Weed Management

As I begin to work outdoors, my first focus is to attack the intrusion of unwanted weeds in my landscape. The war against the weeds begins anew each spring! I have often thought that the term “weed management” was rather unrealistic. But thankfully the Master Gardener classes have taught me some very useful facts about weeds, and I feel much more empowered in the battle. Here’s some information that will hopefully empower you as well!

We all have our least favorite weed(s). Mine are grasses like annual blue grass, creeping bent grass, and crab grass. These grasses show up everywhere in my landscape, and they are difficult to eradicate. Many people complain of bind weed (wild morning glory). For others, nut sedge or horsetail is the enemy. Sometimes, what is considered by one person to be a miserable weed, another person considers it to be an ornamental – like English ivy. Some plants are weeds in one instance and not another. Other plants are just simply obnoxious! They can be hazardous, a nuisance, or can cause injury to people, animals, or a particular crop.

The first step in weed management is identifying the plant. A little time spent with some plant reference material can give you some great ammunition for the battle! You don’t have to be an expert in botany to work through a weed identification book. Once you gain some key characteristics, you can make some intelligent decisions in how to best control that particular weed.

Photo of bull thistle

Common weed – bull thistle

An important key characteristic is the weed’s life cycle. They are usually annuals or perennials with a few that are biennials.

1)      Annuals: They go from seed to seed is less than one year. These weeds produce extremely large amounts of seed to keeps their species alive. There are winter annuals that germinate in the late fall through early spring, and they prosper without warm temperatures and sunlight. Examples of winter annuals are: chickweed, little bittercress and annual blue grass. Summer annuals germinate quickly in the spring and early summer and are aggressive. Examples of summer annuals are: crabgrass, pigweeds and lambsquarter.

2)      Biennials: Species in this cycle are less common. They take more than 1 year but less than 2 to complete their cycle. They would start from seed in the spring and grow through the summer, fall, winter and spring of the next year. In the second summer after flowering and producing seed they die. Examples of biennials are: wild carrot (Queen Anne’s lace), bull thistle and tansy ragwort.

3)      Perennials: These are often the most difficult to control because the plant’s underground storage systems survive the winter even though the above-ground parts may have died back. Many of these weeds are deeply rooted and spread from seed and also from roots, tubers, bulbs and rhizomes. Examples of perennial weeds include: bindweed, curly dock and dandelion.

Here are some methods of control to reduce the impact and spread of weeds:

Photo of dock

Common weed – dock

1)      The first weapon in the battle against weeds is tilling or hand pulling. A hoe and other tools are most effective on annual weeds that have shallow roots.

2)      Creating beds is another method of control. With beds, soil working is reduced so the weed seeds that lie dormant in the soil don’t get brought up to the surface as much and mulches are used extensively in-between the beds.

3)      Mulching is a wonderful weed suppressant for annual weeds. When bare soil is covered, many weed seeds don’t germinate or can’t grow through the mulch. Also, when mulching is used instead of tilling, weed seeds are not brought to the surface

4)      Irrigation that waters only the desired plants is a method of weed control. Weeds need water as well as the vegetables or ornamentals growing in the garden. Overhead sprinklers water a large area giving weeds what they need to grow. Managing water to just the desired plants reduces that amount of water available to weeds.

5)      Planting cover crops can help to smother out winter weed growth on annual flower and vegetable beds.

6)      Herbicides can be used selectively (for a specific type of weed like a broadleaf) or non-selectively (damaging to all plants). It’s very important to read the label on the herbicide that you’re using. The label is the law! When using herbicides, here are some things to consider:

  • Herbicides work poorly in dry conditions. Plant leaves have guard cells that regulate the passage of oxygen, water and carbon dioxide. During environmental stress the guard cells close so herbicides will not penetrate. To have the most effective herbicide application, water the area where the herbicide will be applied 24 hours before the application. Also, only apply the product in moderate temperatures.
  • Know the cycle of perennials. In the spring and early part of the summer, the plant sugars are flowing out from the roots to the foliage. If herbicide is applied when the sugar is flowing out, it very likely will not reach the root and effectively kill the perennial. In the spring and early summer, cutting the vegetative growth of the weed off will essentially starve the root as it will continue to have sugar flow outward to produce more foliage and flower. If herbicide is applied in the later summer and early fall when the plant sugar is flowing toward the roots and the plant is weakened from being starved, the herbicide has a much greater chance of successfully killing the root.

Having weeds in your landscape is inevitable. There will be some battles to keep the weeds managed, but knowing just a few key facts about the weeds that you’re dealing with will help to ensure that you’re the victor over the weeds!

Next week is spring break, and I’ll be spending time with my family. I will return shortly with another post from my Master Gardener class. Happy springtime everyone!

Question for the week: What is the worse weed in your landscape?


Weed photos from: http://cropandsoil.oregonstate.edu/weeds/

By Kimberly Bell

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