8/8/2019 Weeds Science Factsheet

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WEEDS Science Page

DID YOU KNOW?Weeds are plants growingwhere they are not wanted.They can quickly grow and takeover bare patches of soil. Weedseeds can be buried in the soil

for many years. When they areuncovered, they can still sproutand grow.

Seeds ofeveningprimrosecansprout andgrow afterbeing buriedin the soil forover 100years!

WEED SEEDSMost weeds makelots of seeds.Weeds alsohave uniqueways tospread theirseeds.

Dandelionseeds haveparachutesthat float in

the wind.

WEEDS CAN BE FRIENDS...While weeds can become pests in fields, lawns, and gardens,they can also be useful. They can be used as food or medicinefor humans and animals. They can protect and improve thesoil. They can also be beautiful to look at!

Weeds quicklysprout and growon bare soil, andkeep it fromwashing orblowing away.

Deep-rooted weeds can bring up nutrientsfrom deep in the soil. When they die,weeds add organic matter to the soil.

...AND CAN BE FOES!It can be difficult to get rid ofweeds, especially in areaswhere humans havedisturbed the soil. Weeds canreduce crop yield in fields andgardens.

Where did all these

weeds come from?

Burdockseeds hitch aride on furand clothing.

Most weeds cangrow veryrapidly, andthey can growin manydifferent places.

gill-over-the-groundbugleflower

burdock

dandelion

evening primrose

Weeds compete with crops for space,water, sunlight, and nutrients.

lambsquarters

chicory

WEEDS ARE HARDY WEEDS GROW FROM PLANT PARTS

Manyweeds canalso sproutfrom roots,stems, orleaves.

A small piece ofstem or leaf ofcommon purslanecan grow into anew plant.

Field bindweedgrows lots ofroots. Newplants sproutup from theroots.

WEED LIFE CYCLES

Annual weedscomplete theirlife cycle in asingle season.

Seeds of

annualssprout andgrow intomatureplants.Aftermakingseeds, theplants die.

Biennial weedslive for twogrowingseasons.

During thefirst growingseason, they

make food thatis stored in theirundergroundstems or roots.In the secondseason, theyuse the storedfood to makeflowers andseeds.

Perennial weedslive year to year.

Perennials dieto the groundeach growingseason. Buttheir

undergroundroots or stemsstay alive andsend up newshoots at thestart of theeach growingseason.

Queen Annes lacelambsquartersyellownutsedge

Many weeds, such ascomfrey, have been used asfood and medicine forhundreds of years.

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8/8/2019 Weeds Science Factsheet

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CROSSWORDPUZZLE

Garden Mosaics is funded by the National Science Foundation Informal Science Education program, and bythe College of Agriculture and Life Sciences at Cornell University.

Across2. Grows where it is not wanted.5. Weeds can be ______ in gardens.7. A plant that lives from year to year.9. Completes its life cycle in one season.

Down1. Weeds have many ways to spread ______.3. Some weeds can be

used as ______.4. A plant that lives for two years.6. Some weeds can ______

from roots or stems.8. Weeds can reduce

crop ______.

1.

2.

3.

4. 5.

6.

7. 8.

9.

TRY THISWHERE DO WEEDS COME FROM?What you need

* about 4 liters (1 gallon) of soil from threedifferent places, such as a garden, an emptylot, a roadside, or a lawn

* 3 growing containers of the same size (about30 cm [1 ft] in diameter)

* hand lens* 3 popsicle sticks* paper and pencil* weed identification bookWhat to do1. Use a hand lens to search each soil sample

for weed seeds. Remove any large stones ordebris from the samples.

2. Punch drainage holes in the bottom of thethree containers, if needed.3. Place each soil sample in a container. Use

the popsicle sticks to label where they camefrom.

4. Place the containers outside or in a well-litroom. Water the soil in each container for afew days until some weed seeds sprout. Tryto identify the weed seedlings.

5. Count the number of weeds over a 4-weekperiod or longer, and measure the area ofthe soil surface in each container. Then

calculate the number of weeds per squaremeter (or per sq yard) for each soil sample.

6. Summarize your results on a chart and/or agraph. For example, you can put soil type onthe x-axis and weeds/m2 on the y-axis.

7. Can you think of a hypothesis for why moreweeds are growing per m2 in one type of soilthan in another? How might you test this

hypothesis?

CrosswordpuzzleanswersAcross:2.weed;5.pests;7.perennial;9.annual.Down:1.seeds;3.medicine;4.biennial;6.sprout;8.yield.

JOKEKnock! Knock! Whos there?Weed. Weed who?Wed know if you would answer the door!

SPOTLIGHTON RESEARCH

Velvetleaf Seeds Are Not All AlikeVelvetleaf is a large weed that produces

thousands of seeds. It can cost farmers millionsof dollars in lost crop yields. Scientists arestudying velvetleaf seeds, so that they can findbetter ways to control it. In one study, scientistsat McGill University in Canada tried to answerthese questions: Do large velvetleaf seeds

sprout (germinate) better than small ones? Doseeds from one plant sprout better than seedsfrom another?

They randomly picked 10 velvetleaf plants,and then collected up to 1000 seeds from eachplant. They separated the seeds from each plantby weightsmall, medium, and large. Then theyput the seeds in growth chambers. Inside thechambers, the moisture, temperature, anddaylight were similar to what one would findoutside in the spring.

More medium-sized seeds sprouted thanheavier seeds. Some of the heavier seeds

became dormant, that is, they may sprout atsome later time. The percentage sprouting alsodepended a lot on which plant the seeds werefrom.

The scientists believe that the differencesbetween seeds may help velvetleaf plantssurvive. Different seeds may sprout and growbetter under different conditions. The live butdormant seeds could be a kind of insurance forthe velvetleaf plant. Even if all the velvetleafplants in a field die off, the dormant seeds in thesoil could sprout later and grow into new plants.

Source: Baloch, H.A., DiTommaso,A., and Watson, A. K.(2001).Intrapopulation variation inAbutilon theophrastiseed mass and itsrelationship to seed germinability. Seed Science Research. 11, 335-343.

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