WILDING THE GARDEN
October 2024
Moy Fierheller | Deputy Head Gardener
October begins as autumn should. The earth clings on to wreaths of mist lingering above the fields caught in low honey-coloured sunlight, the warm smell of decaying leaves rising. Great towers of cumulus clouds gather on the horizon like armies waiting to invade. The month goes on to play hopscotch with rain and sun, so just when we think we’re back in our waterproofs for good, we’re stripping layers and panting the following day.
The garden is slowly donning its seasonal coat of colours. The golden yellow stems of Chinese fountain grass (Pennisetum alpecuriodes ‘Cassian’s Choice’) holds sprays of fluffy seedheads like rabbits’ feet, and contrasts with stands of copper-orange, rigidly upright purple moor grass (Molinia caerulea subsp. caerulea ‘Heidebraut’). Two species of delicate switch grass (Panicum virgatum ‘Northwind’ and ‘Shenandoah’) bring their own subtle tones to the party, the former’s bright green leaves transforming to a fresh yellow, while the latter’s tips turn a burnt red above thin tawny blades.
The autumn orange colouring of purple moor grass (Molinia caerulea subsp. caerulea ‘Heidebraut) in the left of the picture and the green base and red tips of switch grass in the Rewilded Garden (Panicum virgatum ’Shenandoah’)
There are still some plants providing colour and interest – the crucifixion thorn (Colletia hystrix) has only just begun to put forth a flush of pale pink, small, fragrant flowers on its spiny, leafless stems. A native to southern Chile, it is a-buzz with bees when the sun shines. ‘Hystrix’ comes from the Greek word for hedgehog, a cautionary epithet for its spiky character. In the Kitchen Garden, the blue sausage fruit tree (Decaisnea fargesii) from high altitudes in Asia, has matured enough this year to yield an impressive crop of ‘dead man’s fingers’, named for its three finger-shaped pods with a corpselike hue. When split open, they reveal hard, black, inedible seeds embedded in a sweet, gelatinous substance with hints of melon and cucumber. This jelly can be eaten straight from the pod or used to thicken preserves. We inherited some marigold seeds (possibly the Aztec marigold, Tagetes erecta ‘Calcattia Orange’) that have grown into fantastically sturdy and bushy plants, more than a metre high, just beginning to flower now with bright bursts of orange and yellow.
Left; The fragrant flowers of the Crucifixion thorn (Colletia hystrix) Right; ‘Dead man’s fingers’ – the blue sausage fruit tree (Decaisnea fargesii).
The Kitchen Garden has also been playing host to a mini digger being employed to good effect in the vegetable beds. After looking at soil samples and investigating the beds by uncovering the top 30cms, we discovered that a solid pan of compaction had been formed during the landscaping of the garden in 2020. This has caused problems not only for the crops Suzi has planted but also for the health and diversity of the soil biota. Lack of oxygen, poor drainage and restricted movement of soil organisms all contribute to a lifeless growing medium where nutrients are unavailable for plants to take up. Stuart White, who describes himself as Knepp’s heavy-duty handyman, spent two days removing the top layer of compost and breaking up the hard surface beneath to a depth of 60cms with the digger bucket. It revealed some rather foul-smelling soil and compost that had become totally devoid of oxygen, causing root death and a host of anaerobic bacteria that can produce toxins such as ammonia. Replacing the fragmented soil with a small amount of compost to keep the structure loose, Suzi and Stuart created four new beds, topped off with a deep mulch of our home-made compost. They established new paths with the addition of a bark mulch and sowed the beds with a green manure mix as a winter cover crop.
Clockwise from top left; Suzi and Stuart working to break up compaction in the vegetable beds; the foul-smelling compacted soil; the finished bed; a section of the soil profile.
