Water is the most critical element for plant growth. Without it crops cannot grow. It can also be the most limited and precious resource, especially with expected higher temperatures and irregular rainfall patterns made worse by global climate change.
Globally, rain-fed agriculture uses only 35–45% of the rain that falls; in some areas of sub-Saharan Africa, this amount drops to 15–20%. The question is not how to access more water, but rather how to improve water use efficiency, especially in areas where the amount of land available for planting crops is limited.
Even in dry locations, a lot of rain can fall on a small piece of land: 1 mm of rainfall converts to 1 L of water per m2. This means that in a region that receives only 150 mm of rainfall each year, there are 150 L of water that fall per m2. In other words, assuming a typical rainy season, 2,400 L of water fall directly on a 4 m by 6 m garden, which is more than enough to grow a wide variety of crops. And this does not include all the rainfall on the rest of the land upslope from the garden, which can be directed into the garden to increase moisture availability.
Effective water management also decreases soil erosion. Unmanaged rainfall hits the land and flows over and out of the garden, taking the soil with it. Over time, a lot of nutrients and soil are lost due to rain. By effectively managing rainfall, the impacts of erosion are minimized and the nutrients and organic matter built up in the soil can remain in the garden.
The level of soil erosion caused by water is represented on the soil erosion triangle. A farmer can reduce the amount of soil erosion by slowing the water’s speed, by reducing the volume of water moving across the land, or by reducing the depth of water moving across the land. A garden design that manages the rainfall will not only capture the rain for the garden, but will also prevent the top soil – and its nutrients – from flowing off the site.
The permagarden design allows for the efficient capture and retention of even the most minimal rainfall through micro-catchments (small methods to capture water). At the same time, it allows for the safe and easy removal of excess water to minimize erosion or flooding. The design is also based on the efficient reuse of household wastewater and other practices that conserve water in the garden. The key is for a gardener to make the most out of the available water, which involves minimizing water runoff, evaporation, and waste, and allowing it to enter the soil. Water can be captured from several sources, including:
Household spare water management.
Rainwater harvesting is the capturing of rain that falls on the land. It requires the gardener to design the land and implement a planting approach to prevent rainwater from leaving the garden site through a collection of practices, including swales, berms, half-moons and catchment holes. In dryland areas, the gardener’s aim is to retain all the rainwater that falls or flows on his or her land.
The first step to effective rainwater harvesting in a permagarden is to understand the three key ‘S’ principles of water management: Slow, Spread, and Sink.
Once these principles are understood, a gardener can identify his or her main sources of water and then implement the best range of practices to utilize those resources.
Slow, spread, sink
Effective water management in the garden begins with the three ‘S’ principles: Slow, Spread, Sink.
Slow the water down so it can infiltrate into the soil. Once the water falls on the land, the gardener needs to slow the movement of the water. Slower-moving water has a much better chance of providing crops the moisture that they need than water that flows over the surface of a garden and runs off. Mulch, swales, rainwater catchment holes, and half-moons are all practices to help slow the water.
Spread the water across and through the soil so all plants can use it. Water that infiltrates slowly is able to spread throughout the soil profile, providing more plants and roots with access to moisture and nutrients required for optimal production.
Sink the water deep into the soil. By implementing water-holding practices throughout the garden (swales, berms, holes, and other micro-catchments), captured rainwater is encouraged to sink and infiltrate deep into the soil. The deep soil quality in permagardens also enables water to sink far deeper into the soil than in conventional approaches. In effect, double digging stores water in the soil and helps roots grow deep to access it, especially in drier conditions when normal gardens may have already dried out.
Adding straw reduces water loss through evaporation and water runoff (above).
Understanding the contour of the land
A key idea behind designing and building a permagarden is to understand how water will enter and flow through the land. By understanding the flow of water, the gardener will be able to more effectively slow, spread, and sink the water, leading to increased water capture and less soil erosion. One good way to do this is to find the contour across the slope and build micro-catchment structures to both control and capture the rainwater. A contour line is defined as a line
whose every point shares the same elevation, such that water flows perpendicular to the contour down the slope. Even land that looks flat likely has some slope, and a gardener should always find the contour when designing and building a permagarden. To begin measuring contour lines for a permagarden, a gardener should start at the top of his or her garden and work down the slope. Starting at the top ensures that there is less volume of water and that the water is moving as slowly as possible before it is brought into the garden.
Building and using A-frames
An A-frame is a low-cost, yet valuable tool that gardeners can use to determine the contour of the land to effectively design a permagarden.
How to build an A-frame
- Gather three sticks (two at least 2 m long and one 1 m long), a few nails, twine, and a small rock. The sticks can be bamboo, cut boards, or taken directly from a tree. They should be thick enough to not break when nails are put into them or bend when used in the field.
