Becky Weeks - Jan 29, 2021
8 Advantages of Raised Bed Gardening
My first introduction to raised bed gardening was through reading gardening magazines that featured beautiful, glossy photos of cedar-framed beds just overflowing with flowers and healthy vegetables. “Those are lovely”, I thought to myself “but I have far too much garden for something like that.” Some years later, I was again introduced to the raised bed gardening concept, this time by my favorite gardening author, Steve Solomon. As it turns out, I had been mistaken. Raised beds were not just a beautiful feature for urban landscapes (and magazines), but a useful technique for growing nutrient-dense food with less effort. For the last decade, I have been using raised beds in my own gardens and I believe it has been the key my success in raising large, productive gardens without so much stress. In this article, I’ll discuss some of the benefits that raised beds offer and why you should consider giving it a try.
What is a raised bed?
A raised bed is simply a bed where the level of the soil has been elevated. It could be framed out in wood, composite, metal, or not at all. Usually, it is at least a few feet wide and the length can be whatever you need it to be, or whatever your space can accommodate. The soil surface can be raised by several inches, or barely at all. However, raised beds have one common feature…you never, ever walk in them.
Benefits of raised beds
There are a number of benefits to using raised beds. The one most people think of is not having to bend over as much. But, as we will detail in this section, the raised bed offers many benefits to both the gardener and the garden.
Less soil compaction
As I previously mentioned, the one rule of raised bed gardening is to “Stay out of the bed!” I say this with added emphasis because those words are probably still echoing throughout the valley from my repeated warnings to our 2-year-old last summer. You should have seen her defiantly skipping down the middle of the bed as she looked straight at me, smiling. Anyway, the raised bed is a no-go-zone for human feet, and paws, for that matter. Treading on the soil causes soil compaction, pressing the soil particles together and leaving less space for water and air. By walking only in the pathways, you ensure that the soil in the bed stays fluffy and aerated, giving your plants’ roots access to plenty of air and water.
The Secret Lives of Plants
We all were taught that plants take in water and carbon dioxide and then convert them into sugar and oxygen using a process called photosynthesis. But the lesser-known fact is that plants need oxygen too. Without it, they can’t convert those sugars into energy. So how do roots get oxygen without photosynthesis? They take it in through small pockets of air in the soil. This is the reason why plants cannot survive having their roots submerged in water without some sort of biological adaptation (or artificial adaptation in the case of hydroponics.) Soil compaction is harmful because it reduces the size and number of air pockets available to the plant’s roots.
Increased water efficiency
Imagine you are on a construction site one sunny morning. You look down and there is a big, wet footprint in the soil. You think to yourself, “Why is this footprint still wet, while the soil around it is dry?” Well, the answer is capillary flow. Capillary flow or capillary rise occurs when soil particles are pressed together creating a path for water to move up through the soil. As the sun warms the surface of the soil, water evaporates from it, and capillary forces pull additional moisture up through the soil. This is bad if you are trying to keep the moisture in the soil, however as I will discuss in a future post, you can sometimes use capillary flow to your advantage.
One major benefit of raised beds is that they improve drainage. If you live in an area with clay soil, raised beds are perhaps the best option for improving drainage. Raising the level of the bed, by adding organic matter and aerating, lifts some of the plants’ roots out of the damp, dense subsoil and gives them access to much-needed oxygen.
Getting fertility where it's needed
The raised garden bed has one major benefit when it comes to improving soil fertility—you only put soil amendments where they are needed. Manure, compost, and other amendments can be expensive. Even if you produce your own compost, you don’t want to waste it on walkways. Additionally, many nutrients are immobile in soil. For your plants to take advantage of these nutrients, you need to put them where they are needed. By using raised beds, you can increase the depth through which your soil amendments are incorporated, making immobile nutrients accessible to a greater proportion of the plant’s roots.
