For gardeners, weeds represent one of our biggest challenges each growing season. These formidable foes are relentless in their quest to invade spaces and rob the plants we love of precious water and nutrients. Left unchecked, they are equipped to out-compete and shade out our garden plants and veggies, consuming the space for themselves.
Some basic understanding of weed life cycles can go a long way in the yearly battle to maintain our gardens and landscapes.
Weeds can generally be defined as plants that are growing in a place where they are unwanted. They can be found anywhere, from cracks in the sidewalk to the most well-manicured ornamental garden. All they need is soil, water and sunlight to proliferate.
Weeds do have common similarities that make them the highly competitive, relentless invaders we all detest. Most weeds are quick to establish themselves, flower rapidly, produce abundant seeds, have an effective mechanism for seed dispersal and thrive in adverse conditions.
The first step in effective weed control is identification of the weed. If you are like me, there are many times early in the season that I scratch my head when trying to identify the first tiny sprouts that are beginning to invade. There are many excellent weed identification books and websites available for assistance with identification. The University of Illinois Weed Science webpage (go.illinois.edu/WeedID) features great information about many of our most common problem plants.
Once identified, the next best information to research is the weed's life cycle to understand whether they are annual, biennial or perennial weeds.
Annual weeds germinate, grow and set seeds and die all in the same year. They are known to be prolific seed producers, often producing hundreds or thousands of seeds per year and rely on their huge seed bank to geminate again next year. Control is usually relatively easy, with the key to effectiveness centering on stopping seed production. Although they will die as winter's cold sets in, any seeds that were produced will proliferate next year's infestation.
Biennial weeds have a longer life span, requiring two years of growth to complete their life cycle and die. The timing of control can be a bit trickier as their susceptibility to control measures may vary based on their life stage. However, the goal of stopping seed production is still central to their control. Similar to annual plants, they rely on seed germination for a new batch of seedlings each year. Without an established seed bank, their populations can be eliminated over time.
Perennial weeds are perhaps the most difficult to control since they persist for multiple seasons regardless of seed production. Although they are not usually known to be heavy seed producers, they may have other means of multiplying their numbers from vegetative reproduction such as sending out runners (also known as stolens) along the soil surface. Each runner will produce a new plant as it sends roots into the soil and initiates bud development for above-ground plant parts.
Given their perennial growth and multiple means of reproduction, it really pays to understand these weeds prior to initiating control.
In addition to understanding whether a weed is an annual or perennial, it can also be helpful to study the timing of its life cycle.
For example, henbit (Lamium amplexicaule) is a winter annual prevalent in our area. It pops up in crop fields and vegetable garden beds very early and flowers in April each year. I always get questions about this plant from gardeners eager to stay ahead of weed issues early in the season. However, this plant completes its entire life cycle before the gardening season really begins.
Therefore, it really isn't one that I recommend folks control because its not a competitor with vegetable crops we plant later in the season and rarely exists in perennial garden beds. It's a rare example of one weed we can pretty much ignore and just enjoy the pretty purple blooms while they last.
If you need help with weed identification and control measures, don't hesitate to call our Master Gardener's Horticulture Hotline. Both the Champaign County and Vermilion County Master Gardeners maintain this service throughout the growing season.
Our Master Gardener volunteers work with you to identify your weed problem and recommend control measures to keep your gardens weed free.
Simply call our Champaign office (217-333-7672) or Danville office (217-442-8615) and Extension staff can connect you with Master Gardeners for help.
Ryan Pankau is a horticulture educator with the University of Illinois Extension, serving Champaign, Ford, Iroquois and Vermilion counties.