Written by Doug Crouch
To extrude upward the earth for creating favorable growing conditions is the action and intent behind creating a raised bed. While a very common feature in a permaculture landscape, we must check, as always, that they are climate and context appropriate. If so, this common gardening earthwork comes in many forms and fashions from a few square meters to kilometer long lines for tree crops. They are easy to build and with a few tips, relatively easy to maintain. Their advantages of improving drainage and warming soil temperatures earleir in the season make them a great season extender and general earthwork. This is especially true in more humid climates, poor draining soils, or at specific times of the year in other climates where humidity is seasonal (i.e. Mediterranean). Their fertility can be maintained in numerous ways including chicken tractors, their construction can be with or without boards or logs along the side, and they can be straight line beds in zone 3 or curvy waves of a mandala garden in Zone 2. They can also be dramatically raised in boxes so the needs of the elderly and handicapped are met thus meeting the important function of social inclusion. With raised beds exposed edge, again, they do dry out and warm up quicker, which is a plus in some climates, but in others it creates a painful watering habitat. So be sure this is the right earthwork for your soil type, for the right time of the year, and for the climate.
Why Raised Beds?
Building raised beds is a northern European technique, in general, where humidity persists throughout the year. They have short growing seasons, especially for summer crops like Tomatoes or Peppers whose origins are in Central America. The water table is often quite high and soils can be heavy and quite poor draining. So as you can see the obvious response is to elevate the growing space to deal with such factors. Imagine climates and contexts like England, Holland, and Belgium and from there the tendency to make raised beds makes sense.
Moreover, spring rains are a blessing for our cool season crops as they can deal with the temperature fluctuation of spring and thrive in this cooler and wetter environment. As the days get longer, especially around the time of the spring equinox, the daylight hours grow rapidly and the plants awaken and take off as well. This daylight lengthening impulse spurs growth but our soil conditions are vital at this time of the year. If the water table is too high, or soils drain too slowly, anaerobic conditions can persist thus causing plant pathogens to build up and cause rot. This can be disastorous for the farmer immediately and for future fertility. The raised bed acts as the mountain in this case as it sheds water while the valleys, or the paths, collect more of the moisture. These spring rains are often accompanied by cold breezes and the rain itself is quite cold. This lowers soil temperatures, which is a huge factor for plant growth at this time of year. As the water drains and the edge is exposed to sunlight the beds can warm up and cool season crops can begin to grow sooner. Also it allows the farmer to put summer crops in earlier, which really need the right soil temperature or they simply stunt from going dormant due to cold soils.
A note on this was working with the campesinos in the Dominican Republic back in 2012-2013. This area broders the subtropics and tropics especially on the north shore where I was farming, teaching, and learning. In the winter months of the Northern Hemisphere, even there amongst papaya and moringa, the landscape experiences a slow down of growth, which I found odd but true. Each day I was encouraged to feel the soil and its true the cooler soils were there in January and early February. However, over time I could feel them warm and you could see the subsequent plant growth as the days got longer and hotter. Furthermore in the Mediterranean climates, where I have farmed in three different continents, I can highly recommend sunken beds especially for summer crops. However raised beds in the winter months will have all of these advantages and allow for year round food production in most regions. This is especially true, again, in areas with heavy clay soils and high water tables. When the rains are waining and its time for warm season crops, switch to sunken beds as to take advantage of the conditions given by that earthwork.
