Advice
RHS Help & Advice
Using a sprayer to apply weedkillers
Images: RHS
Sprayers are available in most garden centres and DIY chains, and make the task of applying weedkiller to a large area much easier.
Remember to use separate sprayers for weedkillers, foliar feeds, and pesticides - if not, cross-contamination could be a problem. Weedkiller damage is one of the commonest problems dealt with by the RHS Advisory Service.
You will need to obtain your chosen weedkiller as a concentrate for dilution inside the sprayer. Concentrates come in liquid or solid form, solids being either powders, crystals or granules. Liquid concentrates usually have a measuring cup in the lid, but solids may need to be weighed out with an old set of household scales set aside for this purpose. Some solids come in convenient sachet packs, one sachet being the correct amount for dilution in a specified volume of water (usually 4-litres/0.5 gallons).
Measure out a specified volume of liquid concentrate, following the instructions on the product label (left), and then add the concentrate to a small amount of water in the bottom of the sprayer (right).
The sprayer should then be shaken or swirled gently to disperse the liquid concentrate (or dissolve a similar solid product).
Next, fill up the sprayer to the correct volume of water, as per the instructions on the label.
Screw on the lid and shake or, better still, swirl the contents to mix them.
Finally, pressurise the sprayer by releasing the central pump-action mechanism in the handle, and pump it up and down until the pressure valve hisses.
You are now ready to start spraying, using the small lever on the handle to start or stop the flow of spray. Keep the nozzle pointing downwards, and keep it quite close to ground level, to avoid spray drifting onto unwanted areas.
The spray quality can be adjusted to select a suitable droplet size and width of overall spray pattern.
This photograph shows a coarse, cone-shaped circle of spray, covering a considerable area. Coarse spray is less likely to drift onto nearby plants, and while a wide spray pattern allows quick coverage of a large area, a narrow spray pattern allows safer spraying in small areas. Remember to keep the nozzle near to the ground if you wish to spray accurately, as the spray pattern widens with distance from the nozzle.
Twist the terminal nozzle to adjust the spray quality and width. Using a coarse spray for a few seconds can dislodge accumulated residues that may be blocking the nozzle. Blockages usually become evident by a coarsening or dribbling of spray.
The screw on the handle allows ‘bleeding’ of the system above the terminal nozzle. This may be useful for shifting residues that may be blocking the lance or valve above the terminal nozzle.
Tips for effective use of sprayers
- Although weedkillers sold to amateur gardeners are safe to use without any protective clothing, the RHS recommends wearing protective gloves and footwear, especially when handling concentrates, and to avoid getting the spray on your skin or clothing.
- Be aware that breezy conditions cause spray to drift, contaminating areas not intended for weedkilling. Adjusting the nozzle to produce a coarse spray will reduce the risk of drift. Avoid spraying in very windy or gusty weather.
- Keep the nozzle close to the ground, and make sure it is pointing down, not up, to avoid spray drift and the risk of facial or body contact.
- A dry day is best, as rain can wash away the spray before it is effective, or dilute it excessively within the plant tissues when rainfall occurs within a day of application. Avoiding rainy days also avoids the risk of run-off onto precious plants, compost heaps, or lawn areas.
- Avoid very hot, sunny days, as plants are less active and therefore less efficient at absorbing the weedkiller. Leaf scorch can be a problematic when spraying any chemicals in the heat of the day, and the weedkiller solution may evaporate, giving off fumes that are potentially harmful to other plants. Dry, overcast days are ideal for spraying.
- To clean the sprayer, fill it three times with approx. 250ml (0.5 pint) of water, disposing of the washings by spraying them back onto suitable weedy areas.
- Do not pour excess solution or washings down the drain - this is illegal and may pollute water supplies and ground water. Instead, try to prepare only as much solution as you need, and use up any excess, plus the rinses, by spraying onto other areas of your land in need of treatment.
Using weedkillers safely and effectively
Maya Albert