A Practical Guide To Raised Beds
Updated: Apr 27, 2022
Traditional rows are what are used on large farms. Plants are spaced wide enough apart within each row to allow for full growth of the plant. Rows are spaced much further apart to allow for foot access and for farm machinery. I’m sure if you grew up with a vegetable garden in your urban backyard, this is how your parents did it too. It's just how it was always done. The problem is, traditional rows are a really inefficient use of space. We don’t really need huge access paths when we don’t need to drive a combine down our little veggie garden, do we? Yes, this method can work, but there is a better way.
What Is a Raised Bed?
Raised beds condense side by side rows together. Instead of having a walking path between each row, we have a walking path between every 4-8 rows. We make these integrated rows, or beds, only wide enough that we can reach all the way across them (or reach to the middle, if they are accessible from both sides). Voila! You now have dedicated, permanent raised beds. This is beneficial for many reasons.
Why Raised Beds Are Better
More Growing Space
We end up with more total square feet of growing space because we have eliminated a large proportion of the pathways. More growing room means more veggies!
Because we can reach into every inch of our raised beds, we never need to walk on them. This means less compaction, which is good news for our soil. We also don't have to till the soil every year because it is not packed down and hard. Save that rototiller for creating new beds only! When we compact our soils by walking on them or till them with machines, we can seriously harm the soils we are trying to nurture. What's so bad about compaction and tilling? Here's what:
Both tilling and compaction kills many beneficial organisms. These are our earthworms, beetles, other insects, fungi, bacteria and numerous micro-organisms that help our plants by breaking down organic material and making micro nutrients available to our plants. A healthy soil food web means healthy soil and healthy plants.
Tilling brings weed seeds that were previously buried and dormant up to the surface. Here they are then exposed to light, water and air. The result? Weed seed germination and lots more weeds.
Tilling significantly reduces soil nutrients. Much of the carbon sequestered in the soil is lost and nitrogen is quickly consumed.
Compaction and tilling damages the friability and texture of our soil. In healthy soil, minerals, organic material and particles of various sizes, work together to create spaces within the soil. These spaces allow for good drainage (our roots need to breathe), moisture retention (so water is available to roots as well) and aeration (so our roots have room to grow).
Are you convinced yet? Raised beds result in less compaction and less work for us because it eliminates tilling. That's a good deal for us and our plants!
Customize Your Soil
Not all of us are gifted with great soil in our yards. Many of us in newer neighborhoods here in Calgary have barely 2" of cheap topsoil thrown on hard packed clay. Builders go for aesthetics and cost, not good potential gardening. Those in older neighborhoods may be dealing with contaminants and years of compaction. By utilizing raised beds, we can provide clean, well drained, healthy soil to our plants. We can also adjust the pH or organic matter content to suit specific plants much more easily in raised beds than in traditional in-ground gardens. Think acidic soil for blueberries. Soil full of organic material, beneficial organisms and lots of nutrients will also help rehabilitate the soils beneath them.
Eliminating tilling isn't the only reason we get fewer weeds in our raised beds. By not walking within the beds, we are not carrying in weeds seeds and roots bits on our shoes. This doesn't sound like a bid deal, but it does make a big difference!
The soil in our raised beds warms up faster in the spring and dries out faster too. Our choice of bed frame material can enhance this effect even more. Rock and concrete will radiate warmth into the soil well after the sun has gone down. This means we can start planting a little bit earlier in the year, allowing us more time for ripening and enjoying our harvests sooner. Our soils in raised beds also stay warm longer into the fall, once again with frame materials able to increase this effect. All in all, we end up with a longer growing season, and we need every day of growing we can get!
Less Resources Needed
We no longer have to maintain (weed, water, fertilize, dig, etc) the pathways, only the growing areas. Less work for us and less resources used. You save money, water and stress on your back.
You can build your beds to match any specific needs you may have. Bad back? Raise the beds up higher so you don't need to bend over to plant, harvest and care for your plants. Shorter arms? Make your beds a bit narrower to suit you. Limited mobility? Make paths extra wide so that it is easier to maneuver around them. Do what works best for you.
A two foot wide bed is easily reached from one side and a four foot wide bed is easily reached from 2 sides. Of course you can adjust this if you need. If you are going to be square foot gardening, where exact measurements are required, be sure to measure inside dimensions of the beds, not outside measurements (see the article on intensive gardening here for more info). Beds can be any length, although wood beds will need additional bracing if overly long to prevent bowing. Your raised beds can be any depth at all, but keep in mind that the deeper they are, the more fill you will need.
There are endless possibilities when it comes to material for building your raised beds. Actually, you don't even need to use a frame at all. If cost is an issue, or you are unsure how permanent your beds will be, just mounding up the soil up works too. Just ensure that when you are done earth scaping, the soil in your beds are flat and level. This will help prevent erosion during rain events and irrigation.
