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Meet the weeds
"Know your enemy" is the watchword in war, and it works in the battle against weeds, too. Getting educated is the first step in becoming a garden-variety expert on weeds. By knowing their general habits, you'll be able to take a more informed approach to keeping weeds out of your yard—or inviting them in, if you choose. In this chapter you'll learn what defines a weed, and why these plants can be so infuriating. With an understanding of their different styles of reproduction and the many tricks they use for seed dispersal, you'll be able to adapt your gardening methods to keeping weeds at a minimum. You'll also discover that there's a "good guy" side to some of the most despised weeds.
What is a weed?
"Weediness" is in the eye of the beholder. The word "weed" is an epithet of purely human invention; in the botanical world, it simply doesn't exist. Silky red poppies and true blue cornflowers are treasures to cottage gardeners, but to wheat farmers, they're nothing but infuriating invaders that mar the harvest. Dandelions in the lawn have spawned an entire weed-killing industry, but to wild foragers, they are a welcome spring salad green.
A few weeds are so widely scorned that it's hard to argue with their classification. The clinging burrs of burdock, the ubiquitous clumps of chickweed—surely they have no redeeming value? Ask an herbalist, and you'll get a surprising answer. Burdock root has been used in herbal medicine for thousands of years, and chickweed was once depended upon as acure for the condition delicately called "irregularity."
The simple answer is that a weed is a plant out of place. When a plant interferes with the tidiness of our flower gardens, the sweep of our lawn, the size of the harvest, or even our personal well-being, it's a weed.
We're accustomed to visually attractive form and eye-catching flowers. A few weeds, including the statuesque, flannel-leaved mullein, are pretty enough to catch anyone's eye, but most weeds are easily overlooked. They may be tall and leggy or skinny and spindly, or crawl close to the ground, and most have tiny flowers that go unnoticed by everyone except bees, butterflies, and other nectar seekers.
Weeds become pests because of their adaptability and their abundance. These rugged plants also reproduce themselves so generously that it's a never-ending struggle to stay one step ahead. Most successful weeds have a number of the following characteristics to thank, though luckily, very few have them all:
Longevity Seeds with great longevity that germinate in a range of conditions, welcoming or otherwise.
Germination Discontinuous germination to prevent all seeds from sprouting at once.
Seed Rapid growth and the production of very large amounts of seed.
Dispersing Efficient means of dispersing its seed; strong, hardy growth, competing with the surrounding plants.
Chemicals Poisoning the soil with chemicals that are released from the roots.
Resistance Greater disease resistance.
Withhold water from your vegetable garden, and within a week or two your plants would be sending out distress calls, then keeling over and giving up. Most of our ornamentals, too, flourish only in certain settings or conditions. We buy perennials and shrubs for clay, sand, seaside gardens, or city lots, following the advice to select plants to suit our site. Our native wild plants are just as persnickety. Walk through a Massachusetts wood in April and you'll nod to trilliums, hepatica, bloodroot, and other Easterners. Take a walk on vacation in Arizona, and you'll meet none of your familiar plant friends.
Except for weeds. Queen Anne's lace decorates summer roadsides from coast to coast. Dandelions are a sign of spring across the continent. Farmers fight thistles in Texas and Pennsylvania simultaneously.
Exactly where weeds get their ability to adapt is open to endless discussion. One big clue that helps us explain why they seem able to rule the world is that nearly all of them actually came from somewhere else. Most weeds did not evolve in this country, slowly developing over eons the preferences for soil and weather patterns that, for example, make the cactus impossible to cultivate in Minnesota. Being foreigners, they also frequently lack the natural insect and disease enemies that would otherwise help to maintain the balance of native plant life.
That rugged constitution, combined with a dearth of biological controls, gives weeds a distinct advantage over our more mild-mannered garden friends. Add their super reproductive powers to the equation, and it's a wonder that we have any lawn or garden left.
LIFE CYCLE OF WEEDS
Understanding how weeds grow is key to controlling them—or cultivating them, which as you'll discover, can make them a striking and gratifying addition to your gardening. Start by thinking of weeds as plants: just like the invited guests in your garden, weeds are specialized by season, and sprout and flower in various cycles.
