Nettles form a mass of yellowish roots, from which they happily re-grow. Now nettles tend to be full of goodness (yes you can eat young ones) both for us and the allotment. Taking frequent cuts will, eventually, kill the plant off.
If you have a patch of nettles in a corner of your plot, use them as a compost mine. Take cuts before they go to seed.
Otherwise, dig out the roots and watch out for re-growth from the small pieces you are bound to miss.
Nettles prefer an acid soil and liming to a PH above 5.5 or 6.0 seems to really slow them down. Glyphosate herbicide is medium effective – may need 4 applications to kill off an established patch.
Where there are nettles, you will find docks. They have a long tap root from which they will re-grow. You have to dig out the root and then kill it. You can either leave the root to dry out or drown them in a barrel of water to do this.
Be careful about rotovating where there are docks – the root cuttings will all leap up multiplying the problem.
Glyphosate herbicide is effective, allow time for the roots to die before cultivating.
Quoted from allotment-garden.org
Creeping buttercup is a perennial weed particularly troublesome in moister soils where it grows strongly and roots deeply.
After mild wet winters and in heavy soils rich in clay, creeping buttercup spreads widely using runners in the same way as strawberry plants will do at the end of the fruiting season. It is difficult to eradicate from amongst permanent plantings in borders and in the fruit garden.
Dig out all plants complete with root and all runners; do not compost the roots or runners as these will continue to grow and spread in your compost heap. Your bonfire heap is your friend in curing this plant.
If you have buttercups in fruit beds, you need to remove them completely using a trowel.
This weed’s presence often indicates the need for improvements to soil structure and drainage. By digging in compost, well rotted manure and other organic material over the winter you will improve the soil structure which will help to cure the conditions that creeping buttercups so enjoy. Better soil structure may well improve the drainage too.
But it may well take more than one winter to achieve the soil structure improvements. Do not expect instant results – time and patience, more compost, well rotted manure and other organic material will win through though.
Couch Grass Roots as shown on RHS website
Couch grass often grows in among cultivated plants. It’s a clump-forming perennial that spreads through the soil via underground stems or stolons, and is easily spread by cultivation. It can creep from lawns to infest flower and vegetable beds. Couch also produces flower heads that are followed by seeds, allowing the further spread of this weed.
Couch grass spreads easily to form dense mats of underground stems. It grows among cultivated plants, competing for water and nutrients and reducing crop yields in vegetable beds.
Dig out all the roots and underground stems of this grass, especially at the edge of infested lawns. Where couch is growing in permanently planted borders, it’s easier to lift all the plants and tease out the weed from the root balls. Regular slashing of the grass with a sharp knife will further weaken and loosen the plant.
Use a systemic weedkiller on couch grass in spring. Re-apply throughout the growing season at four- to six-week intervals.
Join the Prudhoe Gardeners’ Association group over on Facebook for informal questions and discussions.
You can get to know some of those who have allotments and some of those who are on the waiting lists there.
We are a friendly bunch who like questions and will answer if we can.