When it comes to stream restoration projects, there are 3 levels of weed control:
Skim off the surface vegetation, about 0.5 - 1 m diameter for each planting site, with a sharp spade or grubber. Plant soon afterwards. Weedeaters are not recommended as they encourage weed growth.
Ring barking is a technique for killing trees. This involves completely removing a strip of bark around a tree's outer circumference. It is a good technique for weeds that do not re-sprout from the base or heal the wound in their bark. It will not work on willows, ash, sycamore and hawthorn.
Mulching, a technique for suppressing weeds, is a smart idea where you will not be using herbicide. Refer to planting tips - mulching.
One of the best ways to reduce competition from weeds is to carry out effective spraying before you plant. This has the added advantage of making the digging easier by the time you come to plant, as the roots have begun to break down.
Killing grass with spray limits evapotranspiration and allows moisture to build up in the soil. The darker, moisture rich soil is in the sprayed area.
Spray healthy weeds on a dry, calm, frost free day.
For a good kill, spray when weeds are healthy and growing, typically spring and autumn. This way the weeds take up the herbicide more easily.
Spray in calm conditions: wind causes spray drift, which wastes spray and threatens any existing plants.
How many times should you spray before planting?
Pre-plant spray a herbicide such as glyphosate 2 or 3 months before planting and then spray again closer to planting time, ideally at least 2 weeks before planting.
Residual sprays stay active for a period in the plant or soil, threatening plants that are planted during this period.
On a stream margin and lower bank, where reasonable soil moisture levels are maintained throughout the year, spot spraying of herbicide is advisable. A small area of around 0.5 to 1 m in diameter is spot-sprayed with herbicide where individual seedlings will be planted. This leaves some of the original bank vegetation intact and reduces the potential for bank erosion while the native plants are getting established.
Away from the moist banks, moving onto flatter ground, are zones where the soil becomes drier in summer. Here, soil moisture has the biggest effect on plant survival and performance. In these zones, the better the weed control around each seedling, the better it will perform. This is where spot-spraying and/or blanket-spraying can be undertaken. Blanket-spraying is the spraying of a larger area than spot-spraying. Note that blanket-spraying can make an area more vulnerable to rabbit and hare browsing, as these pests hate long grass. Refer to the pest control section.
It is easy to kill existing plants with spray drift. Refer to weed control around natives for advice on spraying around natives.
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