Well, summer is officially over, and it is time to tidy up the allotment. It has been a good year for weeds. The rain has often kept us indoors and the weeds have taken their chance. That's what a weed is: a plant growing where you do not want it. It is biologically no different from the plants that we grow in our gardens. There is no special biological category for weeds.
Many weeds are edible and were eaten as part of the ancient diet right up to the modern period. Some foragers stil eat them. Some are plants that were once in favour and have been abandoned. Take ground elder. This was introduced by the Romans and for many years was a staple part of the British vegetable diet. It has a taste of parsley, but has now been abandoned and is simply seen as an invasive weed of gardens. Fat hen and good King Henry [to be distinguished, please, from bad Henry, a very poisonous woodland plant, also known as dog's mercury] were both eaten as part of the stone age diet. They are often found growing in hedges throughout the British Isles. Jack by the Hedge is known as garlic mustard and was once widely eaten. Young netttles are full of mineral salts and if added to a stew or soup quickly lose their sting in the cooking and are extremely edible. You will not need to add salt to a soup or stew in which you have added nettles. A good book on edible plants will tell you what you can and cannot eat, and it is a good idea to obtain one and familiarise yourself before you go foraging. It is important even for experienced foragers to take care and be sure on identification before they pick.
Yet weeds are useful in other ways. Take an example. I picked my onions, which were large and plentiful, then went off for a week in Grasmere. When I returned the weeds had taken over the onion patch. What should I do? Pull every one? Not at all. I am not using that bed over winter, so I am going to leave them. They will make good ground cover before I put the plot to bed for winter by putting tarpaulins over it. As ground cover they protect the soil from damage by heavy rain and ensure that nutrients in the soil are retained in the plants' cells rather than washed away. I can compost the weeds and this way retain the nutrients.The roots of the weeds penetrate the soil during the winter period and help to maintain its structure, as they create passages fore air to circulate. Nettles have deep roots which delve down into the soil to bring to the surface nutrients that most other roots cannot reach. Hence composting your nettles brings minerals into the compost.
Gail Harland, writing in the Weeder's Digest, speaks of beneficial weeds, which are broad leaved plants that do not compete with crops. She cites studies that show that Brussels sprouts growing among weedds had fewer aphids than thsoe growing in bare soil [p30.] Some weeds, such as crow garlic, if grown near carrots confuse the carrot root fly with their powerful scent. This protects the carrots. Some weeds provide cover for ground beetles that can prey on insects harmful to the crop.
There is a happy medium to be struck. Eliminating every weed is impossible, and trying to do so loses some useful plants; on the other hand you cannot let them grow wild. Some weeds, for example Japanese knotweed, Himalayan balsam and giant hogweed have to be eliminated, and nettles make a painful presence on any plot. Bindweed strangles other plants. All of these have to be eliminated. On the other hand ground elder makes a perfectly pleasant contribution to your salad, as do dandelion leaves. Just make sure that you don't pick the wrong types of weeds. As I said, a good guidebook is very useful, indeed essential if you are inexperienced.