Winter finally arrives, the garden edged with white, glistening as the sun emerges with two hard frosts in quick succession. The colours of autumn are clinging on, and that golden slanting light picks out the last of the leaves on the trees and hedgerows laid out like an epicurean feast – hues of gingerbread, honey, carrot cake, caramel and marmalade. It’s easy to forget the singular beauty that can be found in the dark months.
Frost melting on switch grass (Panicum ‘Shenandoah’) in the Rewilded Garden
We’re wary of last year’sextremes that saw us lose too many tender plants in the cold side of the greenhouse. So, we rolled out long sheets of fleece to cover the tree echiums, pelargoniums and the large tender salvias, lending the space an air of Miss Havisham’s ghoulish chambers. We face the annual conundrum of how to stop heat escaping in the ‘hot’ side that hosts an elderly radiator and three doors. Insulating blinds and double glazing are prohibitively expensive, and we await that clever inventor who can come up with a sustainable and affordable solution. Things have moved on in the world of bubble wrap, with plant-based, biodegradable products readily available. There is one snag – its deep green tinge means we can’t be sure it will allow enough light through for germination of spring seed sowings. Instead, we’ve tried to cut down our usage of the old-school bubble wrap and sectioned off half the area encompassing the radiator, and shut down one of the doors, squeezing in the houseplants, orchids and cuttings. We wait to see how this section copes with the coming season’s unpredictability.
We’ve been looking back on the year with a degree of wonder at how much we achieved – 87 safari tours and talks, opening for the National Garden Scheme, hosting 11 work-experience volunteers, as well as running Knepp Volunteer and Plumpton College student days. All of this, through the hottest June on record, a relentlessly wet autumn and the most named storms since the system began in 2015. We’ve supplied the house with seasonal vegetables through the year, planted hundreds of annuals and some new small trees, 600 summer bulbs in March and another 200 in the autumn. Charlie H, meanwhile, designed and oversaw an entire new landscape and courtyard garden at the new Knepp Wilding Kitchen & Shop site which opened in September.
The year also saw us making a concerted drive to curb the enthusiasm of our resident field voles and their forays into our bulbs, vegetables and roots. The Narcissi are safe – all parts of the plant contain a toxin called lycorine that poison the digestive system, with the highest concentration in the bulb. It also contains microscopic, needle-like chemicals called oxalates that cause burning and irritation. It is generally only humans that mistake the bulbs for onions – voles, like all other mammals, seem to have evolved the sense to steer clear. Although the jackets of tulips – a fine, papery sheath surrounding the fleshy white bulb and the outer layer – contain the chemical tuliposide, which causes skin irritation to humans and stomach issues if ingested, voles seem to counteract this by eating them from the pointed end inwards and in small quantities. Unfortunately, a half-eaten bulb is as unproductive as one which has disappeared completely. Since voles don’t hibernate, the bulbs are a good source of fat in the lean months.
A typical neat tunnel burrowed by a vole in search of tulip bulbs planted in the Rewilded Garden
Isabella Tree, Knepp’s owner, put out a call to the Rewilding Advisory Board for their thoughts and experiences on vole control. One member suggested a novel new canapé for the Wilding Kitchen: vole-au-vents. It’s possible the work involved might not merit the reward, although there is some evidence to suggest Neolithic people ate them. Alastair Driver, director of Rewilding Britain, told us he’d had some success with liberally planting caper spurge (Euphorbia lathyris) also known as ‘mole plant’, around vegetable and flower beds. The milky sap is toxic and can deter burrowing. Since they seed freely and have been used for hundreds of years as a medicinal plant, they can definitely take a rightful place in the Kitchen Garden.
Caper spurge (Euphorbia lathyris), or mole plant, which can deter moles with its milky sap
One of the issues with a walled garden is that – intentionally – it reduces access for apex predators. We do have airborne ones living close by – kites, buzzards, owls and kestrels in the park that are particularly excellent predators of voles but, as Jonathan Spencer, former head of planning and environment at the Forestry Commission, pointed out, they all like hunting over open ground and larger areas. The dense, multi-layered vegetation in the garden (as well as human presence) limits their ability to hunt effectively. With plenty of small mammals as prey in the rewilding project around us there is little incentive for them to try their luck inside the garden. In any case, he says, predators are not the main regulatory mechanism influencing the boom-and-bust nature of vole populations. Far more important are the availability of food, outbreaks of disease and harsh weather. There also tends to be a boom cycle after major habitat disturbance, which makes sense to us since the redesigning of the garden is only just over two years old. The food element is difficult, since the Kitchen Garden is obviously all about edible plants, and we have been providing the voles with a bounty of bulbs in the rewilded pool garden. In the wild, food resources would naturally dwindle dramatically over the winter and be sought after by many competing species.
In the absence of predators such as foxes in the garden, there are other small predators that could be effective, such as adders, stoats and weasels. We thought briefly about introductions. However, stoats and weasels would eat our sand lizards, and the general public might not take kindly to a venomous snake as a feature of their garden tour.
The final recommendation, from Matthew Oates, formerly national specialist on nature for the National Trust, was to introduce a couple of semi-feral, slightly underfed, middle-aged, neutered tom cats into the walled garden. Unlike young cats or queens with kittens they are less likely to pursue sand lizards or songbirds. Yet, for us, cats seem more farmyard than rewilding – and even they would eat our wild ducklings in the spring.
The last predator on the list is, of course, ourselves. In this confined and protected space, it’s probably up to us – to some degree – to act as proxy for missing apex predators. So, to try and gauge the scale of the vole population we’re dealing with, we set snap traps in short sections of pipe (to avoid catching birds) over the course of a few weeks. As well as the steady stream of voles in the traps, (Bernard tallied 26 for the month) and the evidence elsewhere in the garden – the darting furry scurrying as we walk the paths, a lattice of neat holes in the sand and crushed concrete of the Rewilded Garden, and the large number of nests of nibbled grasses and leaves- it was easy to see that we have a significant problem.
But then there is the rewilding argument – this is a garden where we have created as many diverse habitats as possible to increase biodiversity. Essentially, we are saying “All welcome here”. As horticulturalists, we have had to retrain our mindset to see what might be considered “problems” in a formal traditional garden, such as incoming ‘weeds’ or wildflowers and plant failure, as opportunities for other life – part of the dynamic, self-willed processes we’re after. Perhaps, after all, the same could be said for voles. Our sand lizards are using old vole tunnels, and we often find toads hibernating in old vole nests. Might it be possible to simply step back and watch as these natural processes play out, wait for the “bust” years in the vole population and accept that we will just have to live without some of those tulip species that the voles find irresistible?
Moy Fierheller Deputy Head Gardener December 2023
Photos courtesy of Karen Finley, Charlie Harpur.
What we’re reading;
The Gardeners Year by Karel Čapek
Stone Age people ‘roasted rodents for food’ – archaeologists – BBC News
https://www.bbc.co.uk/programmes/m001t9pt
https://www.thehub.earth/news-1/from-springtails-to-pauropods-soil-biodiversity-monitoring-in-the-uk
