A: Despite our concerns about summer water availability in 2001, late spring rains have provided plenty of moisture for weeds to flourish. No sooner do we turn over a shovel full of soil in the spring than up pop dozens, hundreds, or thousands of tiny weed seedlings ready to take over the most carefully maintained landscape. Many of these are annual weeds, like chickweed, that grow up, set seeds, and plant their seeds in one quick season. They don't have permanent roots but from some points of view their multitudes of seeds can be worse.
Let's consider the annoying common chickweed, but also some other annual weeds that give gardeners fits in the spring. Common chickweed, Stellaria media, spreads through abundant seeds. It can also live through mild winters rather than being killed out by cold.
The valuable book Northwest Weeds includes this pungent description of chickweed: "Common chickweed has many characteristics of the 'ideal' weed. It is an annual that very quickly grows from seed to seed-producer, and produces seeds continuously while conditions permit. The requirements for germination vary from seed to seed, ensuring that seeds do not all germinate at once, which would make the species vulnerable to weed control methods." (Ronald Taylor, Northwest Weeds, Missoula, Montana, 1990.) Taylor's small but comprehensive book is invaluable for identifying the invaders in the home lawn and garden.
The " ideal" weed keeps making seeds and the seeds come up at various times, so that the original plant can clutter garden beds with its kids, grandkids, greatgrandkids, and so on for generations, trying the gardener's patience with each generation. Obviously this is an ideal life from the weed's point of view, not the gardener's.
Learning a little about the habits of annual weeds will help in dealing with this one, as well as other annual weeds such as shepherd's purse (Capsella bursa-pastoris) and pepper cress (Cardamine oligosperma). Many of these annoying early-spring weeds were at one time eaten, and some are still added to wild salads. Pepper cress, shepherd's purse, and chickweed are all tasty at early stages of growth if sufficient viniagrette dressing is poured over them. (The more garlic, the better.) They were originally native to Europe and Eurasia and provided early spring vitamins needed for health. Like the dandelion, they were introduced to North America with settlers.
Be sure, when undertaking either to nibble or to control the weed that you have it identified correctly. No one, no matter how motivated, can eat enough chickweed to keep an infested garden clear of this pest.
Think of the management problem as a year-round effort. Try to prevent the just-germinated weeds from getting settled in and going to seed to prolong the problem. Scuffle hoeing the plants out will help to get you started.
But, as we noted above, lots of seeds remain in the soil. Every time the ground is disturbed by the hoe or any other tool, weed seeds rise to the surface, to the light they need for growth. The second step with annual weeds, after hoeing out the plants, is to shade out the new weed seedlings. Weed seeds often need light to germinate, so the object for control is to keep them shaded. Plants or mulch will do this. A vigorous ground cover that you plant can fill in to keep weeds down, although weeding has to proceed for a while before the ground cover does its job. Common vinca (Vinca minor) is one attractive ground cover. Avoid English ivy (Hedera helix) because it has become a troublesome invader to many natural settings in the maritime Northwest (and has been declared a noxious weed in Oregon as of spring 2001.)
Whatever you plant, provide water and fertilizer during the first season of growth for ground covers to encourage their growth. Choose waterwise groundcovers such as vinca, epimedium (bishop's hat), or even low evergreens like Cotoneaster dammeri.
Mulches, covering the ground with a barrier, can help to prevent the regrowth of the millions of seeds that will remain in the soil. After cultivating and hoeing, spread 2-3 inches of any weed-free organic mulch over the ground to prevent sun from reaching the seeds. Then it's necessary to control weed seeds that blow in on top of the mulch. But in a mulched garden, the weeds are easier to see as they sprout. Organic mulches look good and provide considerable weed control, but will need replacement as they break down.
If a fairly permanent control is needed in a shrub or tree border, use a woven "weed-blocker" mat fabric. These synthetic fabrics improve on the old black-plastic barrier. They allow water and fertilizer to penetrate to existing desirable plant roots. They are covered with a mulch after being spread on the ground. These weed barriers are useful where time for maintenance of the area is very limited and they will last for several years.
Annual weeds make seeds and often aren't easy to control with herbicides. Indeed, using a leaf-applied herbicide like glyphosate (RoundUP) doesn't make sense with annual weeds (though it's useful for perennial weeds that grow from the food reserves stored in roots.) When hit with an herbicide, annual weeds may have one plant killed, but the seeds remain to plague the gardener.
Advertisements often indicate that weed-killers can be applied to prevent the emergence of annual weeds. Some herbicides like dichlobenil (sold as Casoron and with other brand names) do provide pre-emergent control, keeping seeds from germinating. These products must be used very carefully, because they can easily inhibit growth for desirable plants and can pollute water if washed off landscapes.. Read and follow the label exactly. These products aren't appropriate for any area where crops will be planted often, such as flower beds, or vegetable gardens, because they will prevent growth of all plants, not just what the gardener wants to prevent. They will keep spring bulbs from growing properly if spread over underground bulbs. These pre-emergent herbicides are difficult to use effectively and safely.
Weed management isn't something that's done once a year, but is a constant effort requiring persistence and organization. This may be a bit too much like many other life-efforts to be comfortable, but it's fact!
Hortsense: Managing plant problems with Integrated Pest Management