Controlling Annual Weeds


The gardener’s war on weeds cannot be ignored at this time of the year, as cool-season annual weeds respond to the current temperatures and recent rains. By popping up in our gardens.

The weeds in front of us always command immediate attention, but they also encourage a broader view of weeds. Let’s review the sources of the problem and the strategies for weed control.

The first step in control involves knowing the three broad categories of weeds: annuals, which are usually the most troublesome, and biennials and perennials, which we will consider on another day.

Annual weeds are those that grow and die in one season. This cycle begins with seed germination and ends with the dispersal of a new generation of seeds.

Annual weeds include two sub-categories: summer and winter annuals, which are also referred to as warm season and cool-season annuals. The names of weeds in each of these groups could be identified, but their botanical or common names are less important than their life cycle.

After Annual Weeds Sprout

Cool-season annual weeds germinate from seed in the late summer or early fall. They grow during the winter, flower, set seed and die from heat in the late spring or early summer. This approximate calendar guides actions to reduce weed growth in the garden. Right now, these pesky plants have already germinated, so the appropriate action is to minimize the production and dispersal of seeds. Do this by removing the flowers as soon as they appear. Depending on the circumstances and other factors, this can be done by plucking the flowers, mowing the weed batch, or pulling the entire plant.

Warm-season annual weeds germinate and grow in the spring, and thrive throughout the summer and into the early fall. They will die by frost, however, in the Monterey Bay area, where frost comes later if at all, these plants can persist for quite a while. Controlling warm-season weeds after germination uses the same techniques outlined above: minimize the spread of new seeds by removing the flowers or the entire plant before, or as soon as, the flowers appear.

Up to half the weeds that are pulled from the garden are still capable of dispersing seeds, so the safest plan is to dispose of them in the green waste. They could be added to a compost bin, but only if your compost maintains a temperature of 160 degrees Fahrenheit or more for three hours or more, the seeds won’t survive.

Before Annual Weeds Sprout

Methods to minimize the production and dispersal of seeds are highly recommended, but inevitably some seeds will make their way into in your garden. Seeds will arrive from weeds that already grow there, or are brought in by the wind, by the dropping of birds, or by hitching a ride on people’s shoes or clothing, animal’s fur, or imported plants, even plants from a garden center. The result of these several sources is the weed seed bank tat exists in all gardens.

All seeds require light and moisture to germinate, so the basic method for discouraging the germination of seeds already in the garden begins with mulch. Two or three inches of organic mulch will deny the seeds light, and most will not be able to sprout.

Viable seeds can remain in the soil for years, waiting for light and moisture. They might be surprisingly deep in the soil. The best plan is to let sleeping seeds lie. The worst plan is to dig up the soil to give the seeds access to light and moisture. If you need to dig up your garden, even to install a new plant, cover the exposed soil immediately after with mulch. Mechanical tilling of the soil will reliably produce a new crop of weeds.

In addition to mulching, close placement of desirable plants also will deny light and moisture to the dormant seeds. In many cases, a closely planted bed is also attractive.

Also, controlling access to moisture with drip irrigation, while controlling access to light with mulch and landscape plants should minimize weed growth significantly.

Finally, let a few weeds grow. You are unlikely with a goal of complete eradication of unwanted plants, and there is some value in the contribution of weeds to the flora and fauna of the garden. In any event, a casual (but systematic) approach to weed control allows you to relax in the garden.

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