Wood is one of the most popular options for building, and one of the cheaper ones too. You will need a minimum size of 2x6" boards. You could go wider for deeper beds, but don't go thinner than 2" so that you don't get massive warping. Pressure treated wood can be an issue if you are growing edibles (chemicals can leach into the soil), but the newer brown pressure treatment is supposed to be much more environmentally friendly. Honestly, I have used good old untreated SPF for all my beds and here in Calgary they have lasted 10+ years and are still going strong. This will be a cost vs. work decision for you. Creosote soaked old railroad ties are a big no-no.
Use corner brackets for extra strength (the ones used for decks are perfect) and use all-weather wood screws (such as deck screws), not nails, if you want the beds to last. Alternatively, you can pound a 2x2 stake into the inside of each corner and screw the boards into that. The downside of this is you lose some planting room to the stake. Yes, it's a small amount but every bit counts! If you are joining long boards together end to end, a metal tie plate or mending plate (also used for decks) will make the joint strong. Plywood over the joint can also work. Try to ensure that any end-to-end joints are staggered (not at the same points on either side of the beds). If beds are especially long, think about adding an additional cross brace connecting either side of the bed. A 2x4 positioned on its narrow side (so it interferes with plants the least amount) and screwed into each long side may be necessary. Pre-drilling all your holes will help prevent wood from splitting.
Plastic-wood composite boards can be used instead of traditional wood for longer lasting beds. Keep in mind, they will be more expensive and many brands tend to warp and twist more than regular wood, especially in the heat. Other options for bed frame material are bricks, pavers or concrete blocks. These will last much longer, especially if rebar or mortar is used to connect them, but have very high price tags. If the raised bed border is wide enough and sturdy enough, it can make a great spot to sit as well. Galvanized steel is another unique idea for bed borders, but probably the most expensive of all the options. Don't forget about recycled materials. Using what you already have or what you can scrounge is the most cost effective and the best for the environment. Think wood logs, old pallets, larger rocks, woven willow branches or hay bales. Get creative and don't forget about aesthetics. Just because our raised beds are practical, doesn't mean they can't also be beautiful.
If rodents are an issue in your area, it is good idea to lay down chicken wire or metal mesh in the bottom of your beds. Galvanized hardware cloth with 1/2" or 1" squares works well. Extend the mesh up the insides of your frame and attach with large staples. This will prevent gophers, voles and other root eaters from feasting on your veggies from below.
If you have very contaminated soils, putting plywood or another solid surface in the bottom of your beds can be an option. Keep in mind this turns them into containers, not raised beds. Containers do not overwinter perennials here in Calgary so this would only be useful for annual plants. The depth of your beds would also be very important if you have installed a bottom. You will need a minimum of 12" for growing and a minimum of 24" if you are thinking about root crops. Because your soil will not be accumulating minerals and nutrients from the soil and rock below, you will also need a constant schedule of fertilization, just as you would with any other container.
And please, do not put landscape fabric in the bottom of your beds. It is not necessary to block weeds (they arrive by seed and land on the top of the soil) and will only end up a huge mess in the end. Read about the evils of landscape fabric here (link coming soon).
There are a few options when it comes to filling up those beds and getting them ready to plant. If you have some time before you want to plant, lasagna gardening is an option. This involves putting down thick layers of organic material (straw, mulch, dried leaves, grass, etc.), manure, compost and cardboard. You then soak everything thoroughly and let time decompose the lot. If you start out by laying down large branches and logs in the bottom of the bed, you will have what is called hugelkulture beds, which require even more soaking to start off with. Both lasagna gardening and hugelkulture beds are great if you have an abundance of materials available to you and if you are building and filling beds the year before you will be planting. This gives them the remainder of the year plus the winter to break down.
If you want to get planting right now, start off with soil that has plenty of organic material and beneficial organisms. As I mentioned above, you need a bare minimum of 12" of soil depth, 24" for root vegetables, but deeper is better. If you are putting the bed over your existing soil, break it up a bit. This will help roots grow even deeper into your native soil and help beneficial organisms and nutrients move more easily between the two environments. You also don't need to fill your beds right up to the top of the frames. Actually, it is better to have the soil recessed 4-6", allowing the bed frame to act as a windbreak and helping to increase soil temperatures more quickly each morning.
