There are three main types of weedkiller: contact, which only kills the plant tissue it touches; systemic, which is taken in by the plant and spreads throughout it, killing all parts; and residual, used on paths and paving. Residual formulations may have some contact action, or may be sold in mixtures with contact ingredients, for instant effect. Be aware that some soil-acting weedkillers (such as sodium chlorate) can travel in the soil and may harm tree roots or move sideways into beds and borders. If in doubt only use weedkillers that work by contact.
The ways in which a weedkiller can be used are set out on the product label or accompanying literature. Not only are these the most effective way of using the material, but adhering to these instructions is a legal requirement. If you read the instructions before purchase, you can also be sure you do not buy more than you need; many weedkillers have a short shelf-life and are best not kept from year to year.
There will also be safety details on the label. While the weedkillers sold to gardeners are benign to the environment, pets and children, when used as directed, it is important to use weedkillers responsibly. Rubber boots, old clothes or overalls and gloves, although not usually strictly necessary, are a sensible precaution. Be particularly careful to thoroughly rinse out old containers before discarding in the refuse.
Although watering cans may be used, sprayers apply weedkillers more economically and accurately. Ideally, have a dedicated sprayer for weedkillers and another for other materials. They should be checked for leaks and blockages using clean water before use. Where a measured amount of material is to be applied to a given area the output of the sprayer should be checked first using water alone.
There is an extremely low risk to gardeners from diluted weedkiller, and the slight hazard of garden weedkillers comes mainly from the concentrate. For very small scale jobs consider ready-to-use packs. However, the nozzle design on these is inadequate for good results if you need to treat a large area.
Apply the spray using a spray sufficiently coarse not to drift but fine enough to cover the weeds' foliage evenly. Apply the weedkiller up to the given dosage per unit area or sufficient to wet foliage without run-off. Never apply weedkillers on a windy day.
After spraying, rinse the sprayer with three washes of a small amount of water, spraying this out onto weeds listed on the label. The sprayer will then be safe to store.
Exclude pets and children from treated areas until the spray has dried.
Applying spot weedkillers and stump killers
Applying weedkillers with a sprayer
Guy Barter