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Weeds and Weed Control

The use of chemical weedkillers is a highly emotive subject, with many people being strongly against their use.  We at MyGardenSchool prefer not to use chemicals where possible, but regrettably accept that their use can occasionally be deemed necessary.  Having said this we believe that in a domestic situation 99/100, a manual solution will do the job as well, if not better than using a chemical spray.  Do you have an opinion on this?  Do you think there are any occasions when it's acceptable to use chemicals?  We'd love to hear your thoughts  - please post in the comments section.

So what is a weed? The short answer to that question is: any plant growing where It Is not wanted. For instance, a grape seedling germinating in your dahlia bed is a weed - unless you want a vine amongst the dahlias. In a stricter sense, weeds are the native ancestors of our cultivated garden plants; they are undesirable because they are less attractive, generally bear smaller flowers or fruits, and are more vigorous in competition with their descendants. Weeds compete for water, nutrients and light, and often deprive cultivated plants, especially the seedlings and young ones, of their fair share of these necessities, because weeds adapt better to less favourable conditions.

There are two basic types of weeds - perennial and annual: the former are far harder to eliminate


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Most perennial weeds are quick-growing and tenacious, often re-growing from roots or rootstocks. They are, therefore, very difficult to get rid of. Herbaceous types, such as couch grass, bindweed (Convolvulus and Calystegia species) and ground elder are often notoriously deep- rooted. They store food in their fleshy roots, rhizomes, stolons, tubers or bulbs. It is easy to remove the visible vegetation but difficult to eradicate the roots. With woody plants, such as brambles and ivy, it is harder to get rid of the growth above ground, but comparatively easy to erad­icate the roots, which must be burnt.

Manual weeding

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We would always recommend hand-weeding as one of the best and safest ways to rid yourself of perennial weeds. Some well-timed work with a trowel will save you much time and trouble later on - providing you don’t leave any of the roots in the soil.

If working near decorative or vegetable plants where you don’t want to use chemical weedkillers, then manual weed­ing becomes a necessity. You may need to use a fork, trowel, knife or even a mattock (like a pickaxe). Be careful that you don’t just carve them up; this merely helps to propagate them and makes more work in the future. Dig up the weeds, complete with roots, and then burn them or put them in the garbage bin.

When cultivating fresh ground it is essential to remove all the roots and underground storage systems; although hard work, it pays to lift them out by hand. Don’t use a rotary cultivator on couch grass or dock-infested land as it will only chop up the weeds and encourage regrowth. Hoeing can have the same effect j on a smaller scale unless you take care to remove the root, not just chop off leaves.

If you have large areas of ground to cover and are not restricted by time, then covering the ground with thick black plastic sheeting or an old carpet to smother the weeds and deprive them of light will eventual kill even the most stubborn of perennial weeds, provided you keep out all sunlight for a minimum of 12 weeks.

Cut down all weeds with a strimmer or scythe and cultivate the soil either by digging over by hand or by using a rotary cultivator. remove as much root and leaf as possible and then cover the ground so no sunlight can penetrate through.

Any weeds which are still present will germinate again, but will quickly use up the stores of food in their roots and will die off due to lack of light.


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As we have said before weedkillers very hugely from country to country but may are now banned in Europe and the States, but may still be available in some parts of the world.  You will need to seek specific advice from your local nursery or hardware store as to what is available to buy locally and always follow the manufacturers instructions to the letter.

Weedkillers are categorized according to their mode of action, so that you can buy whichever is most suited to your needs.  In an area devoid of decorative or culinary plants you can use a ‘total’ weedkiller,  to ‘sweep the board’. A total weedkiller will kill all plants with which it comes into contact. You must take great care not to let it drift onto other plants or onto your neighbour’s property. There have been many skirmishes over the garden wall as a result of misapplied weedkillers.

Residual weedkillers are best for clearing paths and driveways.(Commonly bought as combinations of chemicals weedkillers such as glyphosate/oxadiazon/
diflufenican or *glyphosate/flufenacet/metosulam depending on manufacturer)

Residual or pre-emergent These will not kill established weeds but they help to prevent the germination of most weeds for up to three months. There are various degrees of persistence.

This type remains in a narrow band of the topsoil, so that any weed seeds germinating in this zone take up the chemical and die. It is possible to apply residual weedkiller where bulbs are planted, because their roots are located below the weedkiller band, and they grow quickly through it without suffering any damage. Plants such as runner beans, sweet peas, daffodils and hyacinths will all grow through the weedkiller layer after it has become inactive.

Some weedkillers are termed ‘selective’ as they kill dicotyledons (broad-leaved plants with two embryonic/seed leaves or cotyledons), but will not damage many monocotyledons - such as grasses. Selective ones like 2,4-d, mcpa,

Two of the best know non-selective weedkillers are paraquat and diquat weedkillers These will only kill perennial weeds while they are still at seedling stage. After a few weeks they become immune and these preparations merely burn off their foliage and allow the roots to re-grow. They are de-activated immediately they meet the soil and are therefore safe to use provided they do not drift.