Annual weeds Germinate, grow, flower, and die in a single year. Chickweed, beggarticks, and ragweed are among the many annuals, all of which usually set massive amounts of seed for following generations.
Ephemerals Complete several life cycles in one year, germinating, flowering, setting seed and dying, closely followed by the next generation. Shepherd's purse, chickweed, groundsel, and bittercress are ephemerals. They produce less seed than annuals but have just as many offspring.
Biennial weeds Germinate and grow only leaves their first year, gathered in a cluster called a rosette. The following year, a flowering stem emerges; the plant blooms, sets seed, and dies. Queen Anne's lace and mullein belong to this category. They may produce prolific seed, or a more moderate amount.
Perennial weeds Just like your garden perennials, a dandelion lives on year after year. So do pokeweed, many clovers, and ground ivy. Their first year after sprouting, perennials produce only leaves; bloom follows in the succeeding years.
Seasons of growth
Weeding is a three-season occupation (or four, if you live in a mild-winter area) because weed seeds sprout at various times of the year. Time your weeding to their emergence, and you'll eliminate thousands of future problems with each swipe of the hoe. It's interesting but not essential to know which weeds tailor their growing cycles to which season. Some experts classify weeds into two broad categories: "warm season," for weeds which sprout in spring and summer and flower summer to fall; and "cool season," for weeds which germinate from fall to early spring, then grow and flower quickly in spring.
Other sources save these categories to apply only to annual weeds, calling them "cool-season annuals" or "warm-season annuals," since biennial and perennial weeds are usually evident at least three seasons of the year. The terminology isn't nearly as important as a basic awareness that there are two main seasons when weeds appear: fall to early spring and spring to summer. As always, the most important antiweed rule is to get them out before they set seed or spread rampant roots.
The flush of green seedlings that arise in fall through late winter are the start of the cool-season weeds, which sprout when the soil is chillier than 60°F. When the air warms up, cool-season annual weeds like henbit, purple dead nettle, and chickweed take off like a rocket, hurrying to bloom and set seed before heat does them in. Dandelions, clover, and other perennials whose bloom peaks in spring may also be considered cool-season weeds, of the perennial persuasion. In fall, remove annual weeds when you see them sprouting and evict established perennial weeds, and you'll have a head start on the following season (see pages 152-159).
In late spring through summer, the warm-season weeds come into their own. Now the soil is filled with seedlings of crabgrass, foxtail grass, and purslane, which germinate when the soil warms to above 60°F. Because garden plants are sprouting or growing at the same time, these weeds are best discouraged by mulch or hand weeding. Pre-emergent herbicides also can discourage the summer flush of warm-season lawn weeds (see pages 160-163).
One of the most distinguished characteristics of weeds is their willingness to "go forth and multiply." Their highly successful techniques are generally variations upon one of two basic methods—seed or spreading roots—although some weeds may use a two-pronged attack. Understanding how weeds propagate themselves can be key to controlling them. In the weed directory (see pages 18-129), a fact file is provided for each weed, detailing its propagation technique.
Annual weeds are the chief offenders when it comes to producing more seed than any gardener could want. But perennials believe you can't get enough of a good thing, too. Just one dandelion plant holds the power in its innocent yellow flowers to generate more than 15,000 seeds each year. A single plant of purslane takes it to an even greater extreme, ripening as many as 50,000 seeds in a single summer.
Not all these seeds fall on fertile ground, thank goodness. Birds, mice, and other seed eaters take a big share, and other seeds may land on concrete or other inhospitable sites. Still, with all that potential piling up year after year, it's not surprising to hear that every handful of soil holds thousands of weed seeds, just waiting for their chance to sprout.
If seeds are a means of propagating in the future, roots are a method for the present. Vegetative spread occurs in one of four ways—through stolons, runners, rhizomes, or roots. Stolons and runners are both creeping stems that sprout above the ground and then send down roots. Stolons are often in branch form, and may root before they even hit the earth, as in the case of the blackberry bush. Rhizomes are underground stems of the type produced by couch grass, nettles, ground elder, and hedge bindweed. They usually grow close to the surface and have small buds along their length that leap into life should the growing point be snapped off. Some thistles and field bindweed send out horizontal roots to multiply, which can produce new buds at any position along their length. Finally, plants with deep taproots, such as dandelion and dock, despite relying principally on seed dispersal, will also regenerate themselves if their roots are cut up.
