Plants come in two main types: annuals and perennials (with the honorable exception of a few plants that last two years, called biennials). Annuals are species that go through their entire life cycle, from germination through to maturity and crop production within a single year. Having produced its crop, the plant then dies. Perennials, on the other hand, live for several years. They bloom, crop and die back over the course of a year, but the rootstock remains and it is from this, rather than a new seed, that the next year’s flowers and crops come. Fruit trees are an obvious example of a perennial plant that a permaculture gardener would consider incorporating into their design, but there are also many varieties of perennial vegetables.
The vast majority of crops in commercial agricultural systems are annual crops (and this, combined with the propensity for monocultures causes many problems for the soil and the ecosystem), but permaculture favors the perennial, primarily because of their established root systems. There are several advantages to growing perennials on your site, primarily related to the root systems of the plants.
Because they remain in the soil and grow over successive years, the root systems of perennial plants help to improve the structure of the soil. As they grow and spread out they create channels and spaces through which water can percolate, as well as pore spaces for aeration of the soil to occur. This benefits all the plants in the area, as well as the microorganisms in the soil, giving them the oxygen and water they need to survive, and routes through the soil to enable them to process more organic matter.
With deeper root systems that stretch further down into the soil, perennials are able to access nutrients out of the reach of annual plants. They then bring these nutrients up to the surface where they and other plants can access it. This is particularly useful for elements such as nitrogen, which is essential for plant growth, that plants need a lot of. It is also important for trace elements, such as magnesium and iron that tend to lie further down in the soil profile, rather than in the topsoil.
As well as bringing up nutrients from further down in the soil profile, the root systems of perennial plants are also able to draw moisture up. Again, this moisture becomes available in the upper levels of the soil for other, shallower rooting, plants to access. This also helps to prevent the soil from drying out and then becoming susceptible to erosion by the wind.
Planting perennials not only helps access more water from the soil, it also preserves soil moisture because the soil is at no point left exposed. While they typically die back in the winter, perennials do not lose all their foliage, retaining enough to effectively become a cover crop. This cover helps to protect the soil from evaporation by the sun. It also assists in maintaining soil structure as it protects from erosion by wind and rainfall. Such preservation of the valuable topsoil over the winter months makes nutrients available for plants growth
Because the perennial grows its crop from the same rootstock, the permaculture gardener does not have to expend energy clearing areas for sowing, sowing seeds and composting and mulching the soil to supply nutrients for plantings. Furthermore, the gardener can be reasonably sure about the quality and amount of the crop that the perennial will generate, at least during the plant’s mature years. This allows the individual to plan ahead for a glut – perhaps by preserving the excess fruit or vegetable or making a product to sell at the local market – and to know when their crop is likely to be ready to harvest. Perennials also tend to need less care than annuals, given that they are established and their rooting system helps give them the nutrients they need.
Many species of perennial plants live a long time, but even those will eventually begin to decline. Fortunately, perennials readily lend themselves to the propagation method of dividing. This involves digging up the root clump of the plant and splitting it into two or more separate plants. The permaculture gardener can then plant each division – ensuring they each have an area as large as that occupied by the plant from which they originated – and they will become new, viable plants, replete with renewed vigor and growing potential.
Annual plants all tend to bloom during the same period, typically the summer. Perennials have greater variety and so more various blooming times. By planning your perennial planting, you can ensure different crops become available at different times, extending the productive season of your plot, and giving you access to a wide variety of produce. Perennials are also generally hardier than annuals and so are more likely to survive extreme weather events, and produce a crop even if climatic conditions are not ideal.
When planting perennials it is advisable to include a good amount or organic compost. This helps the plant get established in the location they will occupy for several years. After they are established, they tend not to need much compost, but will benefit from mulching during the summer when they are growing, so as to preserve as much valuable moisture as possible.
Of course, annuals certainly have a place in a permaculture plot, not least because many tasty fruits and vegetables are annual plants. These include crops like carrots, celery and parsley. Cultivating solely perennial plants would deprive us of these nutritious and delicious crops, and others like them. However, planting annuals should be planned for, so that the earth is not left bare after harvest. Work on ideas for succession planting or utilizing ground cover crops that will be slashed for mulch. You may also want to plant a leguminous crop to help increase the amount of nitrogen in the soil, ready for another annual crop or a planting of perennials.