Creeping thistle

Creeping thistle is one of many different types of thistles, which is characterised by its creeping lateral roots that grow horizontally. It is a perennial weed that can spread over verge large areas, making it very difficult to control and eradicate, especially if allowed to become established.

These lateral roots are very brittle and readily snap or break off when cultivating the soil or trying to dig up the plants. Even small pieces of these roots will reshoot to produce a new plant.

As the roots spread for some distance, creeping thistle quickly produces large clumps. And, as the leaves are very spiny, these become a real nuisance.

The flowers also produce huge numbers of seeds, which are carried long distances by wind, spreading this weed even further.

• Beds
• Borders
• Lawns
• Gravel paths
• Waste or uncultivated ground

Creeping thistle has typical thistle-like spiny leaves. It produces flower stems up to 90cm (3ft) high, but heights can range anything from 30cm (1ft) up to this height.

These flower stems produce typical pinky-purple thistle flowers from July to September, giving rise to thousands of feathery seeds that are carried over long distances by winds.

As with most perennial weeds, never allow creeping thistle to become established. This will make it more difficult to fully control. Early identification and eradication is very important.

Start by digging out as much of the creeping thistle as possible, including the creeping roots. The roots are brittle and break off, and can go down some distance, making them difficult to completely dig out. If you intend to use digging the main method of control, then you will need to be persistent over several years once it becomes established.

Regularly hoeing the new leaves as soon as you see them will weaken the plant over time, but this will probably take several years to completely kill plants – and needs lots of dedication to not allow them to grow.

Covering the soil with weed-control membrane (landscape fabric) or even thick black polythene will exclude light and may starve the plants, so they die. This can take several years until the plants are completely exhausted and eradicated.

If the roots are growing among established plants, you may have to lift these when dormant, from autumn to the end of winter, and carefully tease out all the creeping thistles. Then replant in clean soil or pot them up for planting out later.

In lawns, regular mowing throughout the year and the use of lawn fertilisers and lawn weedkillers may weaken it and eventually kill it.

You may unknowingly introduce creeping thistle into your garden when buying topsoil or manure. So be vigilant when buying these.

There are a number of weed control options available to treat creeping thistle. In addition to traditional weedkillers there are now also a range of more natural alternatives.

Contact weedkillers will burn and kill the foliage, but will have no effect on the roots, which will continue to grow, produce new leafy growth and spread further.

For best results, spray with a systemic weedkiller. A systemic weedkiller, which is absorbed by the leaves, then moves down to the roots to kill them.

To ensure the weedkiller works effectively:

• Spray the leaves when the creeping thistles are growing actively; this is mainly from March/April to September/October. Plants are at their weakest just before flowering.
• The larger the leaf area present, the greater the amount of weedkiller that can be absorbed and move down to the roots. So don’t bother spraying until the leaves have enlarged.
• Use a fine spray to thoroughly coat the leaves in small droplets.
• During the summer, spray in the evening to prevent the spray evaporating and to give maximum time for the spray to be absorbed. In spring or if overnight dew is forecast, spray earlier in the day to allow the spray to dry before dew falls.
• One application of weedkiller is unlikely to kill all the creeping thistles. You may need to spray once, allow the plants to die down, and then spray any regrowth again. Three or more applications a year, over a couple of years, may be needed to completely kill it, depending on how extensive it is.

Most contact weedkillers are total weedkillers – that is they will damage or kill any plants whose leaves they are sprayed on. Make sure you keep the spray off wanted plants – including lawns – and, if necessary protect plants by covering with polythene or similar when spraying.

Use weedkillers safely. Always read the label and product information before use.

Never allow plants to flower and set seed. Although this is pretty easy in your garden, it’s more difficult to stop the seeds blowing in from a neighbour’s garden, any surrounding fields and waste ground and even further afield.

As creeping thistle spreads by its lateral roots, it may be coming into your garden from a neighbouring garden or surrounding waste ground. Unless you can stop this source, it will just keep coming back.

If it’s coming from a neighbour, have a quiet word and try and encourage them to control the creeping thistles in their garden.

If it is coming through from a relatively small area, it is possible to put a vertical physical barrier in the soil on your boundary to prevent it coming in. Suitable root control barriers and membranes are available from builders’ merchants.

• Spade
• Fork
• Hand fork
• Hand trowel
• Weed-control membrane
• Weedkillers
• Lawn weedkillers