WILDING THE GARDEN
September 2024
In past Septembers we’ve become accustomed to the cruel irony of the sun emerging and the temperatures soaring after weeks of rain-soaked summer holidays, just as students return to school. It seems those in charge of cruel irony have decided to let the students off this year; the south of England recorded its wettest September since 1918. Cold nights in the first week saw us scurrying to move the pelargoniums and orchids from their summer outdoor spots into the greenhouse, lessening the shock to their tender leaves.
The garden still has islands of colour amongst the greens. Pale purple pom-poms cluster round the tall stems of rough blazing star (Liatris aspera) amid mauve cones of Tennessee coneflower (Echinacea tennesseensis), and the bright pops of red nasturtium and orange marigold carpet the ground beneath spires of sherbet-yellow Olympian mullein (Verbascum olympicum) above deep purple crinkled leaves of chard.
This month we began the first of a series of workshops for visitors focusing on how we manage the Walled Garden, taking what we’ve learnt from the wider rewilding project and illustrating how we implement those ideas. We discuss thinking about the garden as an ecosystem and the gardeners as ‘agents of disturbance’ driving natural processes, mimicking the free roaming herbivores in Knepp’s Southern Block; how we endeavour to create as many diverse habitats as possible, constantly grazing, browsing, rootling (in horticultural terms – selective weeding, pruning, turning soil over), so the garden is a dynamic environment offering opportunities for biodiversity to flourish.
One of the elements of this garden experiment is how we study and measure changes over time and how they relate to our actions. We have begun to keep a record of how long we spend grazing in each area of the garden, divided into 66 sections of ‘beds’ and paths, loosely monitoring where we clear, leave or drop material. Although, on the whole, it will be difficult to measure scientifically how the plant community responds to our disturbance, or lack of it, with Karen’s monthly photographic record, our time-lapse camera reels and linking hours spent with data from our soil monitoring we should be able to build up a picture over time. Our hope is that our actions will reflect an uplift in the diversity of invertebrate species – our 2023 survey showed an increase of 33% from the 2020 baseline – and we’ll continue to repeat the monitoring every three years.
We’re often asked about the high pH of the crushed concrete and sand in the Rewilded Garden, and how a build-up of organic matter might increase nutrients and, therefore, affect the plant community. Most of the plants are native to habitats with impoverished, free-draining soils such as dry stony riverbeds, prairie grasslands or mountain scree. Our hunch is that it will take a significant amount of time to see any dramatic change: the leaves of the woody plants tend to be nutrient-poor due to the cellulose and lignin they’re mainly composed of, and fungi will break down these very stable molecules slowly, although it is an important component of organic matter. We tend to leave dead stems through the winter to provide dry standing habitat for invertebrates and nesting material for birds, but we gradually clear perennial die-back through February and add it to our compost heap. Collecting data from soil samples and plant monitoring will go some way towards proving or disproving that hunch.
Our soil monitoring took a giant leap forward this month, as we were incredibly lucky to host a group of soil scientists from all over the country with a wide range of disciplines as part of a Natural England training project. Natural England advises the government on the environment, helping to protect and restore nature in the UK. Matthew Shepherd, senior specialist in soil biodiversity, headed the team. Their remit was to develop a soil monitoring programme suitable for kitchen and citizen science. Using our garden as a test site, they are aiming to build a set of monitoring tools for gardens and landscapes involved in the Weald to Waves project in which Knepp plays a major role. Weald to Waves aims to establish a 100-mile green corridor through Sussex dedicated to nature recovery. Already over 850 private gardens have registered with the project.
Matthew Shepherd taking soil samples from the Rewilded Garden, and the Natural England soil scientists Matthew, Eleanor Reed, James Hughes and Jonny Griffiths.
There were some important criteria to consider for the soil tests. The tests must suit all soil types and land uses; be relatively rapid, safe and repeatable; use freely available or cheap resources; require simple and minimal training, and record collected data, so the results are easily interpreted. While the tests are designed to assess soil ‘health’ Mathew was very keen to avoid using subjective and judgemental phrases such as ‘good’ or ‘bad’ soil – rather, to identify the ‘talents’ of a particular soil. Does it hold onto, or filter moisture? How well does it hold or lose its stability? What community of soil biota does it support? Is it suitable for food production and/or carbon storage? Does it show more resilience in the face of climate change?
After a week of trialling different methods using samples from Knepp’s wider rewilding project, a Weald to Waves corridor garden in Shoreham, and both the sand and concrete from the Rewilded Garden and the topsoil from the Kitchen Garden, we were treated to a series of demonstrations of those tests they had found to be most efficacious and straightforward.
Matthew began with simple observations, such as identifying what plants are naturally growing in the test area. The UK Centre for Ecology and Hydrology Countryside Survey has recorded all the common plants across the UK and the soils they associate with – just looking at the colour of a soil and the feel of it in your fingers can yield a great deal of information. The team also researched what resources, apps or ready-made commercial kits were most useful. They highlighted how many soil tests or charts (those relating to colour for example) are only related to agriculture, so the focus is very much on managing a soil to increase productivity and reduce stress – aggregate or sand mixes are predictably absent. Comparing commercial products of various garden centre soil-testing kits, they found them to be inconsistent in measuring nutrients and not very useful with a diversity of landscapes.
Left to right; testing for the presence of chalk; viewing soil biota using a mobile phone camera; drying soil samples for extracting soil biota.
They realised there was plenty of room for improvement, and were inventive with what resources they used – such as liquid from boiled red cabbage or red onion as PH tests; sieves, scales and kitchen roll to assess organic matter and soil stability; cress seeds to show nutrient content; cider vinegar to indicate the presence of chalk; table lamps, funnels, alcohol and mesh for extracting soil micro-organisms; and – a particular ‘wow’ moment – a jeweller’s loupe magnifier attached to a sample dish viewed through a mobile phone camera lens. Of course, this was all field work – the team will take what they’ve learned back to their laboratories and ensure that the tests are repeatable and consistent, what recording methods work best and break down how long each test might take to ensure they can engage the widest range of participants. Fingers crossed the protocol instructions for soil monitoring will be available by Christmas via a link on the Weald to Waves website as an online resource for anyone to access. The hope is that the approaches trialled at Knepp will be adopted nationally.
The last days of September – the horse chestnuts have long since curled in their burnt copper-coloured fingers and begun to drop their burnished spiky seeds. Amber warnings of rainfall and chill gusts from the north are punctuated by a few textbook autumnal days – baby blue skies, puffs of cotton-wool clouds, yellow leaves drifting in lazy spirals held in slanting honeyed light. Some trees have shrugged off their leaves early before colouring and we question if this is an indication of poor health. Ted Green, the leading authority on ancient trees who helped kickstart the Burrells’ journey to rewilding at Knepp, often says “You need to think in tree time”. Those trees that have suffered from the wet summer may just have a seasonal cold. The trees we’ve planted in the Rewilded and Kitchen Gardens are still toddlers in their lifespan. A good winter of rest and, hopefully, a warm spring next year might be all the medicine they need.
Moy Fierheller | Deputy Head Gardener | September 2024
Photos courtesy of Karen Finley, Charlie Harpur, Moy Fierheller
What we’re reading;
Modelling green and ecological corridors Show & Tell – GIGL
Top 10 garden plants for specialist bees / RHS Gardening
UKCEH Countryside Survey | UK Centre for Ecology & Hydrology