- Nail/tie the two longer sticks together at one end with the opposite ends approximately 1.5 m apart. In place of nails, thin strips of bicycle inner tube work well to lash the sticks together.
- Nail/tie the 1 m stick halfway down each of the two longer sticks,
connecting the two longer sticks together. This should create a capital ‘A’ with the sticks.
- Nail one end of the twine at the top of the ‘A’ with the string flowing down the middle of the A-frame, approximately 30–50 cm past the middle stick.
- Tie a rock at the end of the twine. The rock should be sitting 10-20 cm below the bottom of the middle stick.
- It is now time to calibrate the A-frame.
- First, put one leg of the A-frame on a flat, elevated place approximately 10–15 cm above the ground, while the other leg is on the ground. The elevated leg can be put on a rock, stick, or just an elevated piece of land. Make sure the A-frame is stable. Mark a light line where the string crosses the middle stick.
- Next, put the other leg at the exact same elevated spot and put the second leg on the ground at the same spot where you put the first leg. Mark a second light line where the string crosses the middle stick.
- Finally, put a line halfway between the two light lines on the middle stick. Make this mark bold so it stands out. This will be the center of the A-frame.
The gardener can now use the A-frame to determine the contour of the land:
- Start at the highest point in the garden site, at one corner of the garden. Place one leg of the A-frame on the ground and put a stake, small stick, or rock at that point. Digging a mark with a hoe can work in the absence of other items.
- While keeping the first leg at the starting point, move the second leg until the twine is exactly on the center line on the middle stick. Put another stake in the ground at that point. These first two stakes share the same elevation across the slope and are the beginning of the first contour line.
- Keep the second leg at the last marked point on the ground and rotate the A-frame, moving only the first leg, until the next point in the garden that centers the twine in the A-frame is found. Mark the third point with another stake. At all times, at least one leg should be at a marked point on the contour line.
- Continue this process until the other side has been reached, resulting in a contour line across the length of the garden site.
Determining contours of the land using an A-frame.
Photograph: Thomas Cole
The line that connects all of the stakes in the ground is the contour line and is continually at the same elevation. This process can be repeated as many times as desired to find contour lines throughout the land. Once a contour line is
Digging a swale.
Photograph: Thomas Cole
known, then water micro-catchment structures such as swales and berms can be constructed to slow, spread, and sink the water.
Rainwater harvesting practices
Swales, berms, half-moons, basins, and holes are agriculture practices that can be integrated into the design of a permagarden and work to slow down the water, which allows it to spread and sink slowly through the soil profile. It is then readily absorbed within the amended soil of the permagarden bed. In extremely arid areas, rainwater harvesting practices (swales, half-moons, basins, or holes) can be used as planting areas to accumulate enough water to grow a crop (see page 35).
Swales are an important rainwater harvesting tool, especially in dryland regions where the goal is to store 100% of the rain on the land. Contour swales are shallow trenches dug along the contour to capture rainwater as it flows down the slope. Drainage swales are also shallow trenches, but are measured and dug with a slight slope to the swale (i.e., not perpendicular to the slope). Drainage swales help divert water away from a problem area or toward a larger water catchment basin. Drainage swales are useful in areas of heavy rainfall, where problems with flooding exist around the permagarden or the homestead. The water-holding capacity of a swale is greatly increased by building earthen berms on the downslope edge of the swale (see page 13). Swales are a good strategy in resource-poor environments due to their minimal cost to construct and maintain, and their overall effectiveness in capturing and directing water. When digging swales, it is important to remember to design and build an overflow route.
In times of heavy rains, planned overflow routes enable water to safely move down slope.
Swales and berms may not be straight.
Photograph: Eric Carlberg
The number, design, and size of the swales are up to the farmer, and depend on the maximum amount of water that may need to be captured. There is not an exact order or way to design swales. Design and construction of a permagarden’s swales was already discussed (see page 13).
A berm is a raised earthen structure, often placed downhill or beside a swale. The primary functions of the berm are to help protect a garden from runoff water and to store more water in a given area. It is effective in a permagarden, as well as in the larger landscape around the homestead or in the main farm field. It is constructed by mounding soil in a line along the contour, or in small half circles called half-moons. Using the soil dug out from a swale, a berm can greatly increase the capacity of the micro-catchment system to catch water. Berms also play another key function in the permagarden. By amending the soil within the
berm, much in the same way as for the garden beds, they become a vital space to plant medicinal, nutritious, or culturally important perennial plants and crops. In areas of heavier rainfall, berms can act as a raised path to walk.
How to amend and plant a berm
- Standing over the beginning of the smoothed berm, loosen the soil down to the compacted subsoil.
- Remove a 50 cm wide portion of this topsoil and place it on a grain sack or in buckets for later use.
