Perennial Plants and Permaculture


Currently, approximately 80% of the food crops grown in the world are annual plants, and it’s been this way for quite some time. Perennial plant food crops are pretty much in the minority in terms of how the human race derives its nutrition.

Permaculture strongly emphasises the importance of using perennial plants in our food production systems. When we consider the permanent agriculture aspect of permaculture, it should be apparent that we would need to utilise perennial plants to construct a permanent system,  rather than using  annual crops to create temporary systems, which are there one season, and return to bare earth the next.

The preference for perennial plants is stated explicitly in the seventh permaculture design principle — Small Scale Intensive Systems. It describes the use of perennial plants instead of annual plants as one of the features that differentiates permaculture small scale intensive systems from either conventional commercial or peasant farming systems.

To many people, the reason we use perennial plants is simply because they don’t need to be replanted each year, and don’t die down each year, saving us a lot of effort digging, sowing seeds, and cleaning up at the end of the season — and then they simply leave their understanding at that.

There are in fact far more profound ecological and environmental reasons for using perennials rather than annuals in our food production systems, which we will explore in this article.

Before we can understand the larger scale impacts of using these two broad categories of plants, it is important that we first understand their biology, so that we can comprehend precisely how they function in a living ecosystem.

Annual vs. Perennial Plants

All living organisms evolve a unique strategy for survival and reproduction, and they adapt themselves to best function in their specific environments. When we examine the biology of annual and perennial plants, we observe that they have evolved two very distinct survival strategies, and as a result, they occupy very different ecological niches.

Annual plants are short lived plants, living only for a year. They flower, produce seed at the end of this cycle, and then die down. This group includes ‘weeds’, vegetables and many flowers — both wild and cultivated.

Their survival/reproduction strategy can best be described as “live fast and die young”. Annuals reproduce from seed, and grow very quickly compared to perennials. To do this, they require very large amounts of available soil nutrients to support their rapid growth rates.

The reason they are in such a hurry is because they need to mature as fast as possible and produce large quantities of seed within the same year, before they die down. Producing large quantities of seed is a specific survival strategy, it increases the chances of seeds germinating and producing new plants. This very fast growth pattern does not allow the plant much time to establish itself. It is an all out effort to get to the seeding stage before their growing season ends.

In fitting with this growth strategy, annual plants have very shallow roots. Annual vegetables usually have the majority of their root mass in the first 6” (15cm) of soil. A few longer unbranched roots will extend deeper, up to 3-4 feet (90-120cm) but these only form a tiny percentage of the overall root mass. This is why you can grow almost any annual vegetables in fairly shallow garden beds and containers around 40-50cm deep.

The important points to note with annuals are as follows:

  • When these shallow rooted annuals are watered, as the water seeps deeper into the soil, they are unable to access it.
  • Any nutrients that lie deeper in the soil are inaccessible to them because their roots do not reach deep enough.
  • Annuals do not form permanent ecosystems because they are temporary plants, once they reach the end of their growing season, they produce seed, and then die down leaving bare soil.
  • Since they are short lived, their root networks can only temporarily stabilise the soil to prevent soil erosion.

If you look at a backyard vegetable garden or a commercial farm covering hundreds of acres of land, annual food production works exactly the same way. Seeds or seedlings are planted, they grow very fast after being given huge amounts of fertiliser, they are harvested, the soil becomes bare again, then next year they are replanted once again, and the cycle runs indefinitely. To prevent localised nutrient deficiencies and plant-specific diseases, the practice of crop rotation is used, where a specific type of plant, say carrots, are planted in a different garden bed each year, and a different vegetable is planted where the carrots once were, for example.

Perennial plants on the other hand have a very different survival and reproduction strategy. They are long-lived plants, and can live from many years to many centuries, depending on the species. This group includes herbaceous plants (which have green stems with no wood in them, such as many herbs) and woody plants (such as woody shrubs, vines and trees). These plants can reproduce from various types of offshoots from a parent plant, or they can reproduce from seed just like annuals, or in both ways, once again depending on the species.

