Close encounters among the plant kind: proliferating plant companions

When I was a child, my grandfather grew intoxicatingly fragrant rose bushes, spaced one metre apart. I would follow him around the garden as he potted about. He carefully maintained a surface of crumbly, bare soil underneath the bushes, with a very neat straight border between the bare soil and the thick grass. He believed this was good for both the soil and the plants. Such practices reflected conventional wisdom at the time.

Today, there is a growing understanding that soil needs protection, especially in the hot and dry climates of much of Australia. Bare soil exposed to sunlight will oxidise carbon, declining in fertility and becoming more vulnerable to erosion when rain comes. To protect soil from such a fate, gardeners apply mulch, in the form of partially degraded plant matter or plastic sheeting. Yet now, living mulches are gaining broader acceptance. Here is some living mulch surrounding a citrus tree on my balcony:

There are also positive reasons for living mulches. Plants allocate around 30% of their sugars from photosynthesis to their roots in order to form partnerships with soil microbes. Through these connections, especially connections with mycorrhizal fungi, the mysterious (and scientifically disputed) substance called humus may form. Humus has seemingly fantastical forms and capabilities- it is a kind of plasma, a colloid that holds water in the soil, as well as carbon, increasing the carrying capacity of the land over time. Thus if plants are grown to cover the surface of the soil, and if the conditions are in place to promote the flourishing of a diverse microbial community, humus will tend to grow, and the carrying capacity of the land may increase over time.

My first introduction to a kind of eco-communitarian critique of plant spacing was in the short book by Australian writer and gardener Jackie French titled Companion Planting (1), which I read while during high school. Rather than rehashing the aphorism that “basil loves tomato,” French argues in a no-nonsense style that plants are cooperative as well as competitive, and the trick is to find the best ways for them to cooperate, while also obtaining a harvest. Plants can help each other evade pests and attract predators, as well as sheltering each other from the elements. These positives make an entangled existence with other plants a sensible proposition.

I never convinced my grandfather to grow companion plants under his roses, but I was successful with his brother in law, my great uncle Aeneas Delaney, who was a priest in Bathurst, NSW. He read French’s book, and became quite evangelical about it. The marigolds he grew underneath his tomato bushes helped produce the best crop of tomatoes he had harvested in years.

French argues against pruning fruit trees, and in favour of the planting of such trees more closely than conventional orchardists recommend, such that their branches and roots intertwine. She claims that this helps to mitigate the intensity of foraging by hungry birds, while leaving them a fair proportion of the harvest. Yet agricultural machinery is generally not set up for such complexity: regenerative farmers creatively address this problem in numerous ways, but that is for another article!

The dominant modern conception of plants sees them as singular and necessarily disconnected. The magnificent specimen tree, the nursery plant in a pot of bare soil, the solitary rose bush all testify to this fact. Instructions on any seed packet will specify that gardeners should space their plantings 30 or 40 cm apart, so that individual vegetable plants will not compete with one another. The reason most commonly given is the view that close proximity creates undesirable competition between plants, for both sunlight and soil nutrients. We are also told that closeness creates unhygienic conditions in which pests and diseases can flourish. For the same reason gardeners and farmers remove weeds and carefully maintain a strict separation between grass and garden beds.

In a recent interview with fellow landscape architect Margaret Roach in the New York Times (2), Thomas Rainer describes the common practice of growing plants in separation from other plants, using barriers such as mulch as “solitary confinement.” He claims that these practices deny the social character of plants and the ways in which plant morphologies such as leaf orientations actually evolved as responses to the closeness of other plants, above and below ground.

The claim that plants compete detrimentally when growing close together does not seem to be supported with regard to plants in the wild. There, it is easy to observe large and healthy trees growing in tandem, appearing almost as if they had sprouted from the same trunk. We know from rainforest ecology that understory plants photosynthesise via a different wavelength of light to the plants that reach the canopy.

We also know that saplings deep in an understory can obtain the products of photosynthesis second hand via the fungal mycelia that connects large trees with many other plants in the forest. On the nutrient front, different plants require different nutrients and will forage for these, under the right conditions attracting the appropriate microbes to their roots via exudates (sugar products of photosynthesis) so they can make nutrients available. But the point is under the right conditions. Often in the landscapes we modern humans have constructed are depleted of soil microbial diversity, so plants growing closely together will compete in a mutually detrimental way.

In the standard modern suburban and rural landscapes, plants also lack adequate interspecies relation due to monocultures, particularly in cropping. Two farmers bucking this trend are Colin Seis who developed a method called “pasture cropping” which involves direct planting of crops into native grassland, and Simon Mattson, a sugarcane farmer in North Queensland who has planted numerous annual plants among his perennial sugarcane crops. In both cases the farmers have achieved stand- out rates of carbon sequestration- an important achievement given how low most Australian soils are in carbon. Mattson has shown that building the carbon level in soils under sugar cane can be done, settling a highly disputed question. The key is biodiversity. With each new species the soil food web becomes more complex, as it will exude particular sugars, attracting different symbiotic soil microbes.

Artist Lucas Ihlein has been collaborating with Mattson, and considers him a fellow artist. They write:

the sunflowers assemble their own sub-soil community (nematodes, bacteria, animals, fungi) which flourishes around their roots in the rhizosphere. This is a different rhizosphere community to that which accompanies the sugar cane roots. This diversity (two subsoil communities instead of one) helps prevent the buildup of pest species which are attracted to monoculture crops. Hence, pesticide use can be reduced.(3)

The presence of the sunflowers invites more than biodiverse organisms in the soil. The site has now become a regional attraction, stopping by the road side to take photographs, and even holding weddings among the flowers. Ihlein and Mattson are also initiating local cultural projects including a symphony among the sunflowers with a nearby orchestra.

Such spinoffs reflect the broadening of possibility that often accompanies the act of providing hospitality to more organisms than just the crop or the animal grown for human consumption. While the motivations for this action are rarely altruistic –they are still basically instrumental- reducing costs or producing a better quality product, at the same time, developing a responsive relation with various species can help to transform motivations towards care, a theme that is echoed in my fieldwork, which I will be presenting at the "Rediscovering Soils" workshop.

Anne O'Brien

1. Jackie French, Jackie French's guide to companion planting, 2nd Edition,

(Flemington: Aird Books, 2013)

2. Margaret Roach, “Understanding What Makes Plants Happy,” New York Times,

30 April 2017

3. Lucas Ihlein and Simon Mattson, “Sunflowers as Agricultural and Cultural Change Agents,” in The Futurelands2 Newspaper, edited by Laura Fisher and Lucas Ihlein, (Kandos School of Cultural Adaptation, Kandos, April 2017), 20

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