Weeds do have special common characteristics. In the natural world when a tree falls in the forest the soil becomes open to the sunlight, as it also occurs with a fire, landslide, or devastating flood. Over great periods of time, some plants have developed by natural selection to take quick advantage of new opportunities. Most of this group are annual plants that produce vast amounts of seed that can be wind blown or carried in animal poop. Some are perennials that travel by root systems that can quickly spread to fill an area. All of them take advantage of their traits to grow and spread quickly – they are “opportunistic”.
Some human activities are similar to these natural activities – when a field is cleared and plowed for a crop, when a natural forest is removed for grassland or homes, roadsides, construction sites… These locations also provide great opportunity for opportunistic weed plants.
By rapid growth these plants steal space, sunlight, and soil moisture from the plants that humans desire to grow… and so we are at war with them.
To make matters worse many weed plants produce seeds that can survive in the soil for years. Digging up the garden may expose seeds that have been lying dormant. Or weed plants may have such short life spans that there can be several generations produced in one year...each time producing more and more seeds.
Many weeds have been spread accidentally or on purpose as a food crop. A plant that developed by natural selection in one part of the world can grow successfully any place in the world with similar growth conditions - Often displacing native plants already dominant in the location. There are many examples: Pampas Grass, English Ivy, the Wild Oats covering California Hills, and most of the common weeds.
Here are a few weeds that have been part of my life:
Johnson Grass: Native to Mediterranean Europe, this grass spreads by underground runners that grows and spreads so quickly that it blocks the growth of commercial crops. It was introduced as a food source for livestock is poisonous if too much is eaten.
Scarlet Pimpernel: Low growing, can cover large areas if not controlled. Flowers are open only when the sun shines. Native of Europe. A major pest in my back yard.
Goat Weed ( Puncture Vine): The curse of every bicycle rider! Found in southern Europe, southern Asia, throughout Africa, and Australia...and now introduced into the US. The seeds have a series of sharp spines -one of them always pointing upward - so that a bicycle ridden over the seed will be punctured. Perennial with a strong tap root, can with stand very dry summer conditions.
Wild Radish (Raphanus): Native to Asia , Annual or Biennial, Long taproot, May be wild ancestor of edible radish... Spreads rapidly by seed over large expanses - its tall thick growth crowds out other plants. Flowers when they first open are purple/red - but when they get older they become white. I sometimes find families out picking fresh green shoots to cook as greens - they are called wild turnip by some people.
Mustard (Brassica): Native to the entire Mediterranean region of Europe - Wide variety of varieties, all low growing annual plants. Some accounts say that the Bibles reference to the "Mustard tree" is a misinterpretation of the fact that a single seed can result in a large field becoming filled with Mustard in a few short years, so it is an metaphor for the power of faith.
Cheese Weed ( Malva ) - Native to Europe, Asia, and Africa... Wildly effective plant - produces many seeds each season - some varieties of Malva are used as food by humans. ( seeds have 21% protein ). The genus includes mallows and hollyhocks. Green leaves eaten in some cultures. The seeds have the shape of an old fashioned chunk of home made cheese.
Dock ( Rumix ): Also related to Sorrel. My Czech grandmother collected this herb every spring to make a spring tonic. After a long winter eating the foods available in winter - the vitamins in the first Dock of the spring would have a curative power! There are two varieties - the straight leaf dock and the curly leaf dock - they both have oxalic acid in them - curly more than straight...
Oxalis: A front yard filled with pretty yellow oxalis is so bright and cheerful in February - but so invasive. Each plant forms a little bulb that lies dormant until the next rainy season and then returns even stronger - This plant has a seed pod with a spring mechanism that can scatter the seed over extensive distances. Once established oxalis crowds everything and come back for more... This is top of my "Kill on sight" list
Bermuda Grass: Another arch villain - a few seeds of this in a lawn and the entire lawn is replaced with Bermuda Grass. it does produce a decent lawn in the summer if watered, but in the winter it turns brown and dead looking... Bermuda grass is always pushing the boundaries and attempting top grow into all surrounding flower beds, pathways, under rocks, around shrubs... "Kill on Sight"
Morning Glory: Perennial with deep tap root. You can cut it below the soil line a thousand times and it will still come back for more. Only solution is to dig the deep for the tap roots or use a weed killing chemical. Kill on sight at all costs!
Prickly lettuce (Lactura): Sometimes called Chinese Lettuce - has a milky sap - young plants are attractive - older plants become tall and produce vast numbers of winged seeds that are spread in the wind
Bristly Ox Tongue: Some poetic soul imagined that the leaves have the character of a cows tongue - Milky sap - Mediterranean
Dandelion: From the French : "Tooth of the Lion" - deep tap root that you must dig out completely or it will be back - leaves have been grown at a salad green, the flowers can be used for making wine, and which of us as a child did not blow the seed heads off into the wind.