A. Comparison of beds at planting Light brown areas are walkways. Square = 1sf
B. Same beds a few weeks later. The raised bed holds 275 beet plants while the conventional bed holds just 225.
C. At maturity, the canopy completely covers the raised bed, so weeding is seldom needed.
When you use raised beds, you can grow more plants in less space. The figure above shows two similarly sized beds of beets, both around 100 square feet. The raised bed holds more plants (275) compared to the conventional bed (225). This is because conventional beds require you to allow more space between rows to accommodate the gardener. In this conventional bed, for example, the row spacing is a narrow 18 inches, which would still be a bit difficult to weed once the plants are a bit taller. Row spacing within a raised bed, on the other hand, can be as narrow as you want (although ideally, no narrower than your hoe) because you don’t need to walk between the rows.
Easier work and less of it
Speaking of weeding, did you notice the other benefit of the raised bed? The gardener can stand sideways with their feet comfortably spread and pull the hoe straight towards them. Oftentimes with narrow conventional rows (especially when the plants are bigger) you find yourself trying to reach over a row, pulling the hoe along beside your body. It’s very uncomfortable and not very precise. Working with a short, perpendicular row is also easier when planting. No need to drag out a sting-- just press your hoe into the bed to make a nice channel for the seeds to sit in.
Also take note of the dark soil in the raised bed. This is the soil that has not been walked on. It is light and fluffy so the hoe glides through it with ease. Weeding in compacted soil, on the other hand, is hard work. Sometimes you feel as though you’re trying to bludgeon the weeds to death rather than uprooting them. I’ve done it both ways and I much prefer weeding a raised bed.
Finally, at maturity the raised bed is fully covered by the plant canopy. By late spring, there will be little work to do besides harvesting what you’ve grown. Conventional rows will still have exposed soil that needs to be cultivated and since it has been walked on, it will take some work.
Making a seed furrow in a reworked bed
The beds can be reworked in minutes
I still remember harvesting a bed of onions that first year I started using raised beds. I pulled the onions, cleared away the remaining debris with a wire rake, and smoothed the surface with the flat side of a stiff rake. With that, I was ready to sow fall greens. It was wonderful! Whereas in the past, I had to drag out the tiller to re-work beds, my raised beds were ready to replant within minutes of being harvested. This convenience may be hard to appreciate now, but keep in mind that some of the gardening excitement will have worn off by the time you harvest your mid-season veggies, and the added effort of re-tilling just might be enough to prevent you from planting that fall garden you’ve been wanting.
Planning your raised bed garden
Have I sold you yet? If you are planning on giving raised bed gardening a try, here are a few things to consider before getting started.
How big should my raised beds be?
The most common width for a raised bed is 3 to 4 feet. You want the bed to be narrow enough that you can comfortably reach the middle from either side. I have used both 3’ and 4’ beds. I felt that the 4’ beds were more efficient, but I prefer the 3’ bed because I can access it easier. Sometimes, I find myself straddling my garden beds, particularly when I’m doing delicate weeding or planting onions, and while I could probably do this with a 4’ bed, getting myself out of that position would require some assistance. By the way, there is no rule that says your beds must all be the same width. It may be best, for example, to plant cabbages and Brussels sprouts in 2’ beds and greens in 4’ beds. You can do it however you’d like.
The length of the bed doesn’t really matter. I like to target the total bed size for 100sf so I can easily calculate amendments and I don’t like my beds so long that walking around them is akin to running a marathon, but otherwise, I don’t think the length matters much.
The depth is also variable. Up to a certain point, deeper is better. You don’t want the soil washing down into the walkways, but you also want the bed to be tall enough that you can easily see where the walkways are. As I will discuss in the following section, it is possible to have a raised bed without actually raising the level of the soil. If you have a very large garden or are physically restricted in some way, this may be the best option for you.
How to make a raised bed
There are four common methods for making a raised bed:
1. Raising the surface by bringing in soil, manure, or compost
2. Lifting and aerating the existing soil using a broadfork or garden fork
3. Excavating the walkways and tossing the soil into the beds
4. Double digging the beds
Making raised beds does require some physical labor. When I did it manually using the third method, it would take me an afternoon to excavate and hill up 1000sf of beds. However, once the bed is made, you don’t have to remake it every year. You can just rework the area within the bed using a small tiller, garden fork, or broad fork.
