Minimize Soil Disturbance
There are a number of effective techniques for reducing annual weeds in the flower bed. These techniques either break the reproductive cycle of the weeds already on your property, or they keep new weeds from getting into the area in the first place.
The best way to control annual weeds is to prevent them from emerging. That means minimizing the distrubance of the soil and then mulching the garden beds very well. You minimize disturbing the soil because there are 20,000 to 30,000 weed seeds under every square foot of your garden bed just waiting to be exposed to light so they can germinate. Every time you dig a hole to plant another perennial, you are exposing hundreds and thousands of weed seeds to likely germination if nothing is done.
We assume that the first time you establish the bed or garden you must dig it up and perhaps even rototill the area to get the soil prepared. After that you should have the whole bed covered with 3 to 4 inches of organic mulch all year round. From then on you disturb only that portion of the bed where you are adding a plant, planting some seeds or bulbs, or transplanting a plant.
Mulch to Control Annual Weeds
The absolute best way to solve an annual weed problem and prevent it from ever coming back is to use a layer of organic mulch during the entire year. Mulch does a number of good things for the flower garden, and weed control is one of them. A 3 to 4 inch layer of wood chips, pine needles, chopped leaves, or shredded bark mulch over the surface of the growing bed prevents almost all annual weeds from getting a chance to even germinate. Those few weeds that pop up through the mulch where landscape plants protrude are easily pulled by hand.
Pulling Annual Weeds
Routinely pull a few weeds each visit to the garden beds and the weed pulling never becomes an overwhelming task. Try to get rid the garden of annual weeds within the first 3 weeks of their emergence, before they have a chance to develop seeds. Weeds are easiest to uproot right after a rain, when the soil is damp. It is important to pull up the roots, rather than just breaking off the stem. Grasp them between the thumb and forefinger down at the base of the weed at the soil. Pull slowly and steadily, rather than jerking the weed abruptly out of the soil. As the season progresses, the number weeds appearing should diminish.
In fact, pulling up all the annual weeds that appear in a season will result in only about half as many weeds the next year, and half again the third year, assuming the bed stays mulched all year long. In two to three years you will have almost none. The key is keeping the mulch at least 2 inches thick all year.
No Fall and Spring Cleanup
This section goes against the advice in almost every garden book ever written. They all recommend that in the fall and again in the spring, you rake off all the mulch and debris in the flower bed and put all that stuff back on the compost pile. The rationale is that you will be gathering up many of the pest insect eggs and disease spores and therefore would expect to have fewer insect problems and disease problems next year. Actually the opposite is more likely the case.
When you rake up a 2 to 3 inch layer of organic mulch that has been on the bed for say six months, you destroy the habitat of all the spiders, ants, and beetles that make up the most important part of any pest insect control system. Those three groups of insects will control pest insect eggs far more effectively than we can. You also destroy the microbial population of bacteria and other critters inhabiting organic mulch. Among their roles is the control of disease spores. The practice of fall and spring cleanup comes from commercial agriculture which in fact does need to follow that system. Think about how nature handles life in the woods. Does Mother Nature come by every year in the woods with a fall and spring cleanup? No.
At the same time, we are not suggesting that you don’t cut back your perennials, and remove sticks and other unsightly debris that has collected in the bed during the season. Just leave the mulch alone or better yet, add a fresh layer.