I have an elderly neighbor who neatly fits the "Crazy Cat Lady" profile. Of the thirty of so felines thronging her porch, she says, "Oh, they’re not mine. I just feed them." Spring and fall, year after year, kittens become cats, cats beget more kittens and the feral colony expands.

Gardeners who struggle each year to control weeds suffer from an analogous syndrome. Quite unintentionally, they raise huge "litters" of weeds every year, viewing the annual onslaught helplessly, an inexorable force of nature, rather than a process abetted by their own behavior. As with kittens, good family planning is clearly more enjoyable than letting weed populations explode.

annualgrasses copyOf course, control of weeds is more challenging than for kittens, not least because many plants aren’t limited to reproducing by seed. While it doesn’t sound very fun, a huge subset of weeds can propagate ‘asexually’ (or clonally.) Plant scientists refer to them as ‘pernicious’ because they have subtle and reliable means of multiplying from bits of roots or bulb-like nodules in the soil. And a Plant Parenthood approach to weed control is woefully inadequate if your garden is situated such that weeds seeds blow in from other sites (as are most farms) In theses cases, brute measures may be necessary.

Imagine for a moment what a botanical census of your garden would show, if one could count every seed and dormant root. In open ground, in areas not covered by a thick layer of mulch or groundcover, are thousands of seeds, waiting for optimum conditions to sprout. Over the course of the spring, as the ground warms, the first cohort to express itself are the annual grasses. If you wack those grasses down, a new crop will sprout, along with a different cohort of tap-rooted daisy-like flowers and thistles. Few can resist the instinct to wack them down again. With the sunlight now penetrating the surface of the soil, another cohort emerges—the ground-hugging bur clovers, morninglory, and cranesbill. And, as soon as you turn your back, the tap-rooted plants have sprung up again, along with another crop of grasses. The situation does appear hopeless, as long as you regard weeds as an undifferentiated rabble. The two classes of weeds have very different behavior, requiring different strategies.


Although at first glance the towering stands of annual grasses appear intimidating, they are in fact the easiest class to eliminate. Each year, annual weeds grow, produce thousands of seeds and die. The seeds will germinate over a period of many years: “one year’s seeds, seven years of weeds” is an accurate but misleading garden aphorism. While it is true that any given crop will germinate over a long time period, the vast majority will sprout in the first year. By preventing this year’s weeds from producing seed, you’ve reduced next year’s potential population by over half.

nodding grassWith many annuals and grasses, you can achieve this by flailing (.k.a. ‘weed-wacking’) as soon as you see the plants flowering. (In the San Francisco Bay Area, this can be as early as March.) Although grasses have true flowers, being wind-pollinated --achoo!-- they’re not showy, so it can be a challenge to know when they’re about to drop their seed. For the most common weedy annual grasses, the flower heads nod as the seeds mature. After the seeds have dropped, flailing won’t help control the weeds. Depending on the rainfall patterns, several crops of annual grasses may appear in the spring, but the first crop is the largest.

If a landscape has been neglected for several seasons, it is likely heavily infested, so it is best to ‘pre-sprout’ the remaining weeds, by giving the area overhead water and allowing several new generations of seeds to germinate. For large gardens, this is usually accomplished by first roto-tilling. It is critical that when each new cohort of weeds sprouts they be removed by light hoeing, leaving the pulled weeds on the surface as a mulch.


During this process, you’ll see a dwindling number of annuals and grasses, but you should resist the urge to declare mission accomplished, for this is the point that the class of weedy perennials will start to thrive. Like Tribbles, perennial weeds are essentially born pregnant. Most are deep rooted and will grow back if even a fragment of the root is left in the soil.

cardoonIn the spring, when the soil is still moist, some of the tap-rooted varieties can be ‘grubbed’ (dug out with the roots) using a long spading shovel, but diligence is required, since any piece of root left in the ground will regenerate.

In short order, you’ll understand why these weeds are called pernicious. Morninglory routinely challenges the fealty of commercial farmers to organic farming principles. To establish a landscape, careful spraying can be both practical and conscientious.

The most widely used herbicide, glyphosate (Roundup), is often vilified as a pesticide, without considering the relative hazard of a chemical with a mode of action morninglorythat targets plants vs. insecticides, many of which are based on nerve poisons. The invention of glyphosate has been compared to the discovery of penicillin; certainly, it revolutionized agriculture, but, as with antibiotics, has been abused by overuse. Judicious application of limited quantities can stop a weed invasion while still allowing untreated trees, shrubs and annuals from seed to thrive. After a landscape is established, only minute quantities will be needed, if at all. Routine spraying on a maintenance basis is probably a good indicator that a weed control program has failed.


Most annual weeds sprout on the surface of the soil, so a heavy mulch will suppress some of the seeds. (Always leave a portion of your garden unmulched, to promote ground-nesting bees and other alternate pollinators for your orchard and vegetable crops.) But unless your mulch is very hot, a portion of the seeds remain viable. And if your goal is to grow anything from seed, mulching will prevent those seeds from sprouting, too. When choosing a mulch, select one with a mixture of bark, wood and leaf material. Arborists’ wood chips are ideal. Commercially available bark mulches are not only a product of industrial logging practices; they are not easily incorporated into the soil, and can create a ‘hydrophobic’ effect that actually repels water. Equally unfortunate, this is also an ideal environment for Argentine ants, which love to build shallow nests in dry soil.


If you are starting with a site with heavy weed infestation, you should begin purging the seeds prior to planting. The first line of defense against weeds is to make sure they NEVER go to seed. The process requires four initial seasons of diligence, but will reward you in the years that follow with dramatically reduced needs for maintenance.

(1) Flail (weed-wack) the first weeds as they sprout in the spring, before flowering.
(2) Wait for re-growth, spread soil amendment and roto-till into the soil before the weeds flower
(3) If the spring has little rainfall, promote regrowth by overhead watering
(4) Wack, re-rototill, or hand-cultivate as weeds germinate
(5) Plant shrubs and trees
(6) Apply a thick layer of mulch in planted areas. For areas where you will be growing plants from seed, continue overhead watering, removing weeds as they appear, or spot-spray for pernicious weeds.

Of course, there will always be a few escapees, but these can be removed by hand-cultivation or, more rarely, spot spraying.

Once the annual and pernicious weeds are no longer overrunning your landscape, you can introduce native annuals and perennial grasses. For these desired plants, you’ll want to promote propagation, so will leave them until they shed their seeds. Over just a few years, a single successful flower will have thousands of progeny, and you’ll experience the abundance of spring wildflowers. Using the principles of Plant Parenthood, you can promote a joyful palette of poppies, lupine, toadflax and probably a few volunteers you’ve never seen before.