A Simple Guide to Woodland Soil Testing

Why Bother Testing Your Woodland Soil?

Woodland gardening is an exercise in patience and cooperation. You are not starting with a blank canvas, but with an existing community of trees, shrubs, bulbs and fungi that has been quietly negotiating with the soil for decades. Before you plant a single wood anemone or hazel sapling, it pays to know what that soil is actually like. Get it wrong and you will spend years coaxing plants that were never going to thrive, while the ones suited to your ground romp away without any help at all.

Testing is quick, cheap and strangely satisfying. You need no laboratory and no specialist equipment beyond a pH kit, a jam jar and a spade. An hour or two spent now will shape every planting decision you make for the next twenty years.

Start With a Proper Sample

Soil varies enormously across even a small wood. A sunny clearing on sandy drift may sit barely twenty metres from a damp hollow full of heavy clay, and the two will support entirely different plants. Take samples from each distinct area rather than one mixed bag from the whole plot.

• Use a clean trowel or auger and remove the top layer of leaf litter first.
• Dig to about 15cm — the depth where most woodland perennials and tree roots actually feed.
• Take five or six small cores from each area, mix them together in a bucket, and test the mixture.
• Label everything. It is astonishing how quickly you forget which jar came from where.
• Test in autumn or early spring, when soil is moist but not waterlogged.

Testing pH: The Single Most Useful Number

pH tells you how acid or alkaline your soil is, on a scale where 7 is neutral. Most British woodland sits somewhere between 4.5 and 7.5, and that range makes an enormous difference to what will grow.

A simple colour-comparison kit from any garden centre, or a cheap electronic probe, is accurate enough for our purposes. Follow the instructions exactly, use distilled water if your tap water is hard, and read the result in good light.

• Below 5.0 (strongly acid): think oak, birch, rowan, bilberry, bluebell, wood sorrel, foxglove and ling heather. Lime-loving plants will sulk and yellow.
• 5.0 to 6.5 (moderately acid): the sweet spot for most woodland. Beech, sweet chestnut, holly, dog's mercury and primrose all do well.
• 6.5 to 7.5 (neutral to slightly alkaline): ash, field maple, wild cherry, ramsons, cowslip, hellebore and hardy geraniums.
• Above 7.5 (chalky): characteristic of beech hangers and chalk downland edges. Grow wayfaring tree, dogwood, spurge laurel and mezereon.

If your soil is wildly off for the plants you long for, you can nudge it with sulphur or garden lime, but do so gently and sparingly. Woodland soils are slow to change, and dramatic interventions tend to upset the fungal networks that keep your trees healthy.

Getting to Grips With Texture

Texture governs how water, air and nutrients behave, and it is easy to assess at home with a jar. Half-fill a straight-sided jar with soil, top up with water and a drop of washing-up liquid, shake hard, then leave it to settle for 24 hours. The layers tell their own story: sand sinks first, then silt, then clay on top.

• Mostly sand: free-draining, warms quickly, dries out fast, nutrients leach away. Suits birch, pine and heather.
• Mostly silt: smooth and floury when dry, fertile but easily compacted. Ideal for ash, hazel and most bulbs.
• Mostly clay: sticky, heavy, slow to warm, prone to waterlogging in winter and cracking in summer. Oak, alder and hornbeam cope well.
• A balanced loam: the gardener's dream, and rare. Almost anything will grow.

A quick field test: roll a moist ball of soil between your palms. If it forms a long ribbon without breaking, clay dominates. If it crumbles almost immediately, you are on sand.

Does It Drain, or Does It Drown?

Waterlogging kills more woodland plantings than drought ever will. Dig a hole roughly 30cm deep and 30cm wide, fill it with water, and let it drain overnight. The next day, refill it and time how long the level takes to fall.

• 2.5cm or more per hour: excellent drainage. Choose plants that enjoy sharp conditions.
• About 1cm per hour: perfectly adequate for most woodland species.
• Barely moving after several hours: poor drainage. Either plant for wet ground or improve it with organic matter and raised mounds.

If the hole stays full for days, look at where the water is coming from. A compacted pan just below the surface can be broken up with a fork, but a genuinely high water table is a feature, not a fault — plant alder, willow, marsh marigold and ferns, and enjoy it.

Matching Plants to What You Have

The real pleasure of testing comes when you stop fighting your soil and start working with it. A damp, acid corner that seemed like a problem becomes a home for royal fern, opposite-leaved golden saxifrage and a drift of bluebells. A thin, chalky bank suits hellebores and cowslips far better than it will ever suit rhododendrons.

Keep a simple notebook of your results, plot by plot, and add notes as you plant. Over a few seasons you will build a picture of your wood that no book can give you — and your planting will look settled and natural from the very first spring.