How to Build
While there is tractor implements that build such beds for tree crops and large scale row crop production, I will be referring more to the hand built ones. While I am not opposed to these mechanical implements for initial installment, the process is little more than marking out their initial layout and driving parallel to that. Similarily for the hand-built type, you will also want to do this but you can do it more personal sized. First, most people will orientate the beds east to west to optimize sun exposure. However slope and working with beds on contour may indeed change all of that as each site is unique especially as it pertains to topography, aspect, and access to water. Second, the earthwork itself in terms of dimensions depends a bit on the user. A tall person of over 2 meters may have different sized beds than say the person 1.4 m. Their arm reach is dramatically different. Like any bed, but particularly important in raised beds, stepping on the beds is very counter productive. Thus size the bed appropriately for comfortable arm reach into the bed so you never have to step on it. So take a rope, stick, stone or anything really and put it where you think you would want your pathway. Put your feet behind that and reach comfortably into the area where you will want the raised bed to be. Put a stick there where your hand touches the earth. Remember to only reach comfortability and not everstretch because this is very straining on the body and will eventually cause you to step into the bed. Furthermore, come around to the other side of the bed and stand where you think the next pathway will go. Reach out and if you can comfortably touch the position on the ground where the stick is then place another marker at the front of your foot. Then delineate the lines or shapes of the pathways. If you don’t want straight row beds or have some other context like a perennial crop of Jerusalem Artichokes, you make elect for stepping stones and make the bed bigger. Of course keyholes allow you to increase access in a raised bed system, especially those that are more free form.
From there you simply dig the pathways down and use this displaced earth in the raised bed itself. You may choose to till or disc the whole area first with a tractor making the digging part easier and breaking the earth up. Sometimes this is essential when faced with a large area and a grass and weed infested space. From there, you only need to dig down the pathways about six inches (15 cm) to get an appropriate height for the bed. Going any deeper makes access issues in the future, especially when bringing wheel barrows through. Loosening the earth where the bed will be first is also an option and recommended. The double digging technique that John Jeavons recommends for setting up raised beds is essentially this. From there you will need to do more maintenance to create a permanent feature in the landscape, which is below after several more types of possible implementation variations.
In the implementation, some choose to do a technique known as huggleculture where logs, branches and/ or wood chips are incorporated below the raised bed. This provides a fungal resource and acts as a sponge over time as the woody material breaks down over time. Often the bed becomes quite raised and adequate moisture should be given to the bed in its beginning phases so that the heavy carbon can stay wet so the fungus stays active in breaking it down into a stable carbon compound known as humus.
Raised beds are not only for vegetables, both annual and perennial, but also for tree crops. In some contexts where soils are poor some elect to put trees on raised beds. In humid landscapes this might be in the context of adding swales to the landscape. In drier climates, trees are planted behind the swale but in humid on the swale mound itself. For long rows of trees either mechanical implements or the power of horses or some other draft animal use implements to cast earth upwardly to the downhill side. One can also construct a raised bed solely for an individual tree in a landscape where water tables are dangerously high for some trees.
Also in the design phase you may wish to incorporate swales and raised beds in a combination known as beds on contour. There you use leveling devices to find contour and match the layout of your beds this way. Often this is a more humid landscape technique and on gentle sun facing slopes. The process is the same essentially as straight rows but these take a longer implementation phase with the contour measuring. The pathways become like the depression of the swale and the raised bed is planted accordingly to climate and seasonal variations. More microclimates will be developed as most likely you will have several aspects to the sun. These can be extremely aesthetically pleasing layouts so do consider if possible. They can also help to maintain intensive rains and also as irrigation slumps off the raised bed it is easily cycled into the lower parts of the bed below. If beds are off contour and you notice rainwater and irrigation water flowing down the beds regularly, consider adding or chopping off the end of the bed for a swale like raised mound that is on contour or close to it as to slow the waters descent. Pathways can be quite compacted so do this extra effort to make sure this runoff resource is harvested. In one locale where I have seen this added I augmented the bed in our food forest course to have sub tropical and tropical species as well as biomass crops like comfrey that need this extra water in the mediterranean context.
How to Maintain
Raised beds can be viewed as a semi permanent to permanent feature in the landscape. For most they are permanent features and need to be managed for longevity. This means the soil structure within them needs to be built and fertility maintained and upgraded. Over time both water drainage and capacity to hold water will improve while pest and disease pressure will lessen as the soil food web is diversified and natural capital retained in humus. In the first year this may not be the case as digging raised beds is a disturbance of the soil ecology. Techniques to reestablish that fertility and maintain it could be the following:
- compost tea or extract
- addition of bulk amounts of compost
- cover cropping
- chicken tractoring
- alley cropping with chop and drop to feed beds in relative location (most often tropical)
- mulch, both green and brown
One of the first steps to maintaining a raised bed is to never step on them. That is why building them with realistic dimensions is again very important. Keeping their soil structure in tact also involves lessening and lessening tilling and excessive digging. There are many tools that are alternatives and the one that I use is the broad fork. While maybe not an answer to extensive plots, although labor is labor, this tool will go deep into the soil, about 1 foot (30 cm) or more depending on the design of the tool. It reaches down and aerates the soil without excessive mixing. Over time the process gets easier but dramatically improves growth. It allows for roots to dive deeper and my light mulches at the end of a season sometimes get worked in. This can be done before or after digging the pathways to further prepare for planting in the implementation phase. It is continued as crop turnover takes place.
