Chemicals: using a sprayer

Sprayers are suitable for applying many garden chemicals such as fungicides, insecticides, herbicides, weedkillers, algae and mosskillers. They come in many sizes, from small 500ml hand-held misters to large 16 litre knapsacks. The large sprayers are particularly good for applying weedkillers to big areas.

Ready-to-use chemicals are very popular with gardeners and there are a wide range of products available in many sizes from all sorts of retailers. The advantages of ready-to-use products is that they are easy to use and are ready to go whenever you need them; there's no need to make up a solution. The disadvantage is the cost. It is far cheaper to make up a 3 litre (¾ gallon) solution of weedkiller from a concentrate than to buy the equivalent as a ready-to-use product. But, if you never use this much at one time, the ready-to-use option is the best one.

Remember to use separate sprayers for weedkillers, and for other purposes – if not, cross-contamination could be a problem unless scrupulous washing between materials is carried out.

Check that the sprayer is functioning correctly by filling with water and testing it, before using the sprayer to apply pesticides.

Choose a concentrate

You will need to obtain your chosen garden chemical 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/1 gallon). 

Application

• Measure out a specified volume of liquid concentrate, following the instructions on the product label, and then add the concentrate to a small amount of water already in the bottom of the sprayer
• 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

Correct angle: Keep the nozzle pointing downwards, and keep it quite close to ground level, to avoid spray drifting onto unwanted areas. The spray pattern widens with distance from the nozzle.

Spray quality and width: For most home garden sprayers this can be adjusted by twisting the terminal nozzle to select a suitable droplet size and width of overall spray pattern.

Coarse spray: This 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.

Blockages: 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.

• Although chemicals 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 spraying. 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. 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 chemical. Leaf scorch can be problematic when spraying any chemicals in the heat of the day, and the chemical 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 approximately 250ml (½ pint) of water, disposing of the washings by spraying them back onto areas suitable to treat
• Do not pour excess solution or washings down the drain - this is illegal and may pollute water supplies and ground water. 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. See our advice in chemicals: storing and disposing safely for further information

Chemicals: using safely and effectively
Chemicals: using them in gardens
Chemicals: storing and disposing safely
Chemical labels explained
Health and Safety Executive: home garden chemicals
Weedkiller damage
Weeds: non-chemical control
Withdrawn chemicals