Ecological Pest Control II: Soil Biodiversity

Where We Have Been

New readers  following my philosophy of organic pest control can click here for links to the entire series as well as for a brief synopsis of the argument as it has evolved in the four previous installments.


Friends, we have to talk about weeds.  Soberly.  Perhaps even tenderly.

Weeds can bring the hardiest of gardeners to tears; they can turn a reasonable adult into a tantrum-tossing two year old.  They can make a sanctified granny take the Lord’s name in vain.  Brace yourselves, because I’ve got to tell it straight-from-the-hip the way I see it: weeds are an integral part of a functional, maximally biodiverse ecosystem.  As such, they are also part of the organic gardener’s ecological pest-control tool-kit.

Nowhere is this more true than in our sprawling, monocultural urban and suburban wastelands where — by human intent — biodiversity has been systematically suppressed.

Don’t hate the messenger.  Please.  Let me explain:

Recall that biodiversity of life in the soil (a characteristic coveted by gardeners) emerges over time when soils remain relatively undisturbed.  Weeds stabilize soils and can improve them in a number of ways:

  • Weeds and their roots retard surface evaporation, slow soil desiccation, sequester water, help slow run-off and thereby prevent erosion.
  • Weed roots puncture and aerate heavy clay soils.
  • Weed roots forge channels in the soil, creating miniature subterranean river systems, thereby improving soil drainage.
  • Nitrogen fixing weeds extract atmospheric nitrogen from the air, and return it to the soil when they decompose.
  • Weeds generate organic matter.
  • Weeds overwinter predators, pollinators, and other beneficial insects.
  • Weeds give rabbits something to eat besides your hostas.

One way or another, and in varying degrees, organic gardeners need to let go of industrial agriculture’s and industrial horticulture’s obsession with weed eradication.  We have to make peace with the fact that weeds belong in the garden.


Wild strawberry is a useful weed. It inhibits soil erosion, overwinters beneficials, feeds wildlife and is easily removed when you’re ready to plant something more interesting in its place.

Soil-Friendly Weed Control

Weeding is a labor-intensive, ecologically violent, and ultimately self-perpetuating mechanical intervention.  The more you do it, the more you have to do it because it brings new weed seeds to the surface, or breaks off rootlets capable of generating whole new plants.  I don’t know about you, but I am no Sisyphus.  Long about mid-July when temperatures reach 100 degrees, I am more interested in sipping on a mint julep than I am interested in ripping up crab grass.


Weeds are a living mulch in which beneficial insects feed, reproduce and overwinter.

Wasted effort is not the real problem with weeding.  Our concern is pest control, plant health and the relationship between these and soil conservation.  Weeds are Mother Nature’s repudiation of the entire gardening project.  Every time you reach for your hoe, she sits up, sputtering, “Hey!  What are you–??  Are you out of your mind?  You’re about to break that!  Now you’ve gone and done it!  You’ve torn open the soil!  Look at the mess you’ve made!  Awww, now somebody’s gotta clean that up!  I guess it’s gonna have to be me!”

How can we, as organic ecosystem-ers, forge a useful working relationship rather than a traditional adversarial relationship with the plant life that arrives in the garden without invitation?

First, it really helps to know more about the weeds in your ecosystem than, “I didn’t put that there, it has to go.”  Knowing your weeds will help you make informed decisions about whether (and how) to tolerate, manage or exterminate them.  For example,  gardeners might be willing to tolerate weeds that are easily controlled by the shade of competing plants or shrubs.  Toward that end, it is fairly simple to create shade conditions that will suppress weeds by planting vegetables and ornamentals closer together than is the traditional agricultural, horticultural, and landscaping standard.

Many annual and biennial weeds can be controlled by dead-heading before the flower-to-seed cycle is complete.  Annuals and biennials die after setting seed.   Leaving the roots in the soil helps to prevent evaporation and erosion, it adds organic matter to the soil and improves soil porosity when the roots finally die.  The roots also prevent new weed seeds from surfacing.

Perennials weeds are trickier, but can be kept in check and even killed by keeping them cut to the ground.  Perennials are weakened and eventually die when they are forced to expend the sugars stored in their root systems on continual leaf growth.  Keeping them cut to the ground prevents photosynthesis and will starve the plant to death without disturbing the soil.  Mulching the stumps with the cut top growth will  return organic matter to the soil.  Once again, the roots remain in the ground intact, where they do work the gardener would have been forced to do using a mechanical intervention: they send tap-roots deep into heavy soils, improve soil drainage, slow run-off, prevent evaporation and erosion, sequester water, and bring deeply placed nutrients closer to the soil surface.  Where soil conservation is concerned, a pair of pruners, loppers, or a skillfully wielded sickle hoe are far better weeding tools than a garden trowel, or God forbid, a roto-tiller.