The health of our own compost and the system and inputs we use is something Suzi has been continuously monitoring and updating, but we managed to take it to the next level of detail and understanding with a visit from Michael Kennard. Michael is a founder of Compost Club, a Brighton-based social enterprise. The carbon-negative company collects local food waste and creates ‘living’ compost which is then sold locally. We were joined in the Apple Store by Knepp’s Market Garden team and some food-producing friends, and Michael began with the basics: what is soil? The answer ‘geology plus life’ is seemingly simple. But it’s not readily sustained under conditions of modern intensive agriculture where artificial fertilisers and pesticides tend to destroy soil biology. He describes soil as nature’s operating system, a cycling centre processing what we might call waste (a concept that doesn’t exist in nature), where soil organisms break down organic matter producing plant-available nutrients. In a natural environment, where the nutrient, carbon and water cycles are in balance, a teaspoon of soil is so full of life it contains as many as one million species and five metres of fungal hyphae, or filaments. But the land management of the last century has led to a catastrophic degradation of living topsoil. Most intensively farmed soil is no longer living; it is a medium more accurately described as ‘dirt’ requiring applications of artificial fertiliser to enable it to grow anything. Globally, 75 billion tons of degraded topsoil – dirt – are lost through intensive farming each year, either washed out to sea with the rains or blown away as dust by the wind.
Michael thinks of himself as a microbe farmer. To him, making compost is all about cultivating soil biology and the diversity and abundance of soil species. A thriving population of microbes builds structure in the soil, reduces the incidence of pests and diseases and sequesters three times the amount of carbon found in the air. Living compost can be used as an inoculant to kickstart biology in a depleted soil. A very small amount applied as a foliar feed or added when sowing seeds or planting plugs can impact a relatively large area. Our habit of dumping huge amounts of fertiliser all at the same time can be detrimental to soil biota, overwhelming them. In nature, living organisms release a balance of nutrients over time.
What we wanted to discover was how we could do better with our own system, and two of the most important elements we learned about in more depth was oxygen supply and temperature control. Soil bacteria produce alkaline glues which bind organic matter and mineral particles such as sand and clay to form microaggregates. Fungi then chain them together to form macro aggregates, and larger organisms and worms add tunnels, all of which builds structure in the soil. Those important spaces between particles allow water and air to circulate and, like us, bacteria need oxygen to survive. In the first 20 cm of a compost heap, oxygen is readily available, but our bays get to a depth of two metres. Ingeniously, Michael replicates these air channels or voids in his Johnson -Su compost system (see below) by using what he calls chimneys. For our larger, deeper bays he recommended we plant poles down to the base at 30cm intervals while we’re building the heap and bringing it up to temperature. Moving the poles around every time material is added allows oxygen to penetrate the depths, keeping the heat produced by active bacteria evenly distributed. Unless compost is frequently turned, a bay tends to stay hot in the middle and cool towards the outside, so hopefully this method will reduce our time managing the bay. Once the bay is full, we can carefully remove the poles to leave air tunnels and shut it down to cook (we are planning to replace plastic tarpaulin with grasses cleared from the Rewilded Garden as a cap).
When adding material, we’ve begun to be much more disciplined in cutting it into smaller pieces to increase the surface area available to microorganisms and, again, increase the voids and therefore the temperature. There is a delicate balancing act between temperatures that can kill harmful pathogens and allowing the heat to build so much that it drives all the soil life to extinction. 50°C will act on pathogens and seeds in three days. A compost thermometer helps with monitoring – with ‘good’ parameters clearly marked. Thinking about farming bacteria and fungi helps us judge the carbon and nitrogen ratios we are putting in, too. Greener material feeds bacteria, more woody material feeds fungi. For hot composting, Michael recommends a C:N ratio of 30:1 but, like all good systems, having a variety of additions, including bokashi (fermenting) systems, wormery soil, and in-vessel systems like the Ridan food composter we have at Knepp, can increase diversity and abundance of life. The same goes for soil management – a diversity of disturbance, soil cover, living roots, crops and natural grazing practices enhance soil health.
We’ll keep monitoring the soil in the garden and our compost, and with a greater understanding of what healthy biota looks like under a microscope, we’ll be able to adjust our practices accordingly.
Michael Kennard explains how to add ‘chimneys’ to the food composting maturation containers; Suzi explains our bay rotation system
NASA’s Solar Dynamics Observatory recorded an X1.8 solar flare on 8 October, the X denoting the most intense type of flare. The predicted display of the northern lights, where charged particles from the sun interact with the earth’s magnetic field, was visible over Knepp by 10 October. A shimmering burst of pinks and violets it was a reminder of the power of the sun and our place in the solar system. We’re entrusted with the privilege of sharing this singular blue planet with the natural world – and it’s up to us to work out a more sustainable path of stewardship.
Photos courtesy of Karen Finley, Joshua Chalmers, Charlie Harpur.
