Shade can often be hard for any plant species to deal with, whether invasive or not. Forest canopies often stop all but the hardiest, shade-tolerant species from growing on the forest floor. Shade can even be used by gardeners and homeowners who want to keep away from chemicals as a way of fighting weeds. In this way, the plant's weakness can be beneficial to you as a way of controlling growth.
Plants gain most of their energy through a process known as photosynthesis. This biological process takes the light from the sun and converts the energy in that light to sugar. The sugar is then used by the plant to create energy to run the rest of its biological processes. A lack of light cuts this process off at the source.
Understanding the process of photosynthesis is helpful in fighting weeds, which can be killed without chemicals by using shade to stop the process. While some weeds, such as poison ivy, prefer partial shade, many do not. It is important to determine if your weeds are a shade-tolerant species. If they are growing in full sunlight, chances are that is their preference. Taking a sample to a local extension office could be helpful.
Still, despite the fact that some weeds may be tolerant of shade, all need some sunlight. Therefore, using an opaque plastic or even newspaper is often a good way to kill weeds in a natural way. Just because a species is shade tolerant does not mean it can completely do without any light for significant periods of time.
In most cases, the time it takes to kill weeds using shade is dependent upon the weed and the type of shade being used. If the light is totally blocked out, then it may kill the weeds in as little as a week or two. It is good to check on the status of the project every few days, preferably during a time of low light so that the weeds have less of a chance of recovery.
After the weeds have been eradicated, they need to be removed and a new species planted in its place. Planting a desired species, whether it be grass, shrubs or trees, will help continuously provide shade for the area. Thus, it will be harder for weeds to get reestablished in that area.