Weed Control: How To Control Weeds in Gardens, Vegetable Patches & Greenhouses in the UK

Weed Control In Vegetable Beds, Flower Gardens & Even In Greenhouses & Tunnels Is A Serious Problem For Gardeners & Professional Growers. This Article Explains How To Control Weeds By Preventative, Cultural, Mechanical, Biological and Chemical Means in the UK and Further Afield.

In the article we will cover all aspects of weed control including ….

• What Is A Weed?
• Organic V Chemical Weed Control
• The History of Weed Control
• The 5 Main Methods of Weed Control
  • How To Prevent Weeds Growing
  • Controlling Weeds By Cultivation Choice
  • Mechanical Weed Control Methods
  • Biological Weed Control 
  • Chemical Weed Control, Organic Chemical Control & Why Chemicals Aren’t Always Noxious Evil Substances
• The Future of Weed Control – Weed ID Apps, Robotic Weed Control and More 

 

What is a Weed?

Weeds are just plants growing in the wrong place. So a row of potatoes in the garden or farmer’s field is a vegetable. But if it were to grow in your lawn or a field of wheat it would be in the wrong place and a weed. If it grew in your lawn it is likely that you would mow the lawn and the potato would be destroyed.  It would never establish. As a way to demonstrate the issues I’ll now describe the farmer’s dilemma. It helps us understand how to garden more effectively. A farmer may well grow wheat after a crop of potatoes and find some “keeper” potatoes grow in the wheat. These will be weeds and, if left to mature, can cause problems at harvest time, due to the vegetation blocking the combine harvester, and will leave reservoir of potatoes on the ground that will be a weed in the next crop as well. The problem the farmer has with potatoes in a crop of wheat is how to weed them out. If there are only a few plants they can be pulled by hand (this is often called “hand roguing”). But if there are a lot they cannot be removed by hand and the only viable way is to use chemical control methods. Clearly organic farmers cannot use this method and will need to control the problem weeds by other means. To learn how to identify some weeds and how they can be used to identify soil problems click on the link  

Organic V Chemical Weed Control

The above example is the sort of dilemma we face in the garden when considering how to control weeds, especially weeds in established crops. As a gardener, like many other gardeners, I don’t want to use “chemicals” / herbicides on my vegetables or in my soil. For me it’s not a major issue though. I am now an amateur gardener and don’t have to crop every inch of land to make a living. So I can do things that would be difficult to do as a commercial grower. Certainly some growers and farmers grow organically, but if everyone were to do this the price of food would undoubtedly go up. The reason being that organic food, despite tasting great, doesn’t provide such heavy crops as the the non organic producers grow. That’s an unpleasant truth, but still the truth. I write it after years of commercial experience growing a range of crops. And I’m sure that I will get some negative comments for saying so! The further issue is that we have a world population that is growing fast, global warming that is taking some areas out of production and we have a public that wants to see more trees planted and land taken out of production. That creates a tension. However, as technology improves and we learn more about weeds I’m convinced there will soon be organic methods that can be used by all growers, commercial and amateur.  

The History of Weed Control

This is a section that will upset a few people as I’m going to mention chemical weed control again. It’s not that I’m for chemicals, I’m NOT! But I do think it important we understand the “how and why” of chemical weed control and the dangers they present. Go back far enough and weeds were just part of life if we grew crops. In fact, many plants we today regard as weeds were food crops in the past. For example, Fat Hen, Chenopodium album, was grown for its grain until around a 1000 years ago in many parts of Europe (and much later in some areas). It’s a relative of quinoa, so perhaps not so bad. But it’s low yielding and, when it appears as a weed, it decreases yields of crops such as wheat and other cereals on farms. And in gardens it will swamp out most seed crops eg carrots, beetroot, and even brassicas. Today it grows as a weed of waste land, gateways and similar. It is easily destroyed by chemical weedkillers and no longer a weed of arable crops. As mankind settled from nomadic life and developed agriculture there was a move towards more productive species and the destruction of competing weeds. In some cases this backfired and weeds that had a similar need to the crop flourished. So weeds such as wild oats and black grass flourished in corn crops. And in the vegetable garden and horticultural nursery the same happened. For example the cultivation of tomatoes encourages deadly nightshade as the life cycles and needs are similar. Of course deadly nightshade is easy to weed out of a tomato crop, but if we don’t do that they can soon proliferate. And if I were to grow outdoor tomatoes in the same ground year after year I’d undoubtedly see nightshade become a problem weed unless I undertook some sort of weed control.  