Here is a good mix to start with for raised beds:
50% good quality topsoil, 30% homemade or good quality compost 20% filler (dried leaves, worm castings, aged manure, peat, fill dirt, etc)
Fertilizer is a huge topic in the gardening world and big business for garden centers and fertilizer companies. Here's the deal. Compost is all you need. Add 1-2" of it to your beds every year, preferably in the fall so that it has all winter to work its way in. You don't need to till it under, just lay it on top. Compost has everything you need:
macro-nutrients (nitrogen, phosphorous and potassium),
micro-nutrients (all the other important minerals that are needed in smaller quantities),
beneficial fungi, worms, insects and bacteria (if it is good compost)
it will help break up clay soil (which we have a lot of here in Calgary) and it will help out sandy soil
it will improve the friability and texture of your soil,
it will also help to stabilize your soil's pH (especially our very alkaline soil here in Calgary).
When you add compost you are doing far better things for your garden than just adding fertilizer, which usually consists of just the three macro-nutrients. And it is all natural. Don't let people trying to sell you fertilizer convince you differently. Okay, I will now jump off my soapbox.
Between The Beds
So now that we have talked about what to make our raised beds with and what to put in them, we need to address what goes around them. These are our access paths. Before you decide how wide they need to be, think about what you will be using them for. If you only need to walk down them, 2 feet will suffice. If you need to push a wheelbarrow down them or kneel while planting seeds and weeding, then 3-4 feet is a better idea. Remember that wheelbarrows and wagons don't have the best turn radius, and err on the side off too wide rather than too narrow.
We need to consider price for our path material, but also how easy they are to maintain, how good they look and how easy they are to drive a wheelbarrow down. Large rocks are not so good for wheelbarrows. Lesson learned. I now have wood mulch between my raised beds and I love it. I top it up every 5 years or so with free mulch from arborists in my area. The best part is I can wander along and pick out weeds, small rocks or other debris from my raised beds and just drop them in my mulched paths. Super convenient. Options for paths include:
Grass: maintenance involved and frequent use may wear it down, lovely to walk on
Mulch: low maintenance, may need topping up every few years, houses beneficial organisms, may not be good for bare feet
Perennial ground cover: takes a while to get established, can be very walkable and attract pollinators depending on the species chosen, good looking
Rock: hard to walk on and wheelbarrow over, expensive, will eventually get weeds in it, even if you put landscape fabric underneath (see my rant on landscape fabric here)
Pavers or bricks: lowest maintenance, most expensive, very good looking.
Raised Bed Additions
The last thing to consider with raised beds
is the accessories. This includes plant supports and any row covers we may need for protection against insects or frost. Having standardized bed widths makes installing and using these accessories much easier. Many gardening structures are made especially with 4 foot wide beds in mind.
I find the setup pictured at right works best for me. It is a 2 foot piece of rebar pounded into the earth beside a raised bed. The rebar is permanently situated on the outside of the bed frame and becomes an attachment point for row cover hoops, trellises and other plant supports. It is on the outside so we don't lose any room inside the raised bed that could be used for plants. I then slide any attachments over the rebar. I have used cut hula hoops spanning from one side of the bed to the other. These are perfect for draping old bedsheets (for when we get frost) or insect cloth over. I have also used PVC piping (ABS or PEX piping would work as well) with right angle joints for more permanent frames over my strawberry beds to hold bird netting in place. Those birds love my strawberries! This specific photo shows the rebar that will hold metal electrical conduit pipe, which is bit stronger and therefore more appropriate my 8 foot tall supports used to string train my tomatoes (see my plant supports article here for details - link coming soon).
In the photo above I have the extra tall support behind with newly planted tomatoes and strings from the base of the plants to the horizontal piece. In the front bed is a shorter version with netting tied between the supports for beans to climb. Both of these supports are made from metal electrical conduit and fittings and anchored over rebar as shown above. Also note the insect cloth over hoops in the middle. Using metal frames that slide over permanent rebar posts allows me to move the supports from bed to bed each year. This makes crop rotation much easier (learn more about crop rotation in my article on Crop Planning: Part 1). My tomato and bean supports can move along with the plants as their planting location changes.
There are myriads of possibilities when it comes to raised bed accessories. So head to the hardware store and start imagining the possibilities.
Phew, that's a lot to consider! Raised beds can be a long lasting and productive part of your landscape for years to come. So put some thought into how to make them work the best for you and look fantastic at the same time! If you have any questions or need more details, contact me! The link is below.
Yummy gardening everyone!
References and Further Information
"The Joe Gardener Show" https://joegardener.com/ A plethora of gardening online courses, videos, podcasts and articles.
Bartholemew, Mel "All New Square Foot Gardening" 1981, Cool Springs Press, Franklin, Tennessee, USA
Watts, Melanie J. "Growing Food in a Short Season" 2014, Douglas and McIntyre Ltd., Madeira Park, BC, Canada
Lee Valley Tools (https://www.leevalley.com/en-ca) for row covers, trellises and every garden tool you can think of.
Veseys Seeds (https://www.veseys.com/ca/) for row covers, trellises, amendments, seeds and lots of tools.