Organic weed management

Weedy Brassicas

Weeds compete with crops for nutrients, light and water. This is why it is important to keep them in check. Growing organically allows you to manage weeds creatively and effectively, by careful planning of your planting and using mulches. Not all weeds are bad - some attract pollinators and some can improve the soil. And of course, most weeds can be composted, which in turn will add nutrients to your soil.

Don't use toxic weed killers. They are bad for the environment and bad for you (see Glyphosate the Debate). First we deal with why you shouldn't use them, and then we help you manage weeds the organic way. Also, below is also a list of individual weeds - how they grow, and how you can best deal with them. Yes, even bindweed!

5 things about glyphosate

  1. It is a toxic herbicide used to kill weeds.
  2. On its own, glyphosate has limited toxicity. However, it is commonly mixed in chemical formulations to have maximum effect. These formulations, such as Roundup or Weedol Path Clear, are potentially far more dangerous.
  3. The European Food Safety Authority (EFSA) says that glyphosate is safe. However, most of their research is industry led, and they haven’t tested the various individual commercial formulations.
  4. Independent research indicates that glyphosate is not only probably carcinogenic, but that it also affects the body’s endocrine system – causing problems in the liver and kidneys. Industry testers dispute this, but have declined to reveal all the results of their safety tests.
  5. Over 30% of the bread in the UK contains traces of glyphosate. While not necessarily toxic in small amounts, this gradual and persistent intake could create a health risk.

How do I get rid of weeds without toxic chemicals (Roundup, Weedol Path Clear, Resolva etc)?

Patios/paths and other hard surfaces.

  • Use boiling water, or a sharp knife or trowel.
  • Flame or thermal weeders are effective, especially on young weeds, and relatively cheap to buy.
  • Organic weedkiller is usually based on pelargonic acid - which kills the foliage, but doesn't penetrate the root. See The Organic Gardening Catalogue
  • Vinegar is not recommended. Some local councils use DEFRA approved acetic acid (the basis of vinegar). As this acid is a chemical compound it is not organic. Domestic vinegar from a bottle has not been proved effective. Bleach is also not recommended.
  • When creating a new path or patio, make an impenetrable foundation layer: a geotextile membrane or a substantial mix of hardcore rubble and sand, firmly flattened to exclude all light and reduce moisture.
  • Cracks between pavers should be filled with mortar - not sand, which provides the ideal medium for weeds to germinate. Lime mortars are more environmentally friendly than cement mixes.*

Larger areas, such as an overgrown allotment or veg patch

  • To clear an overgrown growing area, slash down the high standing weeds and then cover with a thick compost manure mulch (at least 20 cms) and/or a plastic sheet. Without light the weeds will weaken and eventually die off. Use the slashed foliage and stems on the compost heap.
  • Dig up deep rooted weeds, such as dandelions and docks. Put foliage on the compost heap, and drown the roots in a bucket of water for a month or so. The water can be used as a liquid feed.
  • Persistent weeds such as bindweed and ground elder have to be dug over regularly, removing as much root as possible. Every little bit. In some cases, it is worth digging up individual plants which you want to keep, cleaning their roots of the weed’s root fragments, and then replacing in the bed which has also been dug over. Persistent digging, removing roots, will eventually – perhaps over a couple of years – weaken the plant and make it easier to keep on top of. Put foliage and roots (but not flowers or seed heads) into a black plastic sack. Tie up the top and leave in an out-of-the-way corner until it turns into gooey sludge, then compost it. See Individual Weed Management (below)

Remember, it is not just your own health that will benefit from not using toxic chemicals – you will be helping other life forms to thrive in your growing area. Leaving some weeds, such as a discreet area of stinging nettles, will provide food for pollinating insects, as well as leaves to make a liquid feed, high in nitrates.

Individual weed information

This gives detailed information about the occurrence, biology, persistence & spread, and organic agricultural management of more than 100 individual weeds, from dandelion to creeping buttercup, bindweed and ground elder.

The information in the section below results from an impressive and comprehensive research study conducted by Garden Organic with the help of organic farmers. Although it is addressed primarily to the agricultural audience, we thought its findings are also of interest to gardeners and allotment holders.

Weed management practices

How the organic farmer can manage weeds is explored below. Often more than one approach is necessary in practice. First, under Cultural controls, we look at how growing practices, such as crop rotation and tillage, can control weeds. Then the section on Direct contol methods examines mulching or mechanical removal of weeds. Finally Crop weeding strategies describes different crops and how farmers can manage the weeds within them.

Cultural controls

Organic farmers recognise that every element of growing is inter-linked, and that good rotational design produces healthy soil, healthy plants and good yields. Crop rotation is the cornerstone of organic farming practice. Rotation and forward planning are also important for managing weeds. In this section we provide information on growing methods aimed at preventing weed problems arising in the first place: such as crop rotation, crop management, tillage, and hygiene.

The underlying principle to prevent weeds is to produce a constantly changing environment to which no single species can adapt and become dominant and unmanageable, or return seeds to the soil seed bank.

Direct control methods

Although organic crop rotations can mitigate weed infestation, it is likely that some form of direct action will be needed against weeds to prevent crop loss. However, before taking any action – such as manual or mechanical control and mulching - it is important to assess whether the weeds present are likely to develop to such an extent that they will cause an immediate loss of crop or will store up potential future problems (e.g. by shedding seed). Some weed presence can be beneficial, for instance as pollinators or soil improvers.

Crop weeding strategies for farmers

In this section we focus on organic weed management for growers of specific crops, from alliums to rhubarb, based on the results of research work and practical experience of organic farmers.

Further information

The following papers provide overviews of weed management options for organic farmers:

A review of non-chemical weed management. Referenced review by W Bond, RJ Turner, AC Grundy, 2003
A review of the management of selected perennial weeds. Referenced review by W. Bond, 2008
Organic Weed Management - a Practical Guide, (2003) Study by Charles Merfield, Revised 2002

This information comes from a Defra-funded project conducted by Garden Organic in partnership with The Initiative for Organic Research, Elm Farm Research Centre, Horticultural Research International, ADAS and RULIVSYS in 2004 and updated in 2007.