Weeds are literally everywhere underfoot, which makes them a perfect object of study.
Wherever ground has been disturbed and opened up, a characteristic team of plant species moves in. If this ground happens to be our lawn, garden or farm, these plant species are thought of as "weeds" since usually we don't want them there. In cities, weeds thrive in open lots, parks, sidewalks and even roofs. Many weeds are now world-wide in distribution because they have been carried with humans from continent to continent. Certain plants can also be invasive weeds in natural areas such as forests, wetlands, prairies and waterways. Many of these species are recently introduced, non-native species. They spread rapidly because they lack predators in their new environment and have not established a competitive balance with the other species in the new environment. We will look into some of these invasive species later, but for now, let's focus on what characteristics make a weed so successful and who they are.
Plants that are successful as weeds have some (or sometimes all!) of these qualities:
- Reproduce in many ways; sexual (seed) and asexual (parts of the plant re-sprout)
- Produce many seeds
- Produce small seeds
- The seeds have fancy ways of getting carried around(float on air or water, stick to animals, many others)
- If you try to pull them they break off and re-sprout
- Roots or stems form rhizomes or runners
- They are hardy "generalists" and can live almost anywhere
- They grow fast (compared to crop plants)
- Their seeds may stay dormant in the soil for long periods
Can you think of other weed characteristics?
It is important to know which weed species you have and consider the characteristics of weeds if you are trying to manage them at low levels - can you see why? The IPM tactics you use to suppress weeds will also vary by the habitat in which they are found - you will not be able to use the same strategy on a wetland weed as a farm field or lawn weed.
Weeds, of course can also be beneficial. By growing quickly on open ground, they help prevent soil erosion. Tap roots bring up nutrients from deep in the soil. Some weeds are edible or have medicinal qualities. Weeds provide food and shelter for many animals.
1. Review or learn basic categories of plants (monocots, dicots; annuals, perennials)
2. Learn how these plants are sometimes "weeds"
3. Understand characteristics that make a plant a successful weed
4. Know weeds can be in any habitat
5. Understand that management tactics for weeds will vary by habitat.
•Weeds either indoors (potted or from pictures) or outdoors
•Books or keys on weed identification
•Diagrams of plant parts with names (especially if using a key)
Varies depending upon background on plants and how in depth you go.
One to several class periods.
If you can go outside,
1. Look at actual plants, with a picture book ID (e.g. Weeds; Golden Guide) and name as many plants as you can. Have them make observations on the plant itself:
how tall is it, what are it's roots like, is it flowering?
is it a monocot or dicot and how do you know?
is it an annual or perennial?
what habitat does it tend to occur in?
does it have seeds and if so what do they look like?
how does this plant spread itself?
2. Have students write down in their notebooks what weeds they found and draw sketches of the plants.
3. For older students, you can sample the weed population in an area by using a quadrant square at random intervals across a habitat and actually counting the number of plant species represented and their distribution within the square. (See Inventory and Sampling Weeds for techniques).
( Spring is a good time to do dandelions in the lawn out side and see flowering, pollination, tap roots, and some seeds by late May; Fall is a good time to see all kinds of seed in weedy areas.)
If you stay inside,
1. Have students brainstorm about plants or plant parts (seeds, stems, roots) that they can think of in their own experience. Ask if these plants are "weeds" or show the characteristics of weeds.
2. Make a list of the plants they have named and find references on these plants
3. Each student can report on one weed, describing it's harmful and beneficial aspects.
4. Have students "invent-a-weed" and report on it. In the report they describe:
the weed's name
appearance in drawing
habitat in which it occurs
characteristics (how it spreads, etc. from list above)
5. Think about how they would manage this weed (real or imaginary) if they did not want too many (review using IPM steps and tactics)
If you sampled an area for weeds, discuss with the students what you found there.
Were there only a few weeds or many?
Were there many different kinds of weed species or only a few?
Were they all clumped together or spread out evenly?
What characteristics of weeds did you observe in the plants you saw?
We know that weeds can sometimes be harmful to humans and the environment.
Can you think of reasons weeds can be beneficial?
Do you think the weeds found (discussed) today are helpful or harmful?
Can you think of ways we can prevent the spread of weeds from one country to another?
What are some IPM techniques for maintaining weed species at low levels?
Do these techniques vary by habitat?