Weed Control: The Chemical Era

Herbicides are products that inhibit or kill plants. This can be either selective or non selective. The word has become synonymous with noxious chemicals but it needn’t be so. I often see people recommend vinegar as a way to kill weeds. In that case it is being used as a herbicide. Yet its a product we put on our chips, so not that noxious! In the early days the sort of product used to control weeds included industrial byproducts, sea salt, acids and various oils. The first organic herbicide, Sinox, was developed in 1896 in France. Note it was organic. Since then many more herbicides have been developed. Most are based on the oil industry and includes artificial plant hormones that can be applied pre-planting to the soil, at planting time or just afterwards or to the crop at a later stage. Some are selective and some not, some are persistent and some not. All are synthetic. Before the advent of chemical weedkillers all crops were organic and the term was never used. Since the proliferation of chemical weedkillers the organic movement has taken off with organisations such as the Henry Doubleday Research Association (HDRA) being set up in 1954. Since then it has been renamed Garden Organic and has approx 20,000 members. I used to live very close to their HQ and was a frequent visitor to their gardens at Ryton.  

“Chemical” Weedkillers!

Chemical is a very emotive word. The connotation is of evil noxious compounds that poison the world. But you and I are made of chemicals. The rain and soil that our plants depend on are chemicals. So I think we need to think carefully before we use the word chemical to mean evil. It is far better if we are more concise and talk us specific words and phrases such as hormone weedkillers and chemicals by name, eg glyphosate (not Roundup as that’s just a trade name and other products also use glyphosate). When we talk about chemicals we need to differentiate between natural chemicals such as seas salt and synthetic chemicals such as DDT! And let’s not forget that natural products such as sea salt are toxic.  It doesn’t take much sea water or sea salt to render soil too saline to grow fruit and vegetables.  

The 5 Main Methods of Weed Control

Preventative Weed Control

If we can prevent weeds spreading seeds, germinating and growing we will have a garden where the plants we choose will have no competition for moisture, light, nutrients etc. But it’s not something most of us enjoy in our gardens as weeds are a major problem for most gardeners and commercial growers. However, it needn’t be like that. No Dig has been a revelation for many gardeners as it means we are growing in fresh, almost weed free compost. The few weed seeds that blow in are easily controlled simply by pulling them out by hand. There are so few that it is a simple task. And if we plant good size module raised plants, that grow away fast, they soon swamp out the few weeds we might miss. In the traditional garden high planting densities also help, but we start with a situation where last years seeds are in the ground and wanting to grow. So we need to prevent them germinating. Digging and rotovating will bring seeds to the surface from the soil’s “seed bank” and the weeds now have a start. Research shows that many plants need light to grow. But not much to stimulate them into growth. A split second of light as the soil is turned is enough to stimulate them. And they are now primed to grow.   It’s like lighting the blue touch paper. If these primed seeds are within a few millimetres of the surface they will undoubtedly germinate once the moisture and warmth levels they need are present. In a sense this is good, we can use this to advantage as I’ll show under the cultivation techniques section.

Herbicides

From a herbicide point of view the use of pre-emergent products is now a consideration. They will prevent the seed germinating or damage it in the early stages. There aren’t many that can be legally used in vegetable gardens. But paths and lawns are another matter. Pathclear is frequently used by gardeners to keep paths and drives clear of weeds. And in garden lawn, products containing 2,4-D plus mecoprop-P or 2,4-D plus dicamba are typically recommended. Personally I prefer a wildflower meadow! The organic alternative for paths and drives include the use of a flame gun.  It’s much greener, though is oil or gas based so not perfect. Weed suppressing fabrics are another possible method in some areas. But again the fabrics are often oil based. Because I don’t like using synthetic hormone based weedkillers I much prefer No Dig. Based around cardboard and compost it is much greener and breaks the weed growth cycle. In a sense it is a form of mulching. But it’s not the only one that can be used. I use grass cuttings on my beds to smother weeds. If they can’t grow they can’t seed and therefore the cycle is broken again. It’s much preferable to synthetic chemical products.  

