|Plant communities and natural pest control|
A derelict urban plot covered with weeds and young trees is a highly naturalistic garden - nature has quickly reclaimed this open space. We will see many native species there (a few may dominate) and possibly something exotic, like a butterfly bush (Buddleia) whose seed has blown in with the rest. We will also see that this garden harbours wildlife, from the ground living insects through to the flying visitors. Because it is neglected, wildlife will feel undisturbed and safe, and so a natural balance can develop between prey and predators.
This natural balance has sustained life over millions of years, helping to ensure that plantlife is never wiped out and that the cycles of life continue. It has many lessons for us in building our own gardens and in the success of growing food. We can use nature’s balance to help with our pest control since the pests are often the prey of the predators. Pests, unfortunately, will always visit our garden, but we must make an effort to attract the predators in and give them a reason to stay.
In the simplest of terms, we can bring predator insects in to our garden by attracting them with flowering plants. Insect predators are attracted to flowers because they can get nectar from them. Having drunk the nectar, these beneficial insects may stay around and look for more food such as a few pest insects. If the pests are abundant, such as the soft-bodied aphids, they may decide to breed, laying their eggs on the underside of leaves near the pests. Once the eggs have hatched out, the pests are a nurturing supply of food for the predator’s highly mobile larvae.
The larvae, especially of insects like the ladybird, hoverfly and lacewing, are probably as voracious eaters of pests as the adults. We can therefore bring these predator larvae right in to where we are growing our vegetables by planting flowers that provide nectar as companions to the vegetables. The companion plants are freely flowering annuals that can be sown directly where you want them to grow if you have a light, warm soil. For the rest of us it is probably better to multi-sow them in modules and plant these clumps out around the edges of vegetable beds, and in amongst the larger vegetables (cabbage family, courgettes and marrows). Try sowing limnanthes (poached egg plant) calendula (pot marigold) borage, echium, annual convolvulus and nasturtium. You can also use pots or planters for your companion plants, moving them into position by the vegetable beds and next to where you need them most.
Over the years, the companion plants can be left to seed and will build up a seedbank in your beds. The task then of separately sowing companions gets less each year and you may have to do a bit of weeding to make space for your vegetables. In the long run, you should think about designing your growing area to have a few small-scale permanent beds for pest predator attracting, where you make use of perennial plants rather than annuals. This will save on work and probably provide a habitat where the predator insects can find shelter over the winter, therefore staying put in your garden. More of this later, after we have looked at a bit of our gardening history.
Richard Bird1 describes in his book on companion planting how this technique was key in the development of the cottage garden. The cottage garden style arose from the need of working folk (who had limited access to land) to grow a varied range of plants in the same space. Thus they mixed the ornamental with the productive - the flowers with the vegetables. The techniques they used grew from experimentation, with the experience being handed down from generation to generation. Because of a lack of time available for gardening, the flowering plants had to be easy to maintain and have a long period of interest. So plants were chosen that got on well with each other, and which provided all season interest through colour, shape, texture and even fragrance. Many of the flowers had uses as culinary and medicinal herbs and as dye plants. As important was that they created inviting habitats, drawing in pest predators that would develop a natural balance and reduce the damage to the productive plants.
By day the cottage gardeners probably worked in the fields, using a system of growing that was totally different to their own garden. The invention of the horse-drawn seed drill had seen efficiencies helpful to farmers. But it has meant that fashion changed over the last few hundred years and that home-growers went on to ape the broadscale agriculture that they saw, thinking that vegetables can only be grown in straight lines. So says the late Geoff Hamilton2 who had a fine eye for the absurd and a tremendous feel for what was beautiful and natural. He recognised that the field hoe and seed drill were the driving force for agriculture to turn into the monoculture that we see today. Farmers before that used to broadcast their seed in random fashion, throwing over one shoulder and then the next to create blocks, almost as if the plant was dispersing the seed and getting help from the wind in doing so. The seed stock wasn’t always clean and so arable flowering weeds were dispersed and grew at the same time, creating the colourful field mixes that we rarely see today. Those of you who have seen the video of Sepp Holzer's Austrian farm3, will recognise his deliberate use of mixed seed broadcasting to create the plant communities that grow his food and maintain his soil.
