Can You Date a Hedge by Counting Its Plants? A Rule With a Complicated Record

The proposal, associated with Max Hooper and published in the 1970s, is that the number of woody species found in a thirty-yard length of hedge corresponds roughly to its age in centuries, so a hedge with five species is about five hundred years old. The reasoning behind it is that a hedge is typically planted with one or two species and accumulates others over time as seeds arrive and establish, at a rate that is slow and roughly steady. Hooper derived the relationship by counting species in hedges whose planting dates were known from documents, and the correlation in that sample was real and reasonably strong, which is why the rule became widely known and widely used.

The objections are substantial and each has been documented:

• •The relationship was derived from hedges in particular regions and does not transfer everywhere
• •Hedges planted with several species from the start begin with a high count
• •Hedges created by leaving a strip of woodland uncleared begin with everything the wood contained
• •Soil, climate and what grows nearby determine how fast species can arrive
• •Management affects survival, with heavy cutting and spraying removing species
• •The scatter around the relationship is wide enough that any individual hedge may be far off

The rule retains value when treated as one line of evidence rather than a measurement. Counting several lengths along a hedge and averaging reduces the error from a single unrepresentative stretch. Comparing hedges within one area, where soil and climate are constant, is more informative than comparing across regions. Combining the count with other evidence is what makes a conclusion defensible, and the other evidence is frequently decisive on its own, including estate maps, enclosure awards, tithe maps and aerial photographs, which date field boundaries directly where they survive. The presence of particular indicator species associated with ancient woodland, the shape of the boundary and its relationship to other features all contribute. A count alone supports a suggestion and nothing more.

Understanding why hedges exist explains what they contain. The primary purpose is a stock-proof barrier, achieved by laying, meaning partly cutting through each stem near the base and bending it over to grow along the line, which produces a dense living fence that thickens rather than gapping as a dead one would. That requires species that tolerate the treatment and regrow vigorously, which is why particular shrubs dominate planted hedges. Secondary purposes include marking a boundary in law, providing shelter for stock and crops, supplying wood for fuel and tools, and producing fruit and nuts. Each purpose favours different species, which is part of why species counts vary. The practice of laying declined with wire fencing and has been revived as a conservation skill.

The interest is not antiquarian, since the age of a boundary carries practical consequences. Ancient hedges support far more species than recent ones and are treated as a distinct habitat, with legal protection in several jurisdictions depending on age and on associated features, which means dating affects whether a hedge can lawfully be removed. Field patterns record how land was organised and reorganised, with irregular boundaries frequently indicating piecemeal clearance over centuries and straight ones indicating planned enclosure at a known date, and reading a map of boundaries reconstructs agricultural history directly. Losses have been enormous, with a very large share of hedgerows removed during twentieth century agricultural intensification, which is why what survives is documented and defended.

The rule counts woody species in a thirty-yard length and reads the number as centuries, on the reasoning that species accumulate slowly and steadily. It fails where hedges were planted with several species, were left from woodland or sit in conditions affecting colonisation. Used as one line of evidence alongside maps and enclosure records it remains useful, and alone it supports nothing.