Weedkillers are often the most effective solution for controlling weeds, and may be the only way of dealing with some persistent perennials.

Weedkiller Action

Weedkillers work in one of the three following ways:

1. Contact Action

The chemical kills off all parts of the plant that it comes into contact with. Weeds must be sprayed thoroughly to be effective. This technique is useful for destroying annual weeds; however, as the roots are not destroyed, perennials will usually re-grow.

2. Systemic Action

The chemical is sprayed onto the leaves and then taken inside the weed and moved around its system so that the whole plant (including its roots) is affected. The effectiveness is increased if the weed is in vigorous growth. As the root system is also poisoned, this technique is useful for both annual and perennial weeds.

3. Weed Preventers

Weed preventers can be applied to the soil, where they are absorbed by the roots of plants. As they remain active in the ground for many months, they will also kill any new weeds as they germinate, preventing them from establishing. They are an effective way of killing and suppressing annual and perennial weeds. Do bear in mind however, that as they remain in the soil for some time, you should wait until the manufacturer's recommended period has elapsed before sowing any plants or crops.

Application Types

There are three major types of weedkiller application available:

1. Foliage activated: Applied by spray, and enters the plant through its leaves or stem. Works by contact or systemic action.
2. Soil activated: Applied to the soil, and enters the plant through its roots (used as a weed preventer).
3. Selective: Most kill broadleaved plants, but leave narrow-leaved grasses unharmed; however, there are some available that do the reverse, and leave ornamental plants whilst killing grassy weeds. Works by contact or systemic action.