Green Thumb Tip #15: Conquer the Weeds

Asclepias, milkweed,  July 2017

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What is a weed, anyway?

The gardener’s answer observes that any plant growing where you don’t want it to grow, is a weed.

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Dandelion, Taraxacum

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Some ‘weeds’ came to North America as invited guests, because they were beloved and useful to earlier immigrants.  Although many of us cringe at dandelions cropping up in our lawn or veggie plot; dandelions, Taraxacum species,  were originally planted in the veggie plot for their nutritious leaves, and have been used through much of human history as a medicinal herb.

Since most of us don’t use dandelions anymore, and they crop up where we least want to see them; we consider them a weed.

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Vinca minor, periwinkle, was brought to North America with European settlers.  It is now considered invasive, though many gardeners still buy and plant it.

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Other ‘weeds’ are actually native plants.  If you notice purple violets in your lawn, will you admire them or destroy them?  You can buy pricey violets, Viola odorata, from many native plant nurseries, if you aren’t fortunate enough to have them already popping up here and there on their own.  Other common native ‘weeds’ in our garden include pokeberry, Phytolacca americana; ground ivy, Glechoma hederacea; and wild strawberry, Fragaria virginiana.

Plants may be ‘wildflowers’ to some, ‘weeds’ to others.  Maybe it depends on whether they grow on a roadside, or in your own garden.  Native plant enthusiasts are sometimes accused of planting ‘weeds’ in their yard when they cultivate Asclepias or wild Ageratum.

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