Guest Contributor: Cassey Anderson, Horticulture Agent, Colorado State University Extension
There are two overall groups of gardeners who emerge once autumn and early winter rolls around. First are those who want to spend some time not thinking about their gardens and relish some quiet and rest, and those who bemoan the lack of garden in their life and want to plan and execute the following year. For those of you who fit into the second category this article may be right up your alley. If you fit into the former group, you can ignore this right now and dive back in once motivation has struck once again next season.
Vegetable gardening can be accomplished in so many ways; in containers, in soil, in water, and in raised beds. Raised beds are often what someone pondering a garden may think of: tidy rows of wood, metal or brick beds with ample vegetable growth in each section. However, as with any type of gardening there are benefits and there are drawbacks. Let’s look at some of them. We’ll also go into the key components to consider when planning your own raised beds.
Pros of raised beds
Soil management
If you have poor soil or soil you don’t trust due to contamination issues you can bring in and improve soil in a raised bed far more easily than in-ground.
Soil warming
Raised beds tend to warm more rapidly than in-ground beds which is beneficial for longer seasons. Plus, the delineated size and shape make for easier season extension by using row cover or creating low tunnels (see supports for covers in the image).
Accessibility
Raised beds make a distinct area for garden space and pathway space which can help those with mobility issues get into the garden more easily. Beds can be raised as high as needed (although the bigger they get the more fill soil you may need!)
Higher yields with block-style planting
When planting in a block style you can get a higher and earlier harvest when combined with the warmer soils.
Less area to weed due to high plant density
Block style planting reduces the amount of bare soil in a garden space reducing your need to weed. Plus, if you manage your soil well you may not have a lot of weed seeds in your garden soil!
Reduced soil compaction
Because the space is delineated as garden bed vs. walking bed you won’t be tempted to walk over it or step on the beds as frequently meaning that you will have less compaction to manage over time which leads to better water management and root development in your plants!
Architectural interest
Finally, raised beds can look very nice especially when paired with an aesthetic mulch in the pathways and good care over time.
Cons of raised beds
You have to build them!
Potentially expensive
Fill soil, bed material can both add up in cost rather quickly. Many gardeners may start with ambitions to build 10-20 raised beds but finances hit, and they end up with fewer, or build them gradually over time. Realistically a 4’ x 8’ garden bed that is 12” above ground level may cost between $50 and $500 to build depending on the materials you select. Fill material as well may not be inexpensive. If you can pick up topsoil yourself you can save a lot, but many landscape supply companies charge several hundred dollars to deliver material.
May not last a long time
This is also dependent on the materials you select, but if you’re working with wood you may need to re-do your beds every 5-15 years. Even solid materials like concrete or brick may settle or shift over time requiring re-building.
Increased water needs
As the soils in a raised bed tend to warm more rapidly they often also drain and/or evaporate more quickly so may require additional water when compared to in-ground beds.
Need to monitor nutrients
When watering more you may be flushing nutrients down below the rooting area of your plants so you may need to consider fertilizing more lightly and more frequently. Obviously regular soil tests from a soil testing lab will give you the most specific information on nutrient needs of your soil.
Soil may cool faster
While soil in raised beds warms faster in the spring, the reverse will also be true, and the beds will likely cool more rapidly in the fall as temperatures drop.
Limits bed size
While theoretically raised beds can be any size, like most gardeners, you may have budgetary or logistical limitations which may mean that you cannot have as much garden space in raised beds as you could support with in-ground gardens. By using planting styles such as block-style planting, and practicing succession planting, you can increase yield in smaller spaces.
What to know when planning and building
So, you’ve looked at the lists above and decided that raised beds are for you. What do you need to consider?
Size
Raised beds can be made in a variety of sizes, some are easier to manage than others. In general, it’s good to limit size to some capacity. Beds that are no wider than 3-4’ wide are ideal for gardening because most people can reach across them (if you’re a lazy gardener like me, having to get up and walk around a bed to pull a weed on the other side is just TOO much!). Having a raised bed more than 12’ long may be challenging depending on the material you use to build it, but theoretically there is no reason to limit bed length. Typically, beds are between 6-12’ long. Depth can be dependent on your needs. You can get some of the benefits of raised beds with as little as a 6” height, but it’s possible to make beds 24” tall or higher if you want access from a seat or wheelchair. If your beds are large, it may be worthwhile to install support in the middle in a few places to reduce bowing that can happen over time, especially with materials like wood that can flex and warp.
Materials
Many durable materials can be great choices for raised beds including wood (hardwood will last longer than softwood), pressure treated wood, metal, concrete, bricks/blocks, stone or more. Even piling soil up into a raised area can give some of the benefits without building a frame. If using pressure treated wood, it is safe – provided you use new pressure treated lumber which is treated with copper rather than Chromated Copper Arsenate that was used before 2004. If you’re in doubt about your lumber use it for another project and purchase new pressure treated lumber for your garden beds.
Fill
Native soil or quality topsoil from your local landscape supply company are great options. If you aren’t raising your bed dramatically you may be able to shift soil within your own yard. Filling can be an expensive part of the process but it’s important to get good, well-draining, mineral-based soil (typically this is called topsoil). Many websites promote the use of logs/ leaves/branches or other organic waste at the bottom of the beds to fill more of the bed; this is often called hügelkultur. In some areas this could be OK, but over time the organic material will decompose, and you’ll need to top up the garden bed anyway. Putting a lot of stable high carbon organic material in the soil can offset the Carbon: Nitrogen ratio which can lead to nutrient issues in your vegetable garden, so it is best avoided. Additionally, it’s not ideal to use a large proportion of compost as fill in a garden bed because it may be dense and it likely will be too high in nutrients for good plant growth. A little (1/2” to 1”) compost in the bed can be a good idea if your organic matter is below 3-5% but avoid filling it all with compost.
Combine native soil with topsoil by double digging whenever possible. Double digging is when you dig the top 8-12” of soil and move it to the side and then dig/loosen the next 8-12” of soil underneath. Thankfully this task need only be performed once, and is best done by younger backs if you have a teenager who owes you favors. Unless you are raising your beds to avoid burrowing pests such as voles or cannot plant in your native soil due to toxicity concerns, allowing movement between your top fill and the native soil will lead to better root development over time. There is no need to place a layer of plastic, landscape fabric, or cardboard at the bottom of your new raised bed. See the image for an example of a common practice – by placing the landscape fabric under the bed you are creating a large container with a very shallow rooting area which will lead to struggling plants. Better to eliminate the landscape fabric completely and let fill soil and native soil mix when possible.
While this went into a lot of detail there are still always additional things you can learn – if you have more questions, you can reach out to your local Extension office for specifics and assistance.
Ready to Plant? Check out our additional resources:
Eight easy plants to grow for donation
Top 5 vegetables requested by hunger relief organizations
🌱 Find all of Fresh Food Connect's Resources for Gardeners here
🥕 Gardening in Colorado? Check out CSU Extension's Grow & Give program for more information on growing to share for hunger relief in Colorado.
Your garden can make a difference!
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