Countering weeds effectively is a major challenge in municipalities and agriculture. Chemical products are available, but they are often harmful to the environment and can only be used in a limited way in public spaces. Hot water can be used to remove dandelions, thistles, etc. without the use of herbicides – a much gentler process for the environment and for surfaces.
Unlike cultivated and ornamental plants, weeds are plants that grow naturally without human intervention. There are many good reasons to control weeds: In agriculture, to protect crops. In towns and cities, to keep public spaces clean and tidy and to prevent damage to roads, open spaces and buildings.
Many weeds can spread extremely quickly and/or cause severe damage with their roots. They also have a negative impact on the desired aesthetics.
Thermal, mechanical and chemical methods can be used to destroy weeds. These methods differ, among other things, in terms of their environmental impact, sustainability and effectiveness. An overview of treatment methods:
Hot water machines | Hot foam machines | Hot steam machines | Hot air machines | Flame devices | Weed brush | Spray method | |
|---|---|---|---|---|---|---|---|
Type of method | Thermal | Thermal | Thermal | Thermal | Thermal | Mechanical | Chemical |
Properties | Up to 98 °CKill the parts of plants above ground and the roots below using hot water. | > 100 °CSteam cleaner with additional foam production. The foam is used for insulation purposes and is intended to prevent the steam from cooling too quickly. | > 100 °CKill the parts of plants above ground. However, heat transfer from steam is nowhere near as effective as that from hot water. Roots are not effectively attacked. | > 350 °C Kill weeds using intense heat from hot air. | > 400 °C The plants are heated using burning gas, causing them to die and partially burn. | Weed brushes and strimmers remove the plants from the roots. | Herbicide is applied to the leaves using a spray unit. |
Environmental impact | Low | Moderate | Low | Moderate | High | Low | Very high |
Effect | Plants and roots are weakened and destroyed, including the seeds. | Plants are weakened and destroyed. Limited penetration. | Plants are weakened and destroyed. Limited penetration. | Surface growth is destroyed. Limited penetration. | Surface growth is burned. Limited penetration. | The parts of plants above ground are removed using a steel brush. No penetration | Herbicide weakens and destroys the cell structure of the plant down to the roots. |
Noise exposure for users | Low | Low | Moderate | Moderate | High | Moderate | Low |
Special requirements | Can be used on all surfaces, including critical and hard-to-reach areas. | Can be used on all surfaces, including critical and hard-to-reach areas. | Can be used on all surfaces, including critical and hard-to-reach areas. | Ineffective in moist conditions. | Cannot be used in extremely dry conditions, ineffective in moist conditions. | Standard in public areas; achieves desired clean, smart look in towns and cities as the weeds are removed directly. | Generally prohibited, may be used on paved and compacted areas only with special authorisation, certificate of expertise required. |
Sustainability/effectiveness | High | High | Moderate | Low | Low | Moderate | High |
Application frequency | Up to four applications in the first year, decreasing the following year. | Up to four applications in the first year, decreasing the following year. | 4–6 applications. | Application must be repeated about every 4 weeks. | Application must be repeated about every 4 weeks. | Application must be repeated about every 4 weeks. | Up to four applications in the first year. |
Overall assessment | ***** | ** | *** | ** | ** | *** | ** |
The overview of treatment methods shows: Weeds can be removed effectively using various thermal methods. The principle of thermal weed control is based on a basic biochemical rule: Most proteins denature from a temperature of around 42 °C. This means that the proteins change, break up and are no longer able to fulfil their functions.
The heat required for this can be generated and converted in different ways: As a direct flame or indirectly via thermal radiation, as hot water or steam. Hot water is the only chemical-free method that also reaches the roots. Even if the roots are not immediately completely destroyed, the weed is further weakened with each application of hot water. If it is regularly applied right from the beginning, regrowth is impeded and the application frequency will significantly decrease as early as the second year. As a rule of thumb, three to four treatments a year are sufficient.
The best time to remove weeds is in the afternoon. The amount of water stored by plants varies depending on the time of day. It is best to start with the first hot water application shortly after the weeds have sprouted in spring. This is because as plants get older, they become more resistant to hot water.
The critical factor when removing weeds with hot water is the temperature: The hotter the water, the more efficiently the plants can be eliminated. Hot water high-pressure cleaners can offer a consistent water temperature of up to 98 °C, which is just under the steam limit and is therefore ideal.
Weed removers are ideal accessories. Depending on the size of the surface and required use, these vary in terms of working width and area performance.
The optimal distance between the nozzle bar of the Kärcher weed remover and the surface is between 5 and 15 centimetres. It is possible to work comfortably within this range without the weed remover touching the ground. It also means that the loss of water temperature as the water travels to the surface is minimal.
