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Controlling weeds in the garden

Published on February 15th 2021
A close up of a flower
Weeds have been with us since mankind first started cultivating gardens. The term weed can be hard to define because a plant that is regarded as a weed in some parts of the world can at the same time be cultivated in another, like Common Purselane.
When talking about weeds, we’re referring to the wide variety of annuals as well as perennials that lavishly grow in gardens and aggressively compete with other garden plants for moisture, nutrients, and space. A weed is normally an exotic plant and most weeds arrived in South Africa many years ago and were accidentally introduced.
Weeds need to be eradicated before becoming permanently established, however, this can require considerable effort and even cost. For this reason, it is very useful to be able to identify common weeds and learn how you can control them in your garden.
White clover
In this article, we dish the dirt on some of the common weeds found in the garden, the dispersal of weeds, and how to control and discourage weeds.

Top ten troublesome weeds

  • Common sowthistle (Sonchus oleraceus)

Common Sowthistle

Sonchus oleraceus

  • Common blackjack (Bidens pilosa)
  • Khaki weed (Tagetes minuta)
  • Common ‘dubbeltjie’ (Tribulus terrestris)
  • Onionweed (Nothoscordum inodorum)
  • Winter grass (Poa annua)
  • Bur clover (Medicago polymorpha)
  • Yellow nutgrass (Cyperus esculentus)
  • Common couch grass (Cynodon dactylon)
  • Khaki bur weed (Alternanthera pungens)
A close up of a flower
Dandelion | Taraxum sp.

What stimulates weeds to germinate?

There are three key ingredients to the germination of weeds. Knowing what these are will help you control weed germination and growth in your garden.
  1. Disturbed soil - Weeds thrive off disturbances, mechanical or fire, most as we know are fast-growing pioneers. Some weeds opportunistic annuals and fast-growing perennials and other are transformers - plants introduced without their predatory hosts.
  2. Sunlight
  3. Moisture
White clover

Weed seed dispersal

Weeds are mobile in the seed stage and dispersal can be due to human activity, either deliberate or opportunistic (fodder, stick to clothing etc.).
Weeds are incredibly effective dispersers, whether via seed or vegetatively. Some use wind for dispersal (Dandelions), some hitch a ride (Opuntia species), and others produce thorns that stick to feet or other passing objects (Tribulus sp. or Alternanthera pungens).
Weeds can spread via active vegetative dispersal like the spines of Opuntia species that attaches to clothing or to the fur of animals. Weeds can also spread passively like the Mother of millions (Kalanchoe delagoense) that drops its leaves with vegetative buds to the ground to eventually form a new plantlet.
A close up of a green plant
Mother of thousands. Photo by @majapapaja.

How to discourage and control weeds:

Make use of mulch (organic and inorganic)
Mulch discourages weeds and promotes ground living organisms and protect the soil.
When preparing the garden, especially the vegetable garden, for planting, it’s good to leave the ground for two weeks to allow annual weeds to germinate, giving you an opportunity to remove before sowing desired crops or flowers.
Learn more about mulching in the article below.
Make use of groundcovers
Pioneer plants or weeds thrive with soil disturbances and lots of sunlight. By planting groundcovers that serve as a blanket over the soil, prevents weeds from finding a patch of fertile soil to settle into.
Here are a few examples of effective groundcovers:
A plant in a garden
Mechanical weeding (best when small)
Cut non-stoloniferous weeds with secateurs at soil level, to create as little soil disturbancemas possible. The roots will become compost.
Cover soil with a black plastic
Another method for preventing weeds from germinating is covering the soil with black plastic to prevent light from infiltrating to the sil, inhibiting the germination of weeds. Instead of using chemicals to kill weeds, plastic is a less toxic alternative.
Do not let weeds go to seed
Nip weeds in the bud before hundreds of seeds germinate in the next season. When discarding seeds also ensure that you get rid of all the plant material as these might be carrying seeds.
A close up of a plant
Soil steaming sterilization
Soil steaming is a way of sterilizing soil with heat. This is usually a nursery practice. Weeds along with plant pests are destroyed in the process.
Chemical means
Selective herbicides can be applied to weeds, such SnapShot to inhibit weed growth. Chemical spraying, however, is not good for the environement and can have a detrimental effect on pollinators, beneficial soil bacteria and fungi, and other advantageous organisms.
A man in a garden

Alternative uses for weeds

When it comes to weeds, it’s not all bad. Some weeds have numerous benefits and uses including edibility, medicinal, ornamental and binding carbon. Below are a few examples of useful weeds.
Edible and medicinal
Weeds you can eat. No need to dispel all weeds to the compost heap. A simple meal can be tasty as well as remarkably nutritious and healthy by piling them up on your plate. Most weeds can be used the same way as spinach and other leafy veggies.
Other edible weeds include:
  • Young leaves of Sowthistle (Sonchus oleraceus) are edible.
  • Leaves of Dandelions can be enjoyed as salad and roots roasted as coffee substitute.
  • The subterranean nuts of Cyperus esculentus are edible.
  • The leaves of various Amaranthus species are edible and other enjoyed as a salad or spinach. A. deflexus, A. thunbergii, A. hibridus and A. spinosus.
  • The young leaves of Vicia sativa, Broadleaved common vetch, are edible.
  • Young leaves of White Goosefoot are edible.
  • The sprouts of Blue Dandelion are edible as well as the roots of the coffee.
  • Leaves of Stinging Nettle are edible.
  • The ripe, mature, black berries of Nightshade are edible.
Environmental benefits
Some weeds have proven to provide good sources of pollen and nactar for bees and other pollinators. Dig into the Knowledge collection below to see which weeds are beneficial to pollinators.
A close up of a flower

Other common weeds

Learn more about weeds in the KNOWLEDGE section or dig into the collection below.

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