip Mining, Clear Cutting, CO2 Production, Air Pollution, Fossil Fuel Use, Energy Consumption, Resource Depletion, Polluted Runoff, Disposal Problems, Worker Health Problems, Support of Irresponsible Companies, Damage to Cultures and the Effect on Communities. This is a stunning list of impacts that to a surprising degree come with the production of cement, the “feedstock” of urbanite. While each of these impacts can be debated, what is clear is that urbanite is a creative way to turn a nasty problem into an elegant solution.

 

Raised Garden beds using 'urbanite'.

The installation of urbanite takes some forethought. Like with other hardscape materials (such as flagstone), it is important to give urbanite a sturdy foundation. For instance, in preparation for installing walkways, patios or retaining walls, it is best to excavate 5 or 6 inches below grade and then install drainage rock and tamp well. The result is both good drainage and a solid foundation. This is important for liability reasons and because there are few things as disconcerting as a shaky retaining wall or shifting stepping stones.

Careful 'dry stacking'

Because concrete pieces are often chunky careful stacking is best done using guidelines from the mason trade. Dry-stacking, which means the process of laying pieces together without mortar keeps the material expense low. For a safe, tight result stack level using a hammer and chisel to correct uneven surfaces as you go always using protective eye wear. Because urbanite is heavy stuff get plenty of help when lifting and use your knees! Finally, a new stain is a good finishing touch. This can be achieved using non-toxic stains like iron sulphate (which is also is a fertilizer) or a product called SoyCrete for that new finished look. With all these environmentally and socially friendly reasons, when it is designed well and installed correctly we are very happy to give it the affectionate moniker of “urbanite”.   – Ken Foster

Old patio cut up with a concrete saw and re-installed.