- Stand to the side, facing the exposed subsoil, and loosen this subsoil as deep as possible (a further 30 cm is sufficient).
- Amend the subsoil with several handfuls charcoal, manure, and wood ash. Mix well.
- Again standing to the side of the berm, remove the next 50 cm of loosened berm topsoil to expose the next section of subsoil.
- Amend the subsoil and then pull the topsoil down the entire length of the berm.
- Return the initially removed topsoil to cover the final section of amended subsoil.
- Rake the entire surface smooth and flat.
- Amend each meter length of the berm with half a bucket manure,
a quarter of a bucket of charcoal, and several handfuls of wood ash. Mix all amendments into the top 20 cm of the berm.
- Water the berm with one 20 L watering can or bucket.
- The berm is now ready to plant with useful perennials and annuals.
Boomerang berm Mazvihwa Zimbabwe.
Photograph: Brad Lancaster
Half-moons and basins
Half-moons and basins are other micro-catchment strategies to harvest and retain rainwater, particularly in dryland regions. (In some areas, half-moons are referred to as boomerang or even ‘smile’ beds because of their shape, while in the Francophone area of the Sahel, where they are found in widespread use, they are known as demi-lunes.) Half-moons are small, generally 2–3 m, curved berms or ridges in the shape of a semi-circle. The end tips of the half-moon are located along the contour of the slope, pointing uphill. Multiple half-moons can be placed in a row across a field or at the top a garden to trap the flow of rainwater. A second row is then placed below, though staggered to catch any overflow that continues down the slope. The area within the half-moon, and even the berm itself, is often amended with compost, manure, or other amendment, and planted with annual or perennial crops. Half-moons are important structures around the homestead and permagarden as they create viable planting areas for fruit or medicinal trees. Basins are similar in concept and practice, though the berm, or ridge, of the basin itself is closed in a circular shape to form a basin.
Rainwater catchment holes
Catchment holes are a critical part of a permagarden, both to harvest and store rainwater and to catch any overflow from the swales. They are usually placed at the ends of the berms and swales and help form part of the protective barrier for the permagarden beds at the center of the garden. The catchment holes should be dug at least 50 cm deep (deeper for areas with greater rainfall) and 50-100 cm wide. As with a berm, the downhill edges of the catchment hole can be amended and planted, increasing the hole’s functionality and use to the gardener. In dryland climates, more shallow and narrow catchment holes are often dug across an entire field, amended with compost or manure and planted with sorghum or maize. Different than a hole whose primary purpose is to store water, these planting holes are the primary crop-growing area for many farmers in dryland environments, especially in West Africa. In this region they are called zai or tassa.
After the gardener designs the land and integrates rainwater harvesting practices to capture the rain, additional practices should be added to retain the water.
Especially in hot climates, a lot of water can be lost due to evaporation.
A gardener should not burn crop residues, grasses, and weeds in a permagarden, or even in their main cropped fields, because it causes the garden to lose a lot of moisture to evaporation and runoff. An important way to maximize water capture
Organic mulch keeps the soil cool and moist, compared to uncovered ground.
Photograph: Thomas Cole
and retention is to keep some form of cover on the field at all times, such as mulch or crop residue. This is critical in both the rainy and the dry seasons. Once water enters the field, the goal should be to preserve as much of that moisture for as long a period as possible, helping keep the temperature of the soil low, even during hot, dry weather, thereby slowing evaporation rates. This moisture retention is often enough to get crops through extended dry spells in the rainy season. Additionally, soils protected in such a manner can conserve remarkable amounts of water for the following crop.
Mulch is a covering for the soil that helps conserve moisture, lessen weeds, prevent erosion, and improve soil structure. Good organic mulch consists of leaves, grass, straw, compost, banana leaves, maize or sorghum stover, bean stalks, and/or other reusable materials found close to home. A 3–5 cm layer of mulch added to the surface of a permagarden’s beds can help in important physical, biological, and chemical ways, as described below.12
Helps regulate the temperature by keeping the soil cool and moist. Prevents weeds from growing easily, leaving more water and space for growing crops.
Stops the force of raindrops, preventing erosion and allowing rainwater to sink deeply into the soil.
Serves as food for good microbes, which provide many values to the soil, as well as important ‘housing’ for beneficial insects and earthworms.
Regulates soil pH.
Releases nutrients into the soil.
How to apply mulch
- Gather leaves, crop residue, and/or dry grasses.
- Keep them in or near the garden.
- Place a 3–5 cm layer of dry material around the base of plants, including trees. Make sure to keep the material a little distance from the stem or trunk itself (about 5–10 cm), as placing mulch too close to the stem or trunk can lead to fungal problems.
12 In addition, a gardener could grow living mulch, which would act as a cover crop and help retain water in the garden.
Contour berm and contour plantings, Mazvihwa Zimbabwe (right).
