Welcome to a new series that will focus on regenerative polycultures for dry and hot climates, which I’ll refer to as Xeric Polyculture. The intention of this series is to provide useful and practical advice for growers in xeric regions of the world and to present a portfolio of plants and polycultures that can be used as broadly as possible within these regions.
We’ll start with an introduction to the xeric regions of the world, looking at the conditions and challenges of growing in these areas and how we may overcome these challenges. In future articles, we’ll introduce polyculture designs, plant lists, and best practices for growers with the ultimate aim being to provide a guide for designing, building and managing regenerative systems for this climate.
The series will include the following:
Part 1 - Introduction to Xeric Regions - Geographical Categories - Conditions and Challenges for growers in these regions and how to address them.
Part 2 - Xeric Forest Gardens - Multilayered Xeric Polyculture - Canopy, Shrub, Herb, and Ground Layers.
Part 3 - Building Soil - Biomass Plants, Producing Biomass, Composting, Manures.
Part 4 - Productive Polycultures - Home Forest Gardens - Commercial Growing, Edible Landscapes for Drylands.
Part 5 - Support and Fertility Polycultures - Xeric Nitrogen Fixers, Mineral Repositors, and Borg Plants.
Part 6 - Infrastructure Polycultures - Windbreaks, Hedging, and Amenity Planting.
Part 7 - Management - Irrigation, Harvesting, Pest Control, Pruning, and Fertility.
So, let’s get started with an overview of the xeric regions of our planet.
Introduction to Xeric Regions
The term "xeric" comes from the Greek word "xēros," meaning "dry," and is used in ecological and botanical contexts to describe environments or habitats that have very low moisture levels. Xeric conditions are typically found in deserts or arid regions, where plants and animals have adapted to survive with minimal water. The yellow areas in the map below do a good job of indicating where you will find these conditions on our planet.
Xeric regions are characterized by their dry climates, low rainfall, and arid conditions. The broad regions of the world typically considered xeric include:
Deserts
Sahara Desert (North Africa)
Arabian Desert (Middle East)
Kalahari Desert (Southern Africa)
Sonoran Desert (North America)
Mojave Desert (North America)
Atacama Desert (South America)
Gobi Desert (Central Asia)
Semi-arid Regions
Great Plains of West Kazakhstan
Great Plains (North America)
Central Asia (including parts of Kazakhstan and Mongolia)
Mediterranean Regions (areas with dry summers and wet winters)
Savannas
Some savanna regions, particularly those with long dry seasons, can also be classified as xeric.
Mountain Regions
Certain high-altitude areas can have xeric conditions due to rain shadow effects.
These regions are often characterized by specific flora and fauna adapted to low water availability. However, growing strategies and planting schemes that work in one place will not necessarily work in another. There are several variables to take into account that will determine which plants to use and the optimal practices to carry out.
Design Variables to Consider
Climate Variability: Different xeric regions have varying temperatures, humidity levels, and seasonal rainfall patterns. For example, the Sahara is much hotter than the Atacama Desert, and plants that survive in one place may not be hardy enough to survive in another.
Soil Types: Soil composition and nutrient availability can differ significantly. Some areas may have sandy soils, while others may have clay or rocky substrates, impacting water retention, pH, and fertility.
Local Flora and Fauna: Native plant species are adapted to specific conditions. One region's native plants may not be appropriate for another's and can, in rare cases, be invasive when introduced into new environments.
Water Availability: Access to water sources, such as underground aquifers or seasonal rivers, varies, affecting irrigation techniques and plant selection.
Pest and Disease Pressure: Different regions may have unique pests and diseases, requiring tailored management strategies and suitable species selection.
Practically Similar Xeric Regions of the World
Accounting for these variables, some regions share similar enough conditions that should allow for the same or similar polycultures to thrive. Here are some potential groupings:
Hot Deserts: The Sahel, a vast semi-arid region of Africa separating the Sahara Desert to the north and tropical savannas to the south. The Arabian Peninsula, Sonoran Desert, Mojave Desert.
Semi-arid Regions: Great Plains, Central Asia, Eastern Europe, Kazakhstan, Mongolia.
Mediterranean Regions: Mediterranean climates (parts of Southern Europe, California, and Australia).
Savannas: African savannas and parts of South America.
