Unless you are lucky enough to have soil that is so thin or infertile that big weeds don't grow, sooner or later you will have to intervene to keep your meadow/border balanced.
The biggest problems are caused by the following weeds:
Stinging Nettle,
Dock,
Couch Grass,
Thistle,
Ground Elder
However, depending on your site and what is already in residence, you could get plagued by virtually any unwanted plant.
So, how do we recommend you tackle this.
STEP 1 - Prevention is better than cure
It is a recipe for disaster if you simply try to plant wildflowers or bulbs (or trees and shrubs for that matter) into a site riddled with the above perennial weeds.
They will take over and crowd out your flowers.
So you must remove them, and you have two options.
The most environmentally friendly way is to dig out the roots by hand. Well, as many as is humanly possible, anyway. Nettles for example, have stringy tough yellowish roots that stretch apparently uncontrollably into the surrounding soil. However, you can kill them off with attentive weeding. It just takes time, and is easier done in stages.
The other more effective way, is to use a contact weedkiller. This can either be non-selective (usually Glyphosphate-based), or selective if you want to preserve any grasses (various types available). It is not damaging to the environment in the medium or long term as it breaks down on contact with the soil, only killing plants that are growing at the time and absorb it into their leaves and roots.
It is not dangerous to animals and does not kill pollinators and other fauna. Although it is recommended that you keep pets away from it whilst actually applying it and for a couple of hours after, just to be safe.
So how does recommending using weedkiller, fit with our environmental ethos?
Well, it is worth remembering that there are weeds everywhere, but meadows and wildflower borders are rare. It is a fact of life that you have to kill the former, to achieve the latter. On balance, it is not harmful in the short term and in the medium and long term, you will greatly enrich the environment by planting native species.
You only need to do this once - it cannot be done once a meadow is planted (see STEP 2 below) - so the environmental scales tip in favour of making wildflower habitats - in our view.
There are also many other factors to bear in mind. Meadows are low maintenance, so you use less fuel and produce less CO2 mowing. Meadows absorb and STORE, up to 3 tonnes of CO2 per acre per year, and can offset your carbon footprint by 25%. This is 100% better than a mown lawn, which produces so many cuttings it produces methane when it decays, actually detracting from your efforts to save the World! Methane is a powerful greenhouse gas.
We use Glyphosphate weedkiller without guilt, but only because we know we are making such a rich environmentally beneficial habitat in return.
STEP 2 - Dealing with big weeds, in an established meadow/border.
You basically have the same two choices.
You can dig out big Nettles and other weeds, once or twice a year. We do it at the same time as the Spring and Autumn cuts. You won't get them all, but a few don't hurt, and what you are doing is just helping nature to keep a balance of multiple varieties.
OR, you can use one of the weedkiller gel sticks/pens available in all good Garden Centres or online.
These are much less indiscriminate than applying weedkiller spray. All you have to do is grab a leaf on the growing weed, and rub on a patch of gel from the dispensing stick/pen. You don't need much per weed. The plant absorbs the weedkiller, and will die completely over the coming 4-8 weeks, depending on the time of year.
This is a very efficient way of managing a few big weeds, as it doesn't involve any digging. There is virtually no environmental impact as the weedkiller biodegrades quickly.
We recommend the following weeding routine, depending on your site conditions:
INFERTILE - Once annually at the same time as the Autumn cut, or before the weeds self-seed - whichever is sooner
STANDARD - Twice annually, at the same time as the Spring and Autumn cut.
FERTILE - As per standard, but with selective weed-killing in June or July in addition, as far as is possible, to try to get any weeds out before they seed in your meadow.