Perennials grow quite slowly in comparison to annuals, as they take their time to establish themselves, putting out extensive root systems very deep into the soil, which allows them to access water and nutrients that cannot be reached by annual plants. They create a permanent network of roots that help stabilise the soil and prevent erosion.

Perennial plants have very deep roots. Perennial vegetables such as artichokes and asparagus have roots that extend much deeper than 4 feet (120cm), far deeper than annual vegetables, and tree roots can run as deep as the height of the tree itself. The deepest recorded depth that tree roots can run is 60m. The advantage that perennials have with such deep running roots is that they can access water and nutrients that are beyond the range and reach of annual plants, making them far better adapted to extreme conditions. The very long perennial root systems are also excellent at stabilising steep slopes and river banks, which shallow rooted plants are unable to do.

Growing relatively slowly, perennials do not need large quantities of nutrients like annuals do to grow. They use a small amount of nutrients from the soil over a longer period of time, and as such are much better adapted than annuals to grow in low nutrient environments. In warmer climates, perennials can grow continually, while in colder climates they become dormant in winter and stop growing, then resume growth when the winter passes. So, they are able to commence growth earlier than annuals can, because they are an already fully established plant, whereas an annual has to start from scratch as a tiny seedling.

The important points to note with perennials are as follows:

  • In Nature, most of the plants on the planet are perennials! The majority of all terrestrial (land based) and freshwater aquatic plants are perennial plants.
  • Being long lived plants, perennial plants create stable ecosystems such as forests, which can provide a food source and a home for a diverse range of flora and fauna. Forests are home to approximately 50-90% of all the world’s terrestrial biodiversity. Tropical forests alone are estimated to contain between 10-50 million species — over 50% of species on the planet. Annual farmlands are only a temporary home to pest insects, nothing else.
  • Perennial plants don’t need to be replanted every year, so the arduous, energy intensive and equally energy inefficient seasonal task of ploughing, digging and sowing seed that is carried out for annual crops is no longer a concern.
  • Deep roots and a slow growth habit means that less fertiliser and water are required to grow perennial plants, and they are on the whole a lot more productive than annuals.
  • Growing perennial food plants is a far more sustainable and energy efficient, and requires much less work overall.

Now that we have looked at the unique attributes of annual and perennial plants, we can now examine the larger scale impacts of using each of these as our predominant plant group in our food production systems.

The Problem with Annual Food Production Systems

As mentioned in the introduction, in agriculture on a world-scale, over 80% of all crops farmed are annuals, whereas in Nature, over 90% of plants are perennials. From this simple fact it is clearly evident that our conventional farming systems are very far removed from how Nature prefers to grow plants. Most people are unaware that annual food production systems are very unnatural and unsustainable systems — annual monocultures even more so! They are human concepts, and yet we wonder why they don’t really work properly…..

One of the big problems with annual crop agriculture is that the annual plants are heavy feeders, and need large amounts of fertiliser, often during the growing season. Being shallow rooted, they need frequent irrigation too, to stop them drying out. Shortly after they are irrigated, the water naturally seeps downwards into the soil, out of range of their shallow roots, so they can no longer access it. This water gradually percolates deeper into the soil, carrying all the dissolved nutrients with it, permanently out of reach of the annual plants.

Without any deep roots of perennial plants to intercept this excess water and take it up, it will end up in waterways or the water table.

Contamination of Waterways

Water always flows to the lowest point, and if this nutrient-rich water eventually reaches waterways such as lakes, creeks or rivers, the massive dose of nutrients (usually mixed with synthetic chemical pesticides and herbicides, but that’s another story) causes destruction of these ecosystems by eutrophication — the excessive nutrients create a massive increase in the growth of algae in the water, which consumes all the oxygen and suffocates all the aerobic life in the ecosystem. On top of this we have the pesticide and herbicide washed off in surface runoff from farms which compounds the problem, causing both acute and cumulative poisoning of the whole aquatic ecosystem and surrounding environment.