As mentioned above, it’s crucial to consider local soil, water availability, and pest pressures, and incorporating native species should always be a priority in regenerative polyculture designs.
For finer grain categorization and to locate areas that are climatically compatible, we can refer to the Köppen climate classification, where we will find the B classification indicating a hot desert climate.
These regions share hot desert climates characterized by low precipitation and high temperatures, especially in summer. Many areas have sandy or rocky soils with low organic matter, affecting water retention and nutrient availability. Water sources are often limited, leading to reliance on irrigation from aquifers or desalination in coastal areas.
Being a sun lover with a strong desire to escape the temperate winter, I’ve spent a lot of time in North Africa, the Levant, and the Arabian Peninsula over the last five winters, observing both the native plants in these regions and the cultivation practices. That said, I’ll be focusing the polyculture designs, plant lists, and practices for this climate zone, specifically centered around BWh: Hot desert climate, where B = Arid and semi-arid climate, W = Indicates a desert climate, and h = Hot, meaning the hottest month averages above 18°C.
Countries that have a significant area of land in this climate type include:
Saudi Arabia
United Arab Emirates
Qatar
Bahrain
Oman
Yemen
Egypt (parts of)
Jordan (parts of)
Kuwait
Iraq
Sudan
Libya
Iran (parts of)
Some mountainous regions in these areas may exhibit a more temperate climate, classified as Csa (Mediterranean climate), but the majority can be classified as desert and mostly subtropical, with the exception of Iran, which has a temperate climate in the north.
Although the focus will be on the BWh Köppen climate classification, there should be enough overlap to make the information in this series useful for growers in the following zones too:
BWk: Cold desert climate
BSh: Hot semi-arid climate
BSk: Cold semi-arid climate
Csa: Mediterranean hot-summer climate
Csb: Mediterranean warm-summer climate
Dfa/Dfb: Humid continental climates (warm/cool summer)
Dsa/Dsb: Continental climates with dry summers
If you are curious as to exactly which KCC zone you are located in, you can download a Google Earth overlay from here. I’d recommend the high-res download, although mid-res works well too.
Microclimate
Another factor to consider is microclimate, which includes exposure to wind, light, and water within a specific location. For example, the photo below is of a north-facing slope sheltered somewhat from salt-laden winds from the sea to the south and intense heat from the sun for a significant period of the day. In stark contrast to the south-facing slope on the other side of the valley, this slope is well-vegetated and home to a diversity of plants, insects, reptiles, and birds.
So now that we know the climate and regions of the planet we are focusing on, let’s look at the conditions, challenges, and potential solutions when growing in these regions.
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Typical Soil Conditions
Overview of Soil Formation
In temperate regions, soil is formed through the natural processes of rain, frost, plants, and microorganisms that break down rocks into fine particles, blending them with organic material from decaying vegetation. Conversely, in arid regions, this process is much slower, resulting in minimal natural soil and even less organic matter. The bedrock in these areas is often limestone, leading to alkaline soils that can inhibit plant growth. Additionally, salinity can pose challenges in some locations.
Enhancing Soil Quality
To improve the quality and depth of soil, especially in areas with poor natural soil, it is often necessary to import additional materials. Even established growing areas can benefit from the addition of organic matter. Before sourcing soil materials, it is essential to understand the present soil types and the ideal conditions for plant growth. Typically, the soils found in these regions include sandy and silty soils.
Sandy Soils
When natural material is present, it is most commonly sand. Sandy soils consist of large particles that allow for easy cultivation and excellent drainage, which many plants require, especially during humid periods when they are prone to rot.
Advantages:
Well-drained and easy to work with.
Disadvantages:
Lacks essential nutrients.
Nutrients are quickly washed away.
Dries out rapidly and requires frequent irrigation and feeding.
Fine Silty Soils
Fine silty soils, often sourced from wadi basins and recharge dams, are commonly referred to as "wadi soil." They consist of very fine particles that form a solid mass, allowing for significant water retention.
Advantages:
Excellent water-holding capacity.
Disadvantages:
Becomes slimy and unmanageable when saturated.
Forms hard lumps when dried.
Lacks air spaces, creating a challenging environment for root respiration.
Water cannot penetrate easily, resulting in surface pooling while lower layers remain dry.
