Thistle: how to avoid being invaded and eradicate it?


There are many species of thistles (Carduus). These plants of the family Asteraceae are, for many of them, considered to be harmful plants with very high power of dissemination having a considerable impact on the balance of ecosystems. This is the case of Canada thistle (Cirsium arvense). Moreover, the law requires its destruction according to article L251-3 of the Rural Code. Here is how to proceed for a successful deflection.

Knowing how to recognize Canada thistle

Also called Cirse des champsThis very common thistle in Europe is actually classified as an extremely invasive weed. It grows rapidly in wastelands, ditches, meadows, cultivated fields and of course in gardens because it has a great capacity to adapt to various environments.

The wind spreads its seeds up to 150 meters around, and a single thistle can produce up to 40,000 of which about 300 eventually germinate and what should be noted is that they are able to preserve their germination power up to twenty years. This thistle with branching stems, which can reach 1.50 meters in height, is recognizable by its pretty lilac-colored tubular flowers which exude a pleasant scent. Its rhizomatous roots sink into the soil up to 2 meters deep to draw essential nutrients and water.

In our country, the Canada thistle is declared pest because it is responsible for a loss of yield for the farmers. This is why many prefectural decrees force a merciless fight against this Cirse des champs.

Eradicate thistle: beware of prohibited herbicides

As much to expect, if one lets oneself be invaded by the Thistle, it will be very difficult to eradicate it completely because, as we specified previously, its seeds can germinate several years after having been dispersed by the wind. One may be tempted to use a synthetic herbicide to get rid of this weed, except that since 1er January 2019 (date of entry into force of Labbé Law or Law 2014-110) amateur gardeners (and not only) no longer have the right to use (or even own) chemical pesticides.

To eradicate Canada thistle, we have no choice but to use products authorized in organic farming provided they are stamped Authorized use in the Garden (EAJ) or even some biocontrol products or even those said low risk. It is therefore essential to be well informed when purchasing a treatment against thistles, especially since the use of a prohibited herbicide (which would have been kept in the back of a cupboard) is an offense. criminal. The offender is exposed to severe penalties, namely 150,000 € fine and 6 months imprisonment. We do not joke about the good health of the environment.

Avoiding being invaded by Thistles: prevention methods

We can prevent the establishment of Canada Thistle by using the following solutions.

  • Ask a geotextile where one wishes for example to create massifs.
  • Cover the areas where thistles grow with sheets of cardboard or some plastic sheeting. Deprived of light, the Cirses will find it difficult to develop.
  • Install a mulch at the base of cultivated plants to leave thistle little chance to grow.
  • Sow alfalfa on the plot so that the plants compete. Clover is able to deprive thistles of water and nutrients.
  • Let the thistle fly and various species of weevils which devour the Thistles.

It is best not to leave a patch of bare soil in the garden as this unwanted plant is very likely to settle there quickly.

Mechanical control of thistle: the alternative to chemical herbicides

Fortunately, there is still a solution to not let yourself be invaded by thistles without resorting to dangerous weedkillers. This is the mechanical struggle which combines various tasks, namely:

  • Manual removal of all thistles from the garden,
  • The repeated mowing and mowing of the meadow,
  • Burning,
  • Burying stubble or stubble cultivation, which is rather reserved for agriculture, for example after the harvest.

Cirse des champs being a plant particularly tough, the gardener who is invaded by it must arm himself with patience not to see a single Thistle in his garden. This is why it is strongly recommended not to allow this weed time to settle.

Here is how to proceed to eradicate Canada thistle.

  • Cut the thistle stems level with the ground using pruning shears after having taken care to put on gardening gloves. Ideally, this pruning is done as soon as possible so that the plant does not gain vigor. If you have a lot of thistles (wasteland, meadow that has not been mowed for a long time or neglected garden), it is essential to pass the mower.
  • Repeat pruning or mowing as soon as the Thistles grow back to weaken plants since their roots will gradually lack nutrients.
  • Dig the earth in order to get out as much as possible roots.
  • Burn all thistles cut as well as the roots dug up so as not to risk a new proliferation. This waste should therefore not be inserted into the compost.

It is of course possible to overcome this plant by spraying it regularly with horticultural vinegar (inedible) which overcomes this weed in a few hours. But this solution is only valid if you don’t have a lot of thistles in your garden. As to epsom salt to be distributed all around the feet of Cirse, it should be used sparingly because it prevents many plants from growing and does not only kill weeds. So be careful …

It is very important to intervene either before flowering, is while that the flowers are in full bloom. But if we wait for them to dry, the seeds will form and sow the garden as well as all the surrounding land … Likewise, care must be taken to remove all the root because the smallest piece left in the ground is enough for the Canada Thistle to regrow. By leading a bitter mechanical struggle, it takes two to three years to permanently eradicate the Thistle.