In the United States, paraquat is available primarily as a solution in various strengths. It is classified as "restricted use," which means that it can be used by licensed applicators only. In the European Union, paraquat has been forbidden since 2007.

Methods of application

Always read the maker’s instructions on the package and follow them closely; they have been based on years of research. Our recommendations give the chemical name, so when buying proprietary brands check the package label and see that it contains the correct constituents for your purpose. Keep a separate watering can for use with chemical weedkillers, and use a rose fitting or dribble-bar attachment for controlled application.

Specific treatments

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Couch grass and perennial oat-grass These persistent grasses, with rhizomes, put up a fight against eradication. The only effective control is dalapon.(banned in Europe) or isoxaben.  If they are found in flower or vegetable beds 'spot' apply several doses and then dig out the remains.

‘Spot treatment’ involves applying the weedkiller to the weeds only. It is done most easily by using a bottle with a pourer top or a squeezy-type container.

Perennial nettle, bindweed, ground elder and blackberry These tend to grow near hedges or in shrubberies, and once established are likely to remain per­manent residents. Apply brushwood killer (usually Triclopyr) but avoid spraying onto other plants.

A good way to minimize drift is to make up a solution of this weedkiller in a container and dip the tips of the weeds in it. This will then be taken up through the plant by the sap stream - and kill it. You may need to make several applications over a few days for them to be effective. This method also works on many wild, shrubby plants such as dog rose and ivy (Hedera helix).

Thistles These are particularly obstinate weeds that may need pulling out by hand.

Lawn weeds

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The rosette-forming types (such as daisy, dandelion and plantain) are the most successful on lawns as they tend to escape the lawn-mower blades. To spot-apply weedkillers to lawn weeds use a small dropper bottle.

Dandelion, daisy, creeping buttercup, rib­wort and plantain Proprietary lawn weed­killers containing mcpa and 2,4-d with mecoprop usually bring quick death, but must be applied in strict accordance with the makers’ instructions. .

Use repeated doses of mecoprop. Feeding the lawn with sulphate of ammonia should hasten the expiry date.

Two very difficult grasses to remove from lawns are couch grass and perennial oat-grass.  Close and frequent mowing will go a long way towards finishing them off; otherwise you must dig them out with a knife. Effective weedkillers cannot be used as they would kill the lawn as well.


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Annual weeds, by definition, mature, flower, seed and die within one year. ‘Seed’ is the operative word here, because this is the method by which they repro­duce and infest the garden. It is also the key to their control;

if you can remove the seed before it reaches the soil you can stop the next generation of weeds before it starts.

Many species of annual weeds grow quickly and succeed in completing several generations each year. The seeds seem to be able to germinate at any time of the year, even the middle of winter. So never assume that weeds are ‘out of season’; although they may grow more slowly in winter they are always lurking.

Some of the most common annual weeds that you are likely to encounter are; chickweed, speedwell, groundsel, knot­grass, shepherd’s purse, annual nettle, charlock, sow-thistle, scarlet pimpernel, goose-grass and wild radish.

Weeding by hoeing

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One of the most common, and time- honoured, ways of controlling annual weeds is by hoeing. The secret of suc­cessful hoeing is to choose a day that is dry, sunny and, preferably, has a steady breeze. All these factors help to dry out the weed seedlings on the soil surface and prevent them re-rooting.

Don’t just decapitate the weeds when you hoe; make sure the roots are removed.

In a way, you make extra work for yourself by hoeing because you con­stantly bring more weed seeds to the surface where they germinate. Seeds can remain viable in the ground for years, waiting until they come near to the surface before starting to grow. Some seeds are very sensitive to the amount of daylight available and can only spring into life when they are in the topmost layer of soil. Regular hoeing, however, will keep weed seedlings under control.

Controlling with weedkillers

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Most annual weeds are more easily controlled by weedkillers than their perennial counterparts. A whole range of annuals succumb to applications of glyphosate.  Diquat is also very useful for killing germinating weed seedlings. You can spot apply it anywhere provided you take care not to let it drift onto other plants.

Unlike many perennials, annual weeds germinate within the narrow soil-surface band to which the weedkillers have been applied; therefore they die almost as soon as they start growing. So, on the whole, these weedkillers tend to be more effective against annuals. Always remember where these chemicals have been put down and make sure that no horticultural activities ‘break the band’ as this will allow the weeds to come through unscathed.

Annual lawn weeds

As well as the tough perennial lawn weeds, you are also likely to encounter some troublesome annual ones. One good preventive measure is to use a grass- collecting box on the lawn-mower. This will stop many weeds falling back on the lawn and propagating themselves. Chickweed Best controlled with meco­prop which is often applied with 2,4-d as a general lawn weedkiller.

If you would like to learn more about all aspects of gardening, landscape and garden design, why not consider taking one of our 4 week Online Gardening Courses where you will be taught by some of the world’s leading experts and get 1-2-1 feedback and personal supervision.

Now we have told you our thoughts, why not share your own views?  Tell us how you control weeds.  Do you Use Chemical Weedkillers? …. If not why not?

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