Seedling weeds may look like an advancing army, but they are easy to dispense with. You can hoe them off or bury them alive in just minutes. Weeds that increase their territory by spreading roots, however, include some of our most insidious garden pests. In most cases, only the painstaking removal of each creeping underground stem or root does the trick. Even chemical controls find Bermudagrass and other spreaders a tough battle (see pages 160-163). The best approach is to monitor your yard and garden. Should a notorious spreader show up or leap to another part of the yard, remove it completely (see pages 158-159) as soon as you see it, and dispose of all pieces in the trash. After weeding out a spreader, watch closely for any signs of regrowth and have another go at it. Often the only solution is to remove the desirable plants from a bed and dig deep to evict all traces of the invader before replacing those plants you want.
Most seed-producing weeds have evolved masterful methods of dispersing their produce, many of which are opportunistic in character. All kinds of helpers spread the growth of weeds—most of them unintentionally, and others by design. Herbalists, gardeners, and even the U.S. Department of Agriculture have all been responsible for weedy plagues, although the plants were dispersed with the best of intentions. But in most cases, weeds depend on innocent helpers to get their seeds to a bit of welcoming ground.
Seeds with fuzz, silky hairs, or wings on the seed coat are all designed to go with the wind. Many weeds go one step further and actively shoot their seeds out once they are ripe. For example, oxalis, hairy bittercress, and ground elder all give their seeds a little carefully-timed boost. There's no way to ward off wind-blown seeds, but you can get rid of the plants before they release their seed (see pages 152-163).
Aquatic weeds (see page 171) depend on water to carry along the next generation, snug in their waterborne seeds or through bits of plants ready to root. But land weeds, too, can spread by waterways. Purple loosestrife is the cautionary tale here; its seeds ripened in gardens and then were carried by wind and (rivulets of) rain to streams and lakes. Since a single purple loosestrife plant produces millions of seeds, it's no surprise that many waterways are splashed with purple. Water also transports the largest seed in the world, the coconut, since it can float on water to sow coconut palms on distant shores.
Our feathered friends are responsible for many of the weeds in our yards. Weeds offer nourishing seeds and berries, and at least some of those pass through the avian digestive system unscathed. Deposited with a dab of "fertilizer," the seeds of mulberry trees, poison ivy, ragweed, pokeweed, and many others suddenly spring up in our lawns or gardens, even though the parent plants may be far away.
Woodpeckers, jays, nuthatches, and other birds cache seeds for eating later. Not all of these seeds go down the hatch, and those that make their way to soil can crop up as weeds. If you keep a bird feeder, you already know about the delights of unexpected sunflowers, which spring up wherever a bird drops a seed.
Diet and fur or feathers are the two ways animals spread weed seeds. Like birds, your backyard mice, raccoons, deer, and other animals may gift you with deposits that contain the start of weeds. Squirrels plant "weed" gardens in the fall, burying acorns and nuts that pop up into seedling trees that are usually unwelcome in our gardens. Far more frequently, weed seeds travel in the fur of wild animals, farm animals, and our beloved pets.
"Hitchhiking" is one of the most ingenious devices for seed dispersal, and many weeds make the most of it. Comb the burrs from your dog's ears, and those that fall to the ground during the grooming operation can easily start a plantation of burdock or beggarticks. Guard against an invasion of weeds by grooming pets indoors, where you can sweep up and dispose of the weed seeds you comb out.
The hooks and barbs that give weed seeds a grip in animal fur or feathers can also latch on to our clothes on an outdoor jaunt. Burdock is easy to steer around because its wayfaring seeds are big and noticeable, but other weeds are much more surreptitious. The seeds of Queen Anne's lace, for instance, can cling to a careless sleeve by the dozens. Weed seeds can also come home in the tread of your boots or glued to the grill of your car. Just use a little common sense when you clean up after an outdoor adventure, and avoid dropping weed seeds where they could cause you labor later.
Excerpted from Weeds friend or foe? by Sally Roth. Copyright © 2002 by Sally Roth. Excerpted by permission. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.