Where is the danger with straight rows of the same crop? Well, a field full of cabbages sends out a big message to every pest in the district to come along for a feast. While the cottage gardeners may not have appreciated it, their method of mixing plants together (companion planting) provided a natural means of pest control. Partly it was the hiding away of vegetables amongst the camouflage of other plants, but it was also the natural balance that was created through the attraction of pest predators. The dispersal of vegetables amongst other plants has another advantage in that it lessens the chances of diseases gaining a foothold.
Geoff Hamilton took the idea of the cottage garden one step further. While native plants are always recommended by naturalists as a draw for wildlife, Geoff recognised that his ornamental gardens didn’t lack for insects or birds. This made him think that he didn’t have to limit himself to native species. Moreover, ornamental plants and vegetables were his twin passions and he couldn’t see why he shouldn’t mix the two together in a creative design, rather than what usually happened, with the vegetables hidden away at the bottom of the garden. Thus he developed the idea of the ornamental kitchen garden which he shared with us in his book4 and TV series. Here was the planting of a backbone of perennial plants that gave ornament, scent and some productivity, but which also provided habitat for pest predators. Into this were planted the annual vegetables, some in small beds within the backbone and some inter-planted amongst the perennials. His philosophy on pest control was thus - when asked how to combat aphids on rosebuds, Geoff advised the questioner to sit on his hands! Geoff knew that the best way of tackling pest control in our gardens was to let nature get on with it, providing of course that we had given an invitation to nature to come in and get on with the job.
Companion planting annual flowers around vegetables, cottage gardens and ornamental kitchen gardens all demonstrate the use of plant combinations and communities for pest control suitable for the smaller garden. In larger spaces, such as orchards, habitat enhancement has long been used, such as the wildflower strips that can be seen in amongst the fruit trees at Ryton Gardens near Coventry. These wildlife refuges (or bug banks) are formed by leaving strips of the orchard turf unmown and supplementing the plant community by seeding in flowers like field poppy, ox-eye daisy and yarrow. As well as their role in pest control, they will of course attract pollinating insects useful for fruit set in orchards. In broadscale agriculture, these bug banks have been made by sowing up strips at the edges of fields with native wild flowers (you can use a mix of natives and exotics in your garden if you want). The bug bank strips are left undisturbed, allowing the pest predator insects to roam into the fields looking for pests and thus their food. Examples of these can be seen at Elm Farm Research Centre in Hamstead Marshall, near Newbury. Other trials have used seasonal bug bank strips spaced throughout an arable field. Established each year by sowing, they are ploughed under at end of season allowing a transient but flexible system.
Permaculture has plant combinations and communities at the centre of its land use. The obvious example is the guild, described by Mollison5 as a harmonious assembly of plant species (but it could be plants and animals). The essential characteristic of a plant guild is a diverse mix (polyculture) whose elements all have a purpose and which are beneficial to each other, and so it is similar to the thinking behind companion planting. The design of guilds, and the choice of plants, makes use of the advantages that the natural world provides, such as below ground in the beneficial symbiosis with nitrogen fixing bacteria and mycorrhizal fungi, and in the property of dynamic accumulation of minerals. Above ground are the flowers and berries that attract insects and birds - our natural allies in pest control. The physical structure of the guild may allow it to provide shelter from winds and frost. And it may also throw shade that serves the purpose of creating another microhabitat.
Guilds can be constructed by use of annual plants, but self-seeding tends to allow creep (see above in the explanation of companion planting of vegetables). Thus it is best to have a permanent plant community using perennial plants that stay put, somewhat as in the ornamental kitchen garden. When planting guilds, experimentation and experience (observation) will tell us if it works. Plant choices can be made on their range of property and function, but they should also be made on the particular characteristic of growth of the plant. For instance, does it crowd out its neighbours by spreading aggressively? Does it expand by forming clumps, or does it spread by underground shoots or through producing a carpeting groundcover? Is it stable and long lasting?
Peter Thompson6 provides some explanation of this approach by describing a community of plants as being a matrix of successive layers of vegetation above ground and a similar complex pattern of roots below ground (i.e. some plants have spreading roots, some have deep tap roots and others have a mat of roots in a clump). Creating a plant matrix requires the ability to match plants with the habitat (i.e. soil, climate, shade etc.) and to create plant alliances that make use of the ability of plants to form mutually dependant groups. The closeness of planting and the eventual growing together of the different plants means that there is rarely any bare soil, thus keeping unwanted weeds out. This reduces work, as there is no hoeing, little ground preparation, and little need for external inputs. Because the plants form a cover, they will reduce water loss from the soil and thus the need for watering. The plants and the communities they form become the controlling factor, feeding back what if any work should be done.
