Perennial weeds are a recurring nightmare for most gardeners and whether you garden organically or with the help of synthetic chemicals or are laidback about weeds, you can't ignore them.
You can easily cope with annual weeds, such as groundsel and shepherd's purse. Their roots are shallow, so you pull or fork them out and chuck them on the compost heap. They rot quickly, become friable compost and are returned to the ground in a year's time.
Perennials are a different kettle of fish. Long-lived plants such as dandelions and couch develop impressive root systems. Dandelions send down a tap root which breaks when you try to dig it out. Couch and ground elder quickly spread throughout an entire bed, growing through and between the root systems of plants you are keen to grow.
However laissez-faire your approach to gardening, tolerating perennial weeds would mean they throttle the flowers and shrubs you want. Disentangling the roots is a nightmare in a row of raspberries. The fruit canes throw out lots of new roots that will become next year's canes and it's quite a challenge sorting weed from raspberry. It can be much the same in an herbaceous border, where hand weeding can be almost as damaging to your favourite plants as the weeds themselves.
You could try to solve the problem by applying weed killer. I wouldn't condemn anyone for applying a few judicious strokes of glyphosate on bindweed leaves. Although this chemical is damaging to aquatic life and farmers can damage soil with repeated applications, I haven't seen any evidence that one application of glyphosate on a dock leaf kills or damages anything else.
Don't get me wrong, incidentally – I'm not urging you to buy glyphosate. On the contrary, I admire gardeners who are fully signed up to the principles of organic gardening.
Over several years, you can weaken and even kill perennial weeds, but only if you keep digging and pulling all the time. Robust weeds will sprout new growth within a week, so you need to be right in there with the hand fork, removing as much root as you can.
Organic methods can be used to clear a bed of weeds. Dig up your plants and, if they'll survive transplanting, thoroughly inspect the roots, removing every tiny weed fragment, before potting up.
Cover the ground with a permeable membrane and sink it to a depth of 60cm around the perimeter of the bed, preventing the weed roots from spreading sideways. Leave for two years, covering the ground with a mulch and containers. I have occasionally been driven to do this – it does work, even if it's a sair fecht.
Another problem with docks and couch is that you can't compost them. While annual groundsel is dead and composted within a year, nasty perennials need to be denied light for a couple of years, so you need an alternative.
After digging up the roots, thrust them in a bucket of water. Once the bucket is full, put a brick or stone on top of the roots to keep them submerged and cover with a lid.
After three or four weeks the drowned roots will begin to disintegrate. Strain off the liquid and use it as a feed by diluting it with five parts water to one part weed. The decayed roots can now be consigned to the compost bin. This way, the plants you want to grow get all the soil's available nutrients.
Some perennial weeds are a more serious headache. Eradicating horsetail is almost impossible because the roots grow so deep. Dig, dig, dig is the control. You can't compost horsetail (Equisetum arvense) but you can drown them, leaving the plants in water for a full two months. Lesser celandine (Ranunculus ficaria) roots contain bulbils which will develop into new plants. The only safe method is to send them for landfill.
The worst weed is Japanese knotweed (Fallopia japonica). This impressive plant was all the rage when it was introduced to the UK in the 19th century. There are no natural controls and even chemical ones are not wholly effective. The only hope is a biological control which is being trialled.
The ground it grows in is defined as "contaminated" and Sepa has devised strict guidelines on how the weed and its surrounding soil can be taken off site. You shouldn't put it in a waste or green waste bin. Contact your local authority instead.
