‘Green-fingered folk, help me out!’ This week, DJ Sara Cox sent an appeal out on Instagram asking how to tackle newly sprung weeds. And if you have paving – whether that’s a drive, side return or patio – chances are, you can relate. It’s the time of year when weeds burst through slabs and brickwork and grow at an alarming rate.
Sara, 51, showed her followers around her paving and ‘bin area’, pointing out rogue plants, and asking for tips and advice on what to pull up and whether to leave any in situ for pollinators. ‘I don’t want to use any poison,’ she said. ‘and some of it is so pretty. Thoughts, please, on what to do.’ More than 700 people responded, with advice including to use a boiling-water-bleach-and-lemon mix, salt and boiling water, white wine vinegar or even washing-up liquid to kill unwanted weeds. Others said to simply ‘leave ones that flower for the pollinators’.
But what does GH gardening expert Dan Cooper recommend?
‘Weeds are tenacious plants, and they like nothing better than taking up residence in the gaps between paving slabs and brick pathways,’ he says. ‘Some garden escapees, such as Mexican fleabane (Erigeron karvinskianus) and mind your own business (Soleirolia soleirolii), are extremely attractive and often welcomed for their ability to soften hard edges, but others are thugs that will run and run until every gap is occupied.
‘Weeds are looking for a firm, secure foothold that allows them to grow unhindered. The narrow gaps between paving stones and block paving provide the perfect environment. Weed seeds can germinate freely in the free-draining sand or crumbly mortar between bricks and slabs and when it rains, they harness the water as it drains away. Their roots grow down, anchoring the plant in place so it can’t be toppled, accessing moisture locked beneath the paved surface. It’s a fantastic survival strategy for the plant, but frustrating for gardeners who like crisp edges and a neat appearance.
‘If weeds in your paving are not your thing, then – you guessed it – prevention is always better than cure! Keep your patios, paths and drives well maintained by periodically renewing the mortar between joints. If they’re filled with sand or other loose material, regularly brush with a stiff brush and fill any gaps with fresh, kiln-dried sand. Perfectionists may choose to apply a specialist block-paving sealer to lock the sand in place and prevent future wind-borne seeds from germinating. This should not prevent water from draining away, but it will bind the sand together so it’s less likely to wash out.
‘Weed seeds can arrive from anywhere, on the wind, in bird droppings and on the soles of your shoes. Even your postman could be an unwitting seed-spreader! Stopping weeds from arriving is futile. It’s best to deal with a weed infestation as quickly as possible, ideally, before they set seed. Some invaders have very short lifecycles, germinating, growing, flowering, seeding and dying within six weeks, so you need to be on your guard.
‘Weeds such as groundsel and grasses have fine, fibrous roots and can simply be pulled out by hand. They may take a wedge of sand or mortar with them, so that must be replaced. It’s plants such as dandelions, docks, thistles and couch grass that create the biggest headache as they produce deep or wandering root systems that can regenerate from the tiniest fragment left behind.
How to de-weed your paving
‘My advice is to rout them out using a weeding knife or crack and crevice weeder before very carefully pouring boiling water into the gap to effectively cook any roots and seeds that remain,’ says Dan. ‘You can also use a flame gun to burn off weed foliage, but you’ll still have to get the roots out somehow. Jet washing is another option, but this is only advisable if you have firm joints between your paving stones. The risk is that you’ll loosen mortar or disturb the sand, creating even more opportunities for weeds to take root. Dan recommends these tools for patios: his crack and crevice weeder; and the Speedweeder weeding tool.
‘I am not in favour of using chemicals of any sort in my garden, but of course, there are chemical treatments available for those who want to use them. Some harness naturally occurring chemicals such as acetic or pelargonic acid and are relatively harmless to animals and children when dry. However, they are indiscriminate, so if they drift or run on to neighbouring plants, they will harm them, too. Always apply chemicals on a dry, sunny, still day and use a sheet of cardboard as a shield to stop sprays carrying on to beds and borders. I do not recommend using salt to kill weeds, as that dissolves in water and can increase salinity beyond the area you’re treating.
‘While weeds in your paving can appear unsightly and, in extreme situations, may cause it to shift about or lift up, there is a case for letting selected plants grow in areas less trodden. A frothy fringe of Mexican fleabane (Erigeron karvinskianus) is a lovely feature for softening steps, and Verbena bonariensis is delightful, rising gracefully between stone slabs. Our native primrose (Primula vulgaris) will grow very happily between paving stones, lighting up the garden with its sulphur yellow flowers in spring and biting stonecrop (Sedum acre) is a pretty, ground-hugging succulent that produces starry yellow flowers in summer. Relaxing your regime a little could provide rewards for wildlife, including butterflies, hoverflies and ground-nesting bees.’