Algal bloom in village river, Sichuan, China – Felix Andrews

Increased Water Table Levels

The other path for this nutrient laced irrigation water is straight down, into the water table beneath the ground, where it causes the level of the water table to rise. As the water table levels rise up into the soil, they bring up dissolved salts, causing salinity in the soil. When salt rises in the soil, the ground is destroyed, laid barren, and nothing can grow there. When perennials with their deep roots are present, especially trees, they can draw water from deep below the surface, and transpire it into the air, keeping the water table down. When the trees are all felled and cleared, to create a field — which is where the word comes from — there are no plants in an annual farmland that are capable of reversing the rising of the water table and remediating the situation, so all is lost.

Salt-affected soils in Colorado – public domain image.

Once the soil succumbs to salinity, all plant life is killed off, and then the soil is subject to erosion. The top soil is blown away by wind and washed away by rain, leaving a barren, sterile, salty wasteland. One of the solutions employed in restoring this damaged land is to plant salt-tolerant trees to reduce the water table levels. Other solutions are centred around costly engineering solutions to ensure that rural water catchments such as dams and irrigation channels don’t ‘leak’ water in ways which mobilises salt.

Even without irrigation, the removal of native vegetation alone to clear space for annual crops is enough to cause another form of soil salinity, dryland salinity.

Dryland Salinity

In non-irrigated land, where there is only rainfall supplying water, dryland salinity is caused by by clearing deep rooted perennial vegetation and replacing it with shallow rooted annual plants. This causes the water table to rise, because rainfall not used by plants either simply runs off the soil surface, or infiltrates beyond the root zone of the shallow rooted annuals, and accumulates as groundwater to create the problem.

There are no secrets about the cause here either, to cite the Australian Government’s Department of Sustainability, Environment, Water, Population and Communities web site on the topic of “Salinity”:

Increasing salinity is one of the most significant environmental problems facing Australia. While salt is naturally present in many of our landscapes, European farming practices which replaced native vegetation with shallow-rooted crops and pastures have caused a marked increase in the expression of salinity in our land and water resources.

Rising groundwater levels, caused by these farming practices, are bringing with them dissolved salts which were stored in the ground for millennia. Salt is being transported to the root-zones of remnant vegetation, crops, pastures, and directly into our wetlands, streams and river systems. The rising water tables are also affecting our rural infrastructure including buildings, roads, pipes and underground cables. Salinity and rising water tables incur significant and costly impacts. — Australian Department of Sustainability, Environment, Water, Population and Communities

So, how big a problem is this?

  • According to a 2000 report by the Food and Agriculture Organization of the United Nations, the total global area of salt-affected soils was 8.31 million square kilometres, affecting  every continent except Antarctica.
  • It is estimated that about 15% of the total land area of the world has been degraded by soil erosion and physical and chemical degradation, including soil salinization (Wild A. 2003. Soils, land and food: managing the land during the twenty-first century. Cambridge, UK: Cambridge University Press).

Decreasing productive land and an increasing population is a sure recipe for food shortages.

In a continent such as Australia, where salinity is a major threat, some scientists are trying to deflect the blame on traditional agricultural practices by insisting that removal of trees is a secondary cause, not a primary one, and that the primary cause was a 100 year cycle of increased rainfall — which ended in 2000, that caused salinity issues in the 70s and 80s. This in my opinion is a nonsensical argument as Nature is self-regulating and the landscape will support more plants and trees during long term cycles of increased rainfall, which would naturally reduce the water table level, and prevent any salinity problems. If it were not the case, we would have a recorded history of salinity in virgin bushland every one hundred years, which is not the case. The removal of perennials to create annual crop food production systems is the cause of salinity, it is a man-made problem, as confirmed in the quote by the Australian government itself.

In Summary

Through the extensive use of annual crop-based agriculture, we are systematically destroying living ecosystems which support many living organisms, flora and fauna, and replacing them with artificial systems composed solely of annuals, which cannot exist naturally in this state without excessive inputs of energy. The end result is that we are also destroying the soil as a consequence, losing it to salinity and erosion, at a time when the planet’s demand for arable soil for food production is increasing due to population growth. By decreasing the usable land and increasing food production, we are exponentially increasing the demands on the planet, pushing it to breaking point at an ever increasing rate.

And all because we want to farm annuals exclusively….

That, in a nutshell, is why we prefer to use perennial plants in permaculture systems rather than annuals.