As previously mentioned, if you are not physically able to shovel or use a garden fork, you can still benefit from raised beds. Just mark out your beds using twine, a line of sand, or chalk dust and stay within the walkways for the first couple weeks of gardening. Eventually, the footpaths will become clear and you will no longer need the marker.
Maintaining the walkways
There are some options when it comes to maintaining walkways. They can be mulched with grass, straw, or newspaper or they can be left bare. The soil in this space will eventually become compacted and will be more difficult to weed than the rest of the garden. If you can afford one, a mantis tiller, or something similar, makes quick and easy work of weeding walkways. Otherwise, a sharp hoe will do the trick.
Planting your raised beds
Raised beds offer a lot more options when it comes to planting. You can plant perpendicular to the bed or in parallel. Your parallel rows can be singular or paired, with plants staggered or straight-on. You could even broadcast seed into a bed if you wanted. I have heard of people doing this successfully with lettuce and other greens. The point is this: the options are endless. Here are some of the configurations that we commonly use with our 3-foot raised beds.
|Vegetable||Row Orientation and Details|
|Beans (Bush)||Parallel with two rows per bed spaced 18" apart|
|Beans (Pole)||On a cattle panel that spans two beds such that the gardener can stand in the walkway beneath the panel.|
|Beets||Perpendicular with rows spaced 12" apart|
|Broccoli & Cauliflower||Parallel with two staggered rows per bed, spaced 18" apart|
|Cabbage||Parallel with two staggered rows per bed, spaced 18" apart|
|Carrots||Perpendicular in rows spaced 12" apart|
|Cowpeas||Parallel with two rows per bed spaced 18" apart|
|Cucumbers||Parallel with a single row running down the middle of the bed. Cattle panel may be staked lengthwise down the bed for support|
|Herbs||Perpendicular in rows 12-18" apart, depending on the herb|
|Kale & Sprouts||Parallel with two staggered rows per bed, spaced 18" apart|
|Kohlrabi||Perpendicular with rows spaced 18" apart|
|Lettuce & Greens||Perpendicular with rows spaced 12" apart, 18" for heading lettuce or chard|
|Onions||Perpendicular with 12" between rows|
|Peas||Perpendicular in paired-rows grown on a short trellis. 6" between pairs and 24" between trellises.|
|Peppers & Eggplant||Parallel with two staggered rows per bed spaced 18" apart|
|Radishes||Perpendicular with rows spaced 12" apart|
|Summer Squash||Parallel in a single "row" with a cluster of seeds (or hill) every 4-feet|
|Tomatoes & Tomatillos||Parallel with one row per bed and a mulched, fallow bed between rows.|
|Turnips & Rutabaga||Perpendicular with 24" between rows|
Plants that don't do well in raised beds
While pretty much any plant can benefit from having loose, deep soil, some plants are not suited for growing in raised beds. Winter squash and melons for example, can produce vines that spread across multiple beds. They are best planted in their own area where they have space to run. Corn can be planted in a raised bed, but doing so is somewhat impractical. Corn also anchors itself with brace roots and having firm soil for them to latch onto seems to help with lodging.
In summary: Why use raised beds
Growing a garden in raised beds offers many benefits for both gardeners and their plants. Raised beds reduce compaction, improve water efficiency and drainage, make more efficient use of soil amendments, and they accommodate more plants than conventional rows, all while requiring less work. Should you decide to put in a little extra effort creating raised beds for your garden, you may find even more benefits for your garden.
Becky Weeks, Ph.D.
Geneticist, Gardener, Founder of Thresh Seed Co.
Becky is a geneticist with a passion for gardening. Prior to starting Thresh Seed Co., she spent fifteen years researching plant genetics and development, later applying those principles to aid in the breeding of commercial corn and soybean varieties. She lives on a farm in Iowa with her husband and two children, where she enjoys growing just about anything and experimenting with the breeding of new vegetable varieties.