Horsetail, mare’s tail

Horsetail, or mare’s tail, is a prehistoric, pernicious, spreading, perennial weed that can quickly colonise and take over large areas of the garden.

It spreads through its black, creeping, perennial “roots” – actually underground stems or rhizomes. These grow quickly in the soil and can spread over great distances

Horsetail creates large clumps of upright stems that can smother and kill smaller plants below and surround larger plants, spoiling their appearance. The roots can grow in between those of cultivated plants, making them difficult to remove and control.

• Beds
• Borders
• Lawns
• Gravel paths
• Between paving slabs
• Waste or uncultivated ground

Horsetail is readily recognisable thanks to its upright, bright green, almost fir-tree-like stems that appear through the soil in spring/early summer. These can grow up to 60cm (2ft) high. These are preceded in spring by shorter light brown stems with a cone-like, spore producing structure at the end – adding to its resemblance to a conifer.

It usually dies down to its roots in late autumn and winter, lulling you into believing it has gone away! But it will grow back with a vengeance the following year.

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

Remove any shoots that appear above ground as soon as they appear. This is unlikely to completely control it (unless it is a very small infestation), but can reduce it if done regularly over several years.

Digging it out can be very difficult, since the roots can go down a long way – 2.4-3m (8-10ft) and even more. But it’s always worth starting by digging out as much of the roots as possible. Be rigorous as even small pieces left in the ground can re-grow into a new plant. A fork and hand fork are usually better tools than a spade and trowel, which will cut the roots into smaller pieces.

Once you have removed most of the horsetail, covering the soil with weed-control membrane (landscape fabric) or even thick black polythene will exclude light and may starve the roots, so they die. This can take many years until the horsetail is 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 tease out all the horsetail roots. Then replant in clean soil or pot them up for planting out later.

In lawns, regular mowing throughout the year, and possibly together with the use of lawn weedkillers, should certainly weaken it and may eventually kill it.

For a novel method of control, cut and harvest the stems regularly. Ancient Greeks and Romans used to use it as pan scouring pads, thanks to its high silica content! A positive use from such a negative weed.

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

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. Unfortunately, the leaves of horsetail are very thin and both these and the stems contain silicon, making absorption difficult. But don’t follow the advice of damaging the stems before applying the weedkiller.

To ensure the weedkiller works effectively:

• Spray the plants when they’re growing actively; this is mainly from May to September/October.
• 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 when the growth first emerges through the soil – wait until the stems are around 30-45cm (12-18in) high.
• 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 horsetail. You will need to spray once, allow the horsetail to die down, and then spray the regrowth again. Three or more applications a year, over a couple of years, may be needed to completely kill it, depending on how extensive the root system 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.

Roundup Gel, which is smeared onto, and sticks to, the weed, may be a better option than a liquid spray. Where possible, place a sheet of rigid plastic, or similar, behind the stems to hold them in place. Then smear the gel along the whole length of the stem.

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

As horsetail spreads by its underground 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 horsetail in their garden.

However, as the roots can go down several feet, putting a vertical physical barrier in the soil on your boundary is unlikely to prevent it coming in.

• Spade
• Fork
• Hand fork
• Weed-control membrane
• Systemic weedkillers
• Lawn weedkillers