Example Garden

Your robot will deliver its best performance if your garden includes certain features.  Refer to the figure below to see examples of these important features.

Key features of the ideal garden include:

  • 150 sq. ft. maximum garden area 
  • 3” high vertical metal, wood, or brick border 
  • 12” minimum plant spacing 
  • ±1 inch maximum surface variation
  • 22 Degree maximum ground slope
  • Clear ground surface (initial weeds need to be less than ½ inch high)

Please note, the effect of plant growth on Tertill’s ability to maneuver in a vegetable garden.  The space between certain plants decreases as they grow.  At some point Tertill may become unable to reach these spaces.  After Tertill’s maneuvering space has become restricted but before a canopy has fully formed some manual weeding might be necessary in such spaces. Tertill will persistently maintain all larger, reachable spaces eliminating the need for nearly all manual weeding.


Tertill gets the energy to patrol from the sun through its solar panel.  But only a limited amount of energy is available each day. This collected energy determines how large an area Tertill can cover.  If Tertill is given too much area to patrol—more than the available solar energy allows—it cannot keep up with the weeds.  

That’s why an ideal garden for one Tertill is no more than about 150 square feet in area or say 10 feet by 15 feet.  A typical garden in the United States is about 100 square feet so one Tertill can collect enough energy to patrol most gardens.


The garden where Tertill works must be surrounded by a border of some sort.  Without this Tertill can’t identify the edge of your garden and will wander away.  The best sort of border—from Tertill’s point of view—is made of conductive material and is at least three inches tall.  Conductive materials include not only things like wire mesh fencing and wrought iron fences but many other materials that become somewhat conductive when moist.  Examples include landscaping timbers, clay bricks, stockade fences, and so on.  

Materials that make poor borders are plastic, rubber, and glass.  Decorative plastic fences and plastic or rubber edging work less well because Tertill’s primary sensor can’t detect them.  Tertill is confined by borders made of such material but it will waste energy each time it encounters such a border and will thus will spend less time weeding. 

It is also helpful to Tertill if the ground is flat near the boarder and the border wall is vertical. If this is not the case Tertill’s wheels may start to climb the border barrier before it is detected by the sensors in the robot’s shell.  When this happens the robot will occasionally get stuck, upended by the border.


Tertill can weed only those parts of your garden that it can reach.  As soon as it detects the light touch of a leaf Tertill will turn away.  This means that if the distance between the leaves of any two plants is less than Tertill’s diameter (about 8.25 inches) Tertill will not drive between those plants. Densely spaced plants can thus prevent Tertill from reaching whole sections of your garden.  

Arranging plants in a hexagonal pattern (as is shown for all crops in the drawing except the peas, beans, and onions) maximizes the space between plants and gives Tertill sufficient room to maneuver.  Tertill will have an easier time reaching all parts of your garden if at least 12 inches are left between plants and between plants and borders.


Tertill must be relatively small so it can navigate between plants and it’s wheels must be correspondingly diminutive.  The small wheels limit the largest rock or bump the robot can climb and the deepest rut it can traverse.  

Tertill is very persistent.  Regardless of difficult terrain Tertill will do its best to attack weeds in every part of the garden. However, it will do its job much more effectively with a little help.  Raking the garden so that most rocks and bumps rise no higher than one inch and ruts or holes are no deeper than one inch will allow Tertill to navigate most efficiently.


Tertill protects itself from tumbling over by turning away from slopes steeper than about 22 degrees or a 40% grade.  To make sure that Tertill easily finds its way to all parts of your garden we recommend flattening any area with a slope greater than 22 degrees.

Other Considerations

Irrigation hoses

Many gardens use soaker or sprinkler hoses for irrigation.  Depending on hose size and material Tertill may have trouble climbing over hoses lying on the ground.  Best practice is to lay the hose in a small trench just deep enough to fit the hose.  Tertill will move past such hoses easily.

Small plants

Tertill turns away from any plant taller than about two inches.  However, the garden is a complex place for a small robot. Sometimes borders, rocks, ruts, and other obstacles can cause Tertill to back up or slide sideways into a desired plant.  Small, delicate plants can sometimes be damaged in this way.  

Protecting small, delicate plants with plant collars is thus a good idea even it the plant is tall enough that Tertill usually senses it.

Low plants

Plants that hug the ground or propagate via rhizomes can present a challenge for Tertill.  The robot is only able to discriminate between desired plants and weeds by height.  Low plants like strawberries may appear to Tertill to be weeds.  It is necessary to mark such plants with plant and row collars so that Tertill doesn’t make the wrong decision.  


Plants like squash and cucumber (typically planted about three feet apart) start small but then spread out to cover a large area.  The weeding strategy for these plants must change they grow.  When the plants are small Tertill will prevent weeds from emerging within the area the plants will eventually cover.  As the plants grow the position of plant and row collars can be adjusted to keep Tertill away from their leaves.  Once the leaves are large enough that Tertill can no longer drive between the plants the robot’s job is done.  Shade provided by the large leaves will keep weeds at bay.

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