Another technique I picked up over the years for maintenance of raised beds involves a lessing of the raised effect when the summer heat really comes. Again advantages of raised beds include they warm quicker and have better drainage. However once the summer heat of temperate locations come or the dry season of the mediterranean or tropical places come, the edge of the raised bed can become disadvantagous. Thus mulching intensely the pathways will reduce this edge effect of drying out. So imagine in spring your beds are warmed and planted and the heat is coming on. One can then, as summer approaches, fill the paths with organic matter. In the states at an Urban Agriculture CSA project we used either wood chips or shredded leaves to fill the paths. Both allowed for drainage and were layed so thick that you couldn’t tell the beds were raised any longer. The beds no longer dried out as quick and the paths were sponges of moisture where the worms would migrate when the beds did dry out a bit. These depressions of mulch became like pit gardens almost and the material rapidly broke
down. It was then scooped out in the fall after the fall garden was planted to again bring that edge back into play. The pathways produced compost essentially and the other non broken down material became mulch and would breakdown further in the bed itself. Also by mulching the pathways we would have very little weed pressure along the edges. For market gardeners, this can be a pain so keep this in mind. We also did this in the drylands/ monsoon of Southeast India with Cassava which likes raised beds. The intensely mulched pathways were then sponges of moisture and fertility and were so alive with critters it was a true sight to see after just one week. The cassava needed watered much less and was putting off huge shoots of growth practically immediately. Additionally the mulch on the raised beds no longer slumped off as the pathways were filled. These raised beds were quite small and dramatic so organic matter was always sliding downhill. With the blow downs of “invasive” acacia trees we filled the paths and no longer has this problem.
Also the beds will need mulched to maintain moisture and suppress weeds, which is generally done throughout the year in waves to maintain its effectiveness. This is really important in the fall to seal the winter garden as to prepare for spring. In temperate regions the warming of the soils and spring rains bring intense weed pressure and force soil disturbance through digging or tilling. Thus load the leaves, the cardboard, or wood chips on heavy or the painstaking and backbreaking weeding of spring will indeed be there. Furthermore, if you are growing on a scale where mulching is not feasible grow mulch in place by sowing a cover crop. With a chop and drop of an overwinter overcrop, you can plant summer veggies in a couple weeks later and the site will have been fertilized and mulch created. Mulching keeps moisture in, weeds at bay, and importantly feeds microorganisms. I choose to do both a green and brown mulch to feed both building blocks of the soil food web; the bacteria and fungus. As they breakdown humus is created, fertility boosted, and a reduction of irrigation follows. Lessening our usage of water is a vastly important as we need to keep aquifers full, streams and rivers flowing, and salt buildup lessened. In cold temperate areas one thing I do is in the spring I sometimes remove the mulch for a couple of weeks later in spring to help my beds warm up a bit. This is mainly so I can do direct seeding as to avoid the transplant process. It’s a fine balance so keep up the observation to make sure the uncovering is doing more good than harm.
Overall raised beds are a fantastic choice but again not always contextually appropriate. Remember their seasonal application in some locales and follow the tips presented if possible for implementation and maintenance. Dont get too stuck on the raised bed element as it is just one of many earthworks at our disposal in permaculture design and implementation. The raised bed gives many advantages but work with them when appropriate so they are not burdensome. However they are one of the staple earthworks in a regenerative ecosystem known as a permaculture when contextually appropriate.
Written by Doug Crouch
Header Art Bonita Edwards