Weed-infested ground cover becomes an eyesore rather than an attraction, and once difficult perennial weeds are established among the plants, control is extremely difficult. A ground cover plant will win the battle with the weeds, once established. Even the best will require help initially.
Some gardeners have an aversion to chemicals in the garden, but herbicides make the job so much easier that it is worth considering their use initially even if you resort to hand weeding afterwards.
Land that is totally overgrown may need a total weedkiller, such as glyphosate, applying a few weeks before cultivation begins. It is difficult to dig ground where tall weeds are growing, and there’s the chance of chopping up the roots of pernicious weeds such as couch grass (Agropyron repens), also known as quack grass, and horsetails (Equisetum spp), which in effect propagates them. You will then have to wait until they produce enough growth again for systemic insecticides such as glyphosate to work.
The advantage of glyphosate in comparison with older total weedkillers such as sodium chlorate is the ability to plant almost immediately, though it’s best to wait for a week or two to ensure that the weedkiller has worked its way through the plant and killed the roots as well as the top growth.
Once deep-rooted perennial weeds have been killed it is comparatively easy to deal with annual weeds and the seedlings of perennials-many will germinate once the ground is cultivated, but nothing more dramatic than a hoe is necessary to control them. If you want to use chemical control for these, there are weedkillers that kill the top growth quickly and leave the soil free for almost immediate planting (in Britain, paraquat with diquat is used).
There are soil fumigants that will kill many of the dormant weed seeds as well as the growing weeds. Calcium cyanamide and metham are used in the States, but in Britain, soil fumigants like this are not used by amateurs.
If you don’t want to use weedkillers, there is no option but to dig out as many roots of perennial weeds as possible, then keep hoeing the soil as new shoots or seedlings emerge. This may have to be done over a period of weeks or months, and it is better if the soil is not repeatedly dug, as more and more weed seeds will be brought to the surface. If the weather is dry, water the area to encourage seedlings to germinate quickly.
As the absence of light will eventually kill all weeds, a mulch of black plastic sheeting is another very effective non-chemical approach. If you can leave it in position for six months or even longer, the ground will be ready for cultivation, but of course this will bring more seeds to the surface to germinate. It’s better to leave the black plastic in position, and plant through it. There’s the advantage that you don’t have to wait, provided you keep the planting holes small for the plants so that bare soil is not exposed.
The plants will in time cover the plastic, which will eventually disintegrate, but in the meantime you can improve the appearance by applying a covering of gravel or pulverized bark mulch.