Hi I'm in the UK, southeast. The soil is quite good I think, though I don't have a lot of experience describing soil. It's not chalky, clay or sandy. The roots of the nettles are something else, they were there for a long time before I got the allotment. I'm going down there at the weekend so I'll take a photo then.
If nettles are present in large numbers it usually a sign that the soil is good. If you don't need the space right now I would cut them down now and cover them with something and leave it until the roots have all rotted away. I would leave a smaller patch of nettles for eating/tea and making liquid fertiliser for your other plants. They are also good habitat for beneficial insect and butterflies with some over wintering in the dead stalks.
I am lucky, I actually transplanted in only one sex of nettle plant into my garden, so all I have to deal with is the original roots of the plant and no seedlings, but most folks have both.
Nettle is such good medicine, so keep some of it--be careful when cutting it down, use good gloves, I usually use rubber gloves because of the stings. Keep a small patch if you want to use it for a chop and drop fertilizer or spring collected medicine. Never use nettles for medicine or food if it is in flower as this is extremely hard on the kidneys.
Black plastic over it for a few months should kill it--especially if you spade around it to break up the roots or they will just run out from under the plastic.
The real world is bizarre enough for me...Blue Oyster Cult
We have had good success simply digging and carefully pulling nettle roots. If it is an allotment site you could do a small patch each time you are there and work your way through it. Loosen the soil first with a garden fork.
I know that some people love nettles, but I would happily obliterate them from any area when I want to regularly do intensive work - like planting and weeding a veggie patch.
Moderator, Treatment Free Beekeepers group on Facebook.
Mow and cover what you don't want. But I certainly wouldn't get rid of all (or even most of the nettles). Nettles is a most excellent plant, it has the highest protein of all plants. To us, it would be odd to get rid of nettles so you could plant a garden. Nettles is the garden. Its also good medicine. For example, yesterday one of the women here had a tooth ache. She took fresh nettles and "whipped" them across her face. It stung a little bit at first, but then its "medicine" kicked in and the tooth ache went away. Its a good temporary solution till getting to the dentist.
Another consideration is a discussion on another forum. Someone asked about getting ready for some sort of catastrophe. Replies mostly spoke of storing food, guns, medicine and such. Something I didn't notice was any talk about "the edible landscape". If we ever have a real economic/social/biologic meltdown, folks will be hungry. Your "traditional" garden of tomatoes and cabbage may quickly get eaten by the neighbors/trespassers. But very few people will know to take/eat your Jerusalem artichokes, comfrey, elderberries, may apples, locust pods, dandelions, nettles, etc. You'll still eat. Others, less knowledgeable and prepared, will not.
Creating sustainable life, beauty & food (with lots of kids and fun)
Jim Fry wrote:Nettles is a most excellent plant, it has the highest protein of all plants.
Nettles might be a most excellent plant (I will admit to never having tried them), but they are quite a long way from being the highest protein plant. Regardless, I wouldn't want them growing in my garden either. I have a couple patches of nettles on my property, but wouldn't want to be stung by nettles constantly while tending my plants.
As Jim said, the easiest way to get rid of any plant is to cover it with something until it is dead, and then immediately plant something else in the area. I sometimes mow first, and sometimes not, but covering plants always kills them eventually. I use rubber roofing material most often because I get it free, can do large areas, and it seems that it never breaks down in the sun, but I have used many things and all work, as long as you can keep the area covered until the offending plant is dead.
"People may doubt what you say, but they will believe what you do."
Companion Planting Guide by World Permaculture Association