Establishment of a guild takes time and the character and composition of any planting changes as it develops and matures. Annuals and short-lived perennials can sometimes be used as fillers in the early stages, dying back or being crowded out within a few years. A woodland edge could be thought of as being the most completely developed guild. A micro-forest can be made by mixing shrubs and small trees with perennials in a mixed guild. The shrubs emerge like islands from the perennials, with the trees forming vertical accents above. While we may think of a matrix as being three-dimensional, there is another dimension to consider and that is season, with different plants contributing to the matrix at different times of the year.
I have experimented with two different types of guild in my garden and wherever I happen to be teaching or garden building. Each attempts to show the integration of different plant types: Why should herbs be grown just in an herb garden, or top fruit and soft fruit all on its own? Is there a way of making pest control part of the permanent infrastructure of a vegetable garden or even amongst fruit? Here are descriptions of those guilds.
Linear guilds comprised of narrow beds of herbaceous perennials can be spaced throughout a growing area (there are usually two perennial beds for every six vegetable beds). The planting of the perennial beds is carried out with a number of aims in mind. First, they should attract pest predator insects, so that the beds become bug banks. Next, it makes sense to grow green cuttable mulch material right next to the vegetable beds where it is to be used (i.e. perennial nitrogen-fixers such as clover and lucerne, and the dynamic accumulating comfries). Then these narrow beds are a chance to grow herbs (both culinary and medicinal) and the few perennial vegetables available to us, giving some additional produce. Lastly, in many cases the linear beds provide wind diffusion (wind breaking) improving the climate throughout the growing area. Straight-line (linear) guilds aren’t essential – these type of herbaceous perennial guilds can be any shape and size as long as they are designed smoothly into the infrastructure of the growing area.
The second type of guild incorporates woody plants and either stands alone - as an island - or is part of a larger area of woody planting such as an orchard or forest garden. The characteristic of these guilds is a triangular planting, with one point of the triangle being a top-fruiting tree (apple, pear, plum, cherry, crab apple or june berry) and the other two points being fruit bushes (blackcurrant, gooseberry, worcesterberry etc.). The space around and within the triangle is then planted with many of the same perennials that are used in the linear guild. There may also be other woody plantings incorporated (such as flowering currant, willow, sea buckthorn or alder) but these will be placed to the northern side of the guild so that they do not block out sunlight. Their purpose would be as early flowering shrubs that attract pollinating insects or that fix nitrogen. They are likely to be managed by coppicing or pollarding.
The woody guilds are oases of mixed plantings that have similarities to a forest edge garden. The top fruit give height and form the canopy. The fruit bushes, coppiced willow, alder and flowering currant are a middle storey, and the understorey or groundcover is made up from culinary and medicinal herbs, perennial flowers for pest predator attraction, and some perennial food. They also provide fertility for free from nitrogen fixers, mycorrhizal associations and dynamic accumulators. Spatially link these woody guilds with a kitchen garden or a suitably designed annual vegetable growing area and you begin to see an ideal for humanscale food production. But it is more than just about food production – its about an appreciation of all the plants we can grow, how they interact with themselves and the soil, and how they make our gardens attractive and inviting to all the visitors we want to share with us our own little part of the natural world.
Mark Fisher, 7 June 2002
1. Companion Planting, Richard Bird, Headline, 1990
2. Cottage Gardens, Geoff Hamilton, BBC, 19954. The Ornamental Kitchen Garden, Geoff Hamilton, BBC, 1990
3. Farming With Nature: A Case Study of Successful Temperate Permaculture, Crystal Lake Video, 20015. Permaculture – a Designer’s Manual, Bill Mollison, Tagari, 1988
4. The Ornamental Kitchen Garden, Geoff Hamilton, BBC, 1990
5. Permaculture – a Designer’s Manual, Bill Mollison, Tagari, 1988
6. The Self-Sustaining Garden - A gardeners guide to matrix planting, Peter Thompson, Batsford, 1997