Neither silt nor sand is ideal, but a mix of the two, creating loamy soil, makes a good medium for plant growth. The mix of particle sizes holds water better than sand while allowing better aeration and drainage than silt.
The Importance of Organic Material
Incorporating organic material into the soil offers numerous benefits and serves as a fundamental solution to various soil issues across all climates. Organic matter can take many forms, including peat, compost, tree bark, coconut fiber, animal manure, and homemade compost. It acts as a soil conditioner, enhancing moisture retention while preventing waterlogging.
Rich in beneficial soil bacteria, organic material breaks down micronutrients into simpler forms that plants can easily absorb, which are essential for healthy growth. Its mildly acidic nature also helps to counterbalance the typically high alkaline levels often found in the soils of this region.
Certain types of organic material, such as animal manure, not only improve soil structure but also enrich it with essential nutrients. In contrast, peat serves primarily as a conditioner, though it is low in nutrient content.
The high temperatures of the region accelerate the decomposition of organic material by soil bacteria, leading to significant breakdown within six months to a year. As a result, it is crucial to regularly replenish organic matter in the soil. Throughout this series, we will delve deeper into these concepts, exploring strategies and polycultures designed to enhance biomass growth.
Soil Mixes Commonly Used by Landscapers
The following soil mixes are used by landscapers in this region and will vary depending on how much drainage is required and how much fertility needs to be provided. Generally speaking, the more organic material in the mix, the better.
80% Sand - 20% Organic matter
80% Sand - 10% Organic matter - 10% Vermiculite/Perlite
50% Sand - 20% Organic matter - 30% Wadi soil
Common Soil Problems
The soil issues typical for these regions are alkalinity, salinity, and hardpan.
Soil Alkalinity
Soil acidity and alkalinity are measured on a pH scale that ranges from 0 to 14. A pH above 7 indicates alkaline soil, while a pH below 6.5 is considered acidic. The optimal pH level for plant growth lies between 6.5 and 7, which is neutral to slightly acidic.
Soil pH is influenced by the underlying bedrock, with limestone being prevalent in many regions, leading to generally alkaline soils. High alkalinity can hinder plants from absorbing essential nutrients, particularly iron and magnesium, leading to poor growth and a condition known as chlorosis. Symptoms of chlorosis include dark green mid-ribs and veins, with the rest of the leaf appearing pale.
Fortunately, this issue can be addressed by incorporating organic matter into the soil, which helps to increase acidity and improve nutrient availability for plants.
Soil Salinity
Salts are a natural component of all soils. In areas with sufficient rainfall, these salts dissolve and are washed away into streams and the sea. However, in arid regions or areas without a direct drainage route to the ocean, some of this water evaporates, leading to a concentration of dissolved salts. This process can result in the formation of salt lakes, brackish groundwater, salinized soil, or salt deposits.
High salinity levels can significantly hinder plant growth. Affected plants often display small, pale leaves, and in severe cases, leaf edges may brown, ultimately leading to plant death. While some plants may continue to survive, they often remain stunted and poorly developed. If you notice poor plant growth despite good soils and adequate irrigation, it’s probably saline soil, and it’s a good idea to test the soil for salinity.
To mitigate salinity, salts can be leached from the soil through ample application of fresh water, provided that drainage is adequate and water is available. Another option is to incorporate compost and cultivate plants in free-draining raised beds. However, salinity issues can often recur in the long term. A more effective approach may be to grow tougher, salt-tolerant plants, of which there is a wide variety, while more sensitive species can be cultivated in containers.
Here is a list of plants that will thrive in saline conditions and suitable for this region. In future articles, we will explore more closely specific plants and polycultures and examine the general salt tolerance levels of various species.
Hardpan
A hardpan can often be found in areas where fine silts have been washed in, settled, and baked hard in the heat. The result is a layer of dense, impermeable material that forms below the soil surface and inhibits water drainage, leading to localized waterlogging and creating a barrier for plant roots.
To alleviate hardpans, they can be manually broken up using a pickaxe, or for larger areas, various plowing implements attached to a tractor can be employed. Once the hardpan is disturbed, it is essential to continuously add organic matter to the surface, such as maintaining a mulch layer and providing shade through growing plants. This will help prevent the hardpan from re-forming. Additionally, well-designed earthworks and effective site grading that channels rainwater runoff can minimize sediment accumulation and reduce the formation of hardpans in the first place.