Weeds and the Gardener: Forging an Uneasy Détente?

As I’ve mentioned elsewhere, I do not practice no-till gardening, nor am I an advocate of allowing weeds to “naturalize” in an uninhibited way throughout the garden.  In my knotty-headed opinion, weeding is a useful mechanical intervention and has a place in the organic-gardener’s tool kit.

On the other hand, I am also of the opinion that unreflective weed antipathy and an eradication ethos enables unobservant, unaware, uninformed, inattentive and – dare I say it? – ecologically ignorant gardeners.   Here are a few questions I think every gardener should strive to be able to answer:

Close plantings of beets, lettuce, dill and carrot.  How many weeds in this photo do you know by name and habit?

Close plantings of beets, lettuce, dill and carrot. How many weeds in this photo do you know by name and habit?

  • What is the name of the plant that I am yanking up by its roots?  To what genus does it belong?
  • Which “weeds” in my ecosystem can I actually call by name and which ones can I not?
  • Did this plant I am yanking up by the roots arrive by wind, bird, chipmunk, or on the sole of my shoe?
  • Is this weed that I am yanking up by its roots an annual, a biennial or a perennial and how does it propagate itself?
  • Whom does this plant feed and/or shelter?
  • What roles do the creatures fed, sheltered or nectared by this plant play in my ecosystem?  What are their names?  Do they confer benefit, harm, or neither to my garden?
  • Why does this weed I am yanking up by its roots always appear here, in this particular location, and not over there in that one?
  • What environmental job does this plant (that I am yanking up by the roots) do?  What “need” does this particular species of plant meet in this ecosystem?
  • Who or what will do this plant’s job once I have yanked it up by its roots?  Can I substitute another plant to do the same job, or will I be forced to deploy a mechanical or chemical intervention to do it?

Bring your most present and observant Self to your garden ecosystem.  Bring your curiosity.  Take samples of your weeds, press them between sheets of wax paper, tuck them in a file marked “local ecology.”  Get a book on the plants that live in your ecosystem.  Identify your sample.  Learn about its life cycle.  To understand your ecosystem, you need to know the organisms that live in it.  Swim upstream against the comfortable inertia of not-knowing.

The Intolerables


Some weeds require an eradication philosophy, in my humble opinion.

There are, indeed, weeds that must not be treated “tenderly.”  Some are poisonous to pets or humans, or cause severe allergic reactions.  Some are allopathic – that is, they use biochemical means to suppress seed germination in (or outright kill) nearby plants.  There are also many feral invasives that are directly responsible for habitat destruction or the extinction of native species.  If you know your weeds, if you know your ecosystem, you will know when to deploy weeding techniques that prioritize soil conservation, and when to deploy weeding techniques that prioritize human, garden, and ecological health.

Be the Guru of Your Own Ecosystem.

Next time in The Ecological Tool-Kit – Hedgerow Biodiversity.  Stay tuned!


6 thoughts on “Ecological Pest Control II: Soil Biodiversity

  1. Laurrie says:

    A very interesting take on our relationship with weeds. Thoughtful (and humorous). All morning as I dug in a new area of the garden and turned up earth, all I could hear was mother nature complaining “now you’ve done it. Torn open the soil. Now I gotta get some weeds in there to fix it . . .” You really got inside my head with this post!

    (Mother nature also looks at our flowering perennial borders and thinks “it’s a fine prairie, but not enough grass in there.” I read that in Sara Stein)

  2. Thx for this very thoughtful essay on the role of weeds in our green spaces! Mother Earth News runs lists of common “weed” types from time to time and I’ve clipped them to remind myself what I’m seeing, where & why. We don’t do herbicides as you know, however, I do use the Grandpa Weeder on the dandelions (for the neighbors’ sake as much as anything!) In the backyard, I mostly leave the plantains, etc. for the bunnies. Come to think of it, maybe that’s one of the reasons we have so many bunnies!!!

  3. Kami Landy says:

    I LOVE dandelions in my pastures. I feel more at home with them there.
    For the moment, I’m trusting that there is more yummy grass than potentially dangerous- and not very tasty- stuff for the horses to eat. Later, I’ll worry about johnson grass and sicklepod and other potentially lethal visitors. And blackberries? They are NOT weeds!!! Yum!

    Lori Fontanes– thank you. I was just about to ask how to find out what some of those “just weeds” are. Even if they are not harmful, I’m always curious.

    And that pretty stuff that looks like water cress? I’ve GOT to find out if it is. Yum!

  4. Sho'Nuff says:

    This is the one I use… I think it is too pricey, but if you borrow it from the library and scan/photocopy sections of it that are relevant to your yard, it is a good tool…

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