More specifically the term is often used to describe plants that grow and reproduce aggressively. Weeds may be unwanted because they are unsightly, or because they limit the growth of other plants by blocking light or using up nutrients from the soil. They also can harbor and spread plant pathogens that can infect and degrade the quality of crop or horticultural plants.
The term weed in its general sense is a subjective one, without any classification value, since a weed is not a weed when growing where it belongs or is wanted. Indeed, many "weeds" are beneficial, even in gardens or other cultivated-plant settings.
In its more specific use, weeds are naturally occurring plants, that due to their aggressive growth, are colonizers and may damage plants and landscapes that are desirable to people. Weedy plants generally share similar adaptive speciation that gives them advantages and allows them to proliferate in disturbed environments such as agricultural fields or areas with disturbed soils like roadsides, construction sites and other areas that have had the soil and/or natural vegetative cover damaged.
These plants have naturally evolved to colonize disturbed environments. These naturally occurring environments include dunes and other windswept areas with shifting soils, alluvial flood plains, river banks and deltas, areas that are often burned plus others. The weedy nature of these species tends to give them an advantage over more desirable crop species because they tend to grow quickly and reproduce quickly, have heavy seed set with seeds that persist in the seed bank for many years or short lifespans with multiple generations in the same growing season. Perennial weeds often have underground stems that spread out under the soil surface. A theory has been developed to express the interrelationship of these plants with the environment, called r/K selection theory. Invasive species are also considered weeds.
Weeds classified as noxious weeds, when left unchecked, often dominate the environment where crop plants are to be grown, often because they are foreign species mistakenly or accidentally imported into a region where they have no natural enemies.
Some weeds, such as the dandelion, are edible, and their leaves and roots may be used for food or herbal medicine. So-called "beneficial weeds" may have other beneficial effects, such as drawing away the attacks of crop-destroying insects. Indeed, dandelions are one of several types which break up hardpan in overly cultivated fields, helping crops grow deeper root systems.
Fighting weeds in your garden is an ongoing battle, but with some diligence, the amount of weeding necessary can be drastically be reduced, and with some strategic planning, you can make the time you do spend weeding much more effective.
Many weeds will sprout up after the winter rains, which is also when your garden plants need the water. Weed after these rains to ensure the right plants get the water at this time of year. Plus, you're getting the weeds early, which is critical if you want to prevent them from going to seeds, and giving you 10x the number of weeds to deal with. This is one of the most important strategies in weeding, getting them before they go to seed or spread.
Another important strategy used by knowledgeable gardeners is to water the yard well a couple of times before the winter rains come, to encourage the sprouting of weeds. That give you the opportunity to pull them all up and eliminate them at an easier time getting rid of them in the winter, so they won't have a chance to grow the following year. This is especially important for wildflower gardens if your poppies are going to survive early spring competition from crab grass.
You can't get rid of all of the weeds this way, since some seeds will not sprout for various reasons, and other weeds spread by rhizomes, but it is a big part of the strategy that will minimize them.
In general, weeds tend to sprout where the soil is disrupted. If it is irrigated and fertilized, they'll grow even more, whether they are grasses, vines, shrubs or tree seedlings.
It is best to get them when the soil is moist, and temperatures are low. There are many strategies, and tools to help.
You can just mow your lawn and ignore the weeds, or hand pull them of course. Some people will use "weed and feed", which uses chemical fertilizers, while applying herbicide aimed at certain plants. The herbicide in this mix is usually 2,4-D, or dichlorophenoxyacetic acid, which targets the hormonal system of the weed. In dandelions, for example, it basically causes the plant to grow itself to death, like a cancer.
Under trees and hedges
Rakes and hoes are good bets for crab grass under fruit trees or hedges. The hula hoe, also known as the stirrup hoe, can clear a weed-clogged fence border fast. A worthwhile investment if you have these types of beds. For less soil disturbance under a fruit trees, you can use a hard-tonged bow rake.
It's best to weed by hand in a flower bed, and especially in a wildflower bed. Tug at the root crown, to make sure you get the root, and try to disturb as little soil as possible. For deep taproots, like that of the dandelion, a long slender tool like a weeding knife or a long screwdriver is best, though a garden fork can also be helpful. Push the fork down the root line, wiggle it a little, then tug the weed up with the root hopefully intact. A screwdriver will also work well getting weeds between pavers, flipping the weeds out with it.
Bermuda grass is one of the hardest weeds to eliminate, but it can be done. If you are willing to resort to chemicals, you can clear large areas of Bermuda grass with the herbicide glyphosate, sold under the brand name Roundup, but it will also kill other plants. For getting rid of it in mixed garden beds then, weeding by hand is the safest route. Using a pick or small shovel will be very helpful in attacking larger patches, and combining the two might work best. Try to dig up a patch as a whole, with the rhizomes and tendrils intact, so as not to leave many little pieces of rhizome in the ground. Each little section you leave will sprout into a new plant. Get at these new plants as soon as possible, and dig them up whole. In other words, follow the tendrils with your fingertips, tugging as you go. New shoots usually come out easily. Where the tendril snaps, you've reached the established roots, where you have to dig deep to get the missed root. If you don't have time to do the deep weeding, at least yank the easy new growth off to starve the hard-to-reach roots. Be certain NOT to put any of the Bermuda grass in the compost, or it will most likely survive and resurface. Put it in the city compost bin if you have one, where it can be professionally destroyed then composted.
Some plants that are commonly considered weeds include:
- Broadleaf plantain
- Creeping Charlie
- Leafy spurge
- Milk thistle
- Red sorrel
- Wild carrot
- ↑ ISBN 0-7167-1031-5 Janick, Jules. Horticultural science. San Francisco: W.H. Freeman, 1979. Page 308.
- Weed Identification Guide from Virginia Tech (Southeastern United States)
- Common weeds of the northern United States and Canada from Canadian Weed Science Society