A Clean Slate

by Three Hagges Wood Meadow in Flora (Plants), Grasses, Management, Soil, Weed control, Wildflowers 0

We had an arable field with a crop of barley awaiting harvest, and an area of damp, rough grassland when we began the fine tuning in planning our Jubilee Wood.  We knew that weed control was going to be a priority, for planting the trees, and – critically – for managing the ground beneath, and on the open ground between them.  Our aim in the long term is to enhance the ground layer beneath the trees so that it will contain the perennial species – forbs – that are characteristic of natural, even ancient, woodland.  We know that in nature this can take hundreds of years to happen.  So what are the factors that prevent or delay the process?  And what are the conditions that native woodland flowers need to thrive?  And which ones are most likely to succeed? And what are the techniques that will help us to enhance the ground layer when the time comes?

We knew that our soil was more fertile than is usually recommended for sowing grasses in the rides and glades, and very fertile soils risk the proliferation of coarse and tussocky grasses.  We knew of the range of strategies that other people have used to try to reduce soil fertility, some of them expensive, some disruptive of the soil structure and profile, all of them long-term.  Which of them would be useful and practicable for us on this site? Should we even try to reduce fertility?   What are the management techniques that will achieve our aims on this site?

One of the first possibilities that we considered for soil preparation before planting – soil inversion with a Bovlund plough ‑ appeared to kill several birds with one stone.  It is a technique that promises a clean slate. It involves turning the soil to a depth of one metre, thus burying surface weed seeds at such depth that they cannot germinate. It brings the lower layers of soil – infertile subsoils ‑-to the surface, thus providing the low fertility conditions that, allegedly, fine grasses and other wildflowers need to succeed.  It loosens the soil at depth to permit deep and rapid penetration of roots, thus enhancing growth and establishment of the trees.  It is usually combined with the sowing of cornfield annuals, as a nurse crop for the meadow perennials to help suppress any weed seeds that might germinate.

Cornfield annuals, including Papaver rhoeas, Poppy, and Centaurea cyanus, cornflower. Photo: Andrew Hill, licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license

We visited a site where soil inversion had been done – and decided that it wouldn’t work for us.

The most obvious reasons being our very high water table, coupled with the field drains that empty excess water into dykes, which such deep cultivation would disrupt and thus create a swamp.  We had grave misgivings about the effects on the natural soil flora.  On the positive side, in the first year, the cornfield annuals had been beautiful, and inspirational. By the third year, tree growth was impressive, and the flora at ground level diverse.The diversity, however, included several undesirable species.  There were huge numbers of self-sown willows, coarse grasses, dandelions, thistles and ragwort, which will become dominant.

The possibility of our grassland being similarly invaded gave us food for thought, and refined the list of questions we have to answer.  It made clear the importance of a detailed management plan.  It also led us to look more carefully at the nature and competitive balance of the seed mixes we will use for our glades and rides, and consider how we might give the species in them a fighting chance against vigorous plant competitors.