How To Prevent Weeds Growing

As indicated above weeds are encouraged by the right conditions. So if we can cut out the light they need to photosynthesise, the moisture they need to grow, etc. we can prevent them growing. The use of mulching fabrics / weed suppressant fabrics certainly cuts out light and kills many weeds. Used wisely they help a lot. In my freshly plant shrub beds I’ll lay cardboard around the plants to smother the weeds in the early stages. To make it more attractive I might cover the cardboard with bark, compost, gravel or whatever suits the area. I try to avoid fabrics however.

Strawberry beds

My strawberry beds start with layer of weed suppressing membrane, either cardboard or fabric. I cut slots in it to plant the strawberries through and weeds are banished. Without weeds competition for light, nutrients and water they grow very well. The method also prevents mud splashing onto the fruit and makes picking easy. Another light exclusion method is to lay membrane between plant rows. To me its a bit fiddly, but it works.  What is easier is to lay strips of inverted guttering between rows. It both excludes light and directs any rain to the rows where the veg is growing. Inverted guttering is a great hiding place for slugs. So you can dispose of them when found.   Another way to prevent weeds growing is to drench them in hot water. It scalds them and kills them instantly …or at least it kills the top growth, roots might survive if well established.

Dont worry about boiling a kettle to get hot water. Just leave a hosepipe lying in the sun.  The water in their soon gets very hot and used judiciously on pathways and drives will keep them weed free.  And all at no costs! What’s not to like?  

Controlling Weeds By Cultivation 

Cultivation methods to control weeds are an important consideration. By cultivation I mean things like hoeing. A long handled hoe and a short handled (onion) hoe are essential in tradition gardens.  Used properly, when conditions are right, they will control most weeds. The right time is when weeds are small and the weather is warm and dry. A wind also helps. What you are trying to do is cut the weed in half. The wind and sun will dry out the top part and it’ll soon disappear and without leaves the roots soon die. The exception are those weeds with strong root systems such as couch grass, dandelions, nettles and brambles. Persistent and or perennial weeds often need the roots to be destroyed by digging them out. otherwise they just sprout more shoots and continue growing. Stale seed beds are another control method. The idea here is to prepare the soil a week or so in advance. Let the weeds germinate and then kill them without hoeing. An ideal method is with a flame gun. Though you could use a sheet to exclude light and starve them out that way. Then you sow or plant your crop into the stale seedbed with as little disturbance as possible. The technique depends on the majority of weeds in the top few centimetres germinating and being killed. Subsequently, as the crop grows you may need to hoe any weeds that have since germinated. But there will be far fewer.

Starve the weeds as a form of control

On farms where we’ve started to see couch grass in a field we would starve it to death! For example if it was in corn after harvest we would plough and cultivate the field. This broke the couch roots into pieces (we are often told this is a bad idea .. it isn’t). then as it started to grow we would cultivate again and break it up some more. Some would be deposited on the surface each time we cultivated and the sun and wind would dry it out.  The remainder was repeatedly cultivated every few days. New shoots were broken off and the feed reserves in the root depleted over time. Eventually, with constantly being hammered like this, the roots died. Starved or energy and nutrients. The method same works for nettles, docks, bindweed, brambles etc. But it takes time and energy! On small areas I might do this and use a sheet to cut out light between cultivation. Without light the weed succumb even quicker. The beauty of the above method is that it’s completely organic. For small quantities of soil, for example the quantities you might want to use in pots, try heat sterilisation. Sieve the soil to remove stones and other large debris and put the moist soil in microwave or oven to heat it up. The steam produced kills the weeds, pest and diseases. This is how the Victorians treated their green house soil. Except they pumped steam into the soil via pipes in the ground. In the 1980s I also use this method to steam sterilise my greenhouses. We didn’t know about oil and global warming then! In fact the government advice at the time was to increase CO2 levels in greenhouses by burning paraffin heaters in them, as it increased yields.

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More to follow in a few days

Mechanical Weed Control Methods

Biological Weed Control 

Chemical Weed Control, Organic Chemical Control & Why Chemicals Aren’t Always Noxious Evil Substances

The Future of Weed Control – Weed ID Apps, Robotic Weed Control and More