How deep must the boundary wire be laid for robotic mowers?

In order for robotic mowers to know which areas of the garden they should mow, or conversely, where the boundaries are that they are not allowed to cross, it is necessary to lay a boundary wire in the ground. When laying it, one of the questions that arises is how deep the boundary wire must be laid.

Most robotic lawnmowers work with a boundary wire that is laid along the edges of the lawn. An emitted signal informs the robotic lawnmower of its permitted area. This helps prevent flower beds from accidentally being cut or the robotic lawnmower from ending up in the neighbor's garden. To help prevent damage to the wire, the question arises as to the depth of the boundary wire in the ground.

Function of the boundary wire on the robotic lawnmower

The vast majority of robotic lawnmowers work in combination with a boundary wire. This is connected to the charging station and is laid once completely around the lawn. Obstacles such as flower beds or a garden pond are also included in the guidance of the wire before the wire docks back at the charging station at the end. An electrical signal is generated, which indicates to the robotic lawnmower a boundary that must not be crossed.

Laying the boundary wire above or below ground

Basically, there are two ways to lay the boundary wire:

  • above ground
  • underground

When laying above ground, you simply fasten the cable along the route with lawn nails. Before laying it, mow the lawn as deep as possible and make sure that the boundary wire is fastened tightly to the ground. After just a few weeks, your lawn should grow in and the wire will no longer be visible.

When laying the boundary wire underground, it should lie a few centimeters deep under the turf. This has the advantage that you can scarify the lawn  and minimize worrying about damaging the cable. Conversely, if the cable is laid underground, it is more difficult to locate and repair any damage. Hence, both options have their advantages and disadvantages.

What is the right depth for the boundary wire?

Manufacturers give an indication of the maximum depth to which the boundary wire should be buried in order to avoid signal interference. As a general rule, this value is between 3 and 7 cm. You can lay the boundary wire under stone walkways or flagstones.

However, if the boundary wire is too deep in the ground, there is a risk of signal interference. On the contrary, if you lay it only one or two centimeters deep, you run the risk of the wire resurfacing the next time you scarify.

In principle, a laying depth of about 4-5 centimeters is optimal. This helps protect the cable from the scarifier, but the signal should still be reliably transmitted.

Tools for laying the boundary wire at the right depth

For creating the trench in which the boundary wire will be laid, there is a whole range of conventional and rather unconventional tools. In any case, it is helpful to first draw an auxiliary string at the distance from the edge of the lawn specified by the manufacturer and then dig a straight trench.

Marking the trench works well with an old flex. A chain saw (with the chain) is also suitable. This has the advantage that it can be used to make deep and somewhat wider slots, which in turn are also suitable for thicker boundary wires. The same applies to a hand-held circular saw. Somewhat more time-consuming but still possible is a large pizza cutter.

Alternatives are a spade or lawn edger with which the cutting of longer distances can be very time-consuming. A lawn edge trimmer with a blade and a swiveling cutting head is more practical. If you turn it 90°, you can achieve a small trench.

Finally, there are professional cable laying machines mainly used by professionals. These are guided on wheels along the edge of the lawn while a metal disc cuts the turf. The purchase of such a device can be expensive, so it may be beneficial to either rent it or hire a professional to install it in the lawn. This may help ensure that the device worksproperly and minimize troubleshooting.

In addition, there are also tools for laying the boundary wire in depths which the cable can be sunk evenly deep into the ground.

Tips for laying the perimeter wire

When buying a robotic mower, a basic set of lawn nails and a perimeter wire is often included. If the amount is not enough, the wire can easily be extended by means of a clamp but only up to a specified maximum length. The pulse emitted by the charging station is limited and, depending on the model, can only be reliably transmitted over a certain distance. If the lawn area exceeds this, interference may occur. To help prevent the robotic lawnmower from escaping, a second charging station is recommended if necessary.

Run the boundary wire around the entire lawn, starting and ending at the charging station. Also include flower beds, garden ponds or other obstacles but avoid crossing the boundary wire. Paths that are not lawn areas, but can easily be driven over by the robotic lawnmower, do not need to be marked by the boundary wire.

An alternative to the boundary wire for flower beds, ponds or obstacles are natural barriers that the robotic lawnmower simply cannot overcome. If the robot drives against a wooden or stone border, it automatically changes its direction.

When laying the boundary wire underground, it might be helpful to first lay the wire above ground and test whether the robotic lawnmower works properly. If the wire is directly laid underground, subsequent correction is not quite so optimal.