Animal Browsing and Fencing
As anyone who has visited this part of the world will know, there is lots of land, with the majority of it open to explore for humans and other animals, including camels, goats, and sheep. Fencing should certainly be considered before planting out. We’ll look at various fencing options later in the series.
Xerophytic Plants
The climate naturally supports xerophytic, drought-tolerant shrubs and grasses, with some small areas of dry tropical scrub and thorn forest. We’ll be looking closely at these plants throughout the series, with a special interest in food and medicinal plants, nitrogen fixers, mineral repositors, and biomass plants.
Native flora is ideally suited to the environment and benefits the wider ecosystem by being a host to native insects and birds. Native plants are not yet widely available in the nurseries of the region, but many of the species featured in this series are easy to grow from seed. These plants want to grow in this climate and need no assistance. Once established, native plants need very little water to thrive and are a long-term contribution to the environment.
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Other Challenges of Growing in Xeric Regions
Growing in xeric regions presents several significant challenges, primarily stemming from the inherent aridity of these environments. Obviously the most pressing challenge will be the lack of water and other challenges include:
High Evaporation Rates: The combination of high temperatures and low humidity can lead to rapid evaporation of soil moisture, further exacerbating water scarcity.
Limited Biodiversity: The harsh conditions often result in lower biodiversity, which can disrupt ecosystems and make them more vulnerable to pests and diseases. This reduced diversity can also negatively impact pollination and fertilization rates.
Temperature Extremes: These areas frequently experience extreme heat, particularly during the summer months. Such conditions can stress plants and lead to decreased yields. Additionally, significant temperature fluctuations between day and night, especially in desert regions classified as BWh, can further challenge plant survival. For example, daytime temperatures may soar, while nighttime temperatures can drop considerably. Weather patterns can also introduce occasional temperature spikes or drops, particularly during transitional seasons. The Khareef in South Oman and Yemen exemplifies this phenomenon.
Soil Degradation: Soils in xeric regions may be low in organic matter and nutrients, suffering from erosion or salinization, which adversely affects fertility. Limited vegetation cover can lead to increased soil erosion, particularly in windy conditions, further degrading soil quality.
Limited Crop Variety: The harsh conditions restrict the types of crops that can be cultivated, often confining growers to drought-tolerant species.
Plant Adaptation: When planting nursery plants, there may be a need for time to develop specific adaptations, such as light and heat tolerance, deeper root systems, or drought-resistant features. This process can be time-consuming and may not always yield successful results. Utilizing native plants, local cultivars, and sourcing plants from nurseries that cultivate them under field conditions—rather than the pampered conditions of industrial nurseries—may enhance success rates.
Economic Viability: The combination of lower yields and high input costs, particularly when utilizing desalinated water, can pose economic challenges for commercial agriculture in these regions. However, with an increasing number of developments from both public and private sectors and significant budgets allocated for grounds maintenance, introducing xeric polyculture appears feasible. This approach is likely to result in reduced costs and healthier plants and ecosystems.
Positives of Growing in Xeric Regions
While there are endless reasons to garden anywhere on our beautiful planet, the unique conditions in arid areas can really make a difference with some smart growing techniques.
Visual Appeal - In those hot, dry spots, the bright green of plants really pops against the landscape. Just a few strategically placed plants can create a stunning visual effect that brightens up the surroundings.
Long Growing Season - Xeric regions usually have long growing seasons. With a bit of irrigation, you can have something blooming or fruiting throughout the year.
Fast Growth - Many plants in this region grow surprisingly quickly. Some shrubs and trees can reach impressive sizes in just a year and with all that sunshine, you can create productive, layered gardens that maximize your space.
Focused Plant Choices - While there may be fewer plant options compared to other places, this makes it easier to really get to know the plants you’re working with. You can dive into the 2,000 to 3,000 native species, like different grasses, shrubs, and trees, many of which are perfectly suited for the dry conditions and are often overlooked.
All in all, growing in xeric regions not only brightens up the landscape but also supports local wildlife and encourages sustainable practices. By embracing the quirks of these areas, you can make a real impact and enjoy the journey along the way!
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See you next time for Part 2 - Xeric Forest Gardens - where we’ll cover multilayered xeric polycultures and look at species for Canopy, Shrub, Herb, and Ground Layers.
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