Living Walls™ require well-draining soil. Healthy roots need both moisture and air. When soil stays saturated, the spaces that normally hold air fill with water, reducing the oxygen available to the roots and increasing the risk of root damage.
Check drainage before digging your hedge trench. Drainage can vary across even a short distance, so test at several points along the intended hedge line, particularly in low areas, heavy clay soil, areas with a high water table, or anywhere water tends to pool after rain.
Before carrying out a drainage test, look at how water behaves around the proposed hedge site. Signs that drainage may need attention include:
Recently developed sites deserve particular attention, as construction traffic can compact soil and drainage conditions can vary considerably over a relatively short distance.
These signs are useful, but a drainage test will give you a better indication of how quickly water moves through the soil.
Drainage can vary significantly along the intended hedge line, so test at several points rather than relying on a single test hole. Include the lowest points and anywhere water tends to pool.
If the hole drains completely in less than an hour, note approximately how long it takes.
Less than 25 mm per hour — Poor drainage
Address the cause before installation and, where appropriate, use a raised installation.
25–75 mm per hour — Generally well-drained
Usually suitable for standard in-ground installation.
75–100 mm per hour — Free-draining
Usually suitable for standard in-ground installation. Pay closer attention to watering.
More than 100 mm per hour — Very free-draining
Follow the LIGHT SANDY SOIL installation detail in the In-ground installation guide and ensure reliable irrigation.
If the results vary along the hedge line: Do not average them. Treat each section according to its drainage. If one area drains poorly, address that area before installation and use the appropriate raised installation detail for those conditions. Significant differences over a short distance may indicate low spots, compacted ground, clay pockets or changes in ground level that need separate attention.
If drainage is poor, address the cause before installing the hedge. A trench on its own will not correct a wider drainage problem.
First consider where the excess water is coming from and where it can go.
Do not add gravel, scoria, sand, compost, manure or similar materials to the hedge trench in an attempt to improve drainage.
Changing the soil only within the trench does not correct a drainage problem in the surrounding ground and can interfere with the way water moves through the soil. Sand added to poorly drained clay can in fact make drainage worse.
Living Walls™ installed in the ground should generally be backfilled with the excavated site soil rather than replacing it with a different material.
If water flows towards the hedge from higher ground, roofs, paving, driveways or other hard surfaces, redirect it away from the hedge area where practical.
Reshaping the surrounding ground may be enough to prevent surface water collecting along the hedge line.
Take care not to redirect water in a way that creates a drainage problem elsewhere.
Compacted soil restricts both drainage and root growth and is common on building sites.
Where the soil is compacted, dig the trench wider than the minimum dimensions if practical. Break up hard or compacted soil at the sides and base of the trench with a spade, and loosen the surrounding soil where practical, so roots and water can move into it more easily.
Avoid working or driving over very wet soil, as this can make compaction worse.
If there is a deep layer of very hard soil or a large area of heavily compacted ground, machinery or professional site preparation may be required.
Where water repeatedly collects and cannot drain naturally, properly designed subsoil drainage may be required.
A drain needs somewhere for the water to go. It must have sufficient fall and discharge to a suitable outlet rather than simply collecting water beneath or beside the hedge.
Where the drainage problem is significant, there is no obvious outlet, or substantial earthworks are required, have the site assessed by a landscape or drainage professional before installing the hedge.
Raising the root zone can help where the surrounding soil is heavy or wet.
For heavy clay soil, wet sites or high water tables, use the WET HEAVY SOIL detail in our In-ground installation guide.
The trench is dug about one-third shallower than the standard depth so approximately one-third of the rootball sits above the surrounding ground level. Cover the exposed sides of the rootball with soil, sloping it down to the surrounding ground.
This keeps more of the rootball above the wetter surrounding soil.
A raised installation does not correct persistent waterlogging if excess water still has nowhere to go.
Where the existing ground is unsuitable for standard in-ground installation, the hedge can instead be raised entirely above the existing ground level. This can be done by creating a raised soil berm or, where appropriate, by installing an open-bottom planter box. This may be useful where:
The raised area must provide enough suitable soil for the hedge roots and allow excess water to drain away.
Because raised soil can dry out more quickly, reliable irrigation is particularly important.
If using an open-bottom planter box, make sure it provides adequate soil depth and width for the hedge roots and allows water to drain freely into or away from the ground below. Follow our Container and planter box installation guide.
A high water table is different from surface water or slow-draining soil.
If groundwater regularly rises into the hedge root zone, surface grading or a simple drainage trench may not solve the problem. A raised or fully raised installation may be more appropriate.
Where the water table remains close to ground level or the extent of the problem is uncertain, seek site-specific advice before installing the hedge.