Photograph: Brad Lancaster
- Any material not placed around the plants can be left on the soil surface to keep the sun off the soil and to prevent erosion from rainfall impact.
Many things can be used as mulch, but it is important that the materials be dry. Wet, green plant material can be used, but if it is placed too close to stems or leaves of growing plants, it can cause them to rot. Therefore, if using green materials as mulch, make sure they are placed away from tender stems and leaves.
- All bare ground, including pathways and the main garden fields, should receive some form of mulch. Whenever possible, mulch in these areas can be thicker (5–10 cm) to help weed suppression and moisture retention.
Land preparation and planting
How a gardener prepares the garden beds and plants will affect the amount of water retained in the garden. A few practices leading to increased water retention include:
Preparing the soil deeply (double digging). Adding compost to the garden beds.
Planting and managing trees around the garden.
Practicing close plant spacing, which provides more foliage coverage in the garden beds, leading to less evaporation (more on page 41).
Preventing and removing weeds in the garden.
Household spare-water management
Gardeners are sometimes able to gather water from other sources around the household, such as from a borehole, stream, or waste water. There are several practices gardeners can do to maximize the effectiveness of this water in the garden while using minimal resources.
Plastic water bottles allow water to slowly seep into the root of plants.
Photograph: Peter Jensen
Household spare-water-management practices
Plastic water bottle
Besides irrigating by watering can or other container in the garden, a plastic water bottle can be used to slowly add water directly onto the roots of a plant. This is a simple, localized form of drip irrigation for a single plant or a group of closely sown plants. A small hole or a group of small holes in the bottom of the bottle allows water to slowly drip or seep into the root zone of the targeted plant or plants. This method is very effective when water is in short supply and needs to be rationed in the garden. It also works well to help irrigate newly planted trees.
How to use the plastic water bottle
- Find an empty 500 ml or 1 L plastic water bottle with a good cap.
- Using a sharp knife or a thin nail, make a few small holes on the side of the bottle, 1 cm from the bottom.
- Fill with water and replace the cap. Notice that the water does not come out if the cap is on tight.
- Twist open the cap slowly until water comes out.
- Bury the bottle 10 cm deep—into the root zone—near a vegetable seedling. A 1 L bottle is enough for three plants (tomato, pepper, eggplant, cabbage, and kale, for example) if triangular spacing is used (see page 41).
- Open the cap a little more until bubbles can be seen coming up inside the bottle. This means that water is now slowly coming out through the holes in the bottle.
- Cover the entire area with water-conserving mulch.
- Add water to the bottle every 2–3 days, depending on moisture levels in the soil, making sure to leave the bottle in place. As the moisture level increases in the soil, the water will come out of the bottle more slowly. The rate that the water will come out of the bottle will increase only as the soil becomes dry, as the plants take in more water through their roots.
- The bottle can also be hung in the air tied to a stick about 15 cm above a plant.
Another good practice for irrigating permagarden beds is to use clay pots buried in the soil. This technique works best in the dry season as a way to conserve and use less water while still being able to grow vegetables. In dryland environments, this approach can prove very useful, as the pots need to be filled with water only about twice each week.
How to use the clay pot method
- Before planting, dig unglazed clay pots (20–30 cm in diameter) into the bed, spaced anywhere from 50 to 100 cm apart. Bury the pots so that the soil line is level with the top of the pot.
- Sow seeds or transplant seedlings at the proper interplant spacing for the given crop. Place seeds 10 cm from the edge of the pot and all around it. There should be four plants around each pot.
- Fill the pot with water. Cover it (with a banana leaf or dry grass, for example) to prevent evaporation. Household wastewater works well here, as the clay pots help filter the water before it reaches the plant roots.
- Make sure to water seedlings when they are first planted. Water in the clay pots will then seep through the pots to the soil and reach the seedlings’ roots.
- Refill the pots with water as needed (usually around twice a week).
Household waste water
In many areas, it can prove difficult to provide enough water to a permagarden on a sustained and regular basis, particularly during dry seasons. With care, wastewater can be reused to help irrigate parts of the garden and can be an important additional water source for moisture for crops’ roots. Wastewater should be poured onto the soil around plants; do not throw it on or over the garden. It is especially important to keep the water off plants’ leaves as much as possible; many plant diseases need moisture to thrive. It is best to put the
wastewater on a mulched garden bed, because the mulch helps filter any soap or impurities in the wastewater.
Possible sources of wastewater:
Dishwater from cleaning dishes. Bathing water.
Water from washing and rinsing clothes.
Using wastewater can be a practice that is sometimes difficult for a farmer to adopt due to cultural norms or habits. If the gardener is not comfortable putting the waste water directly on the garden bed then they can put it in the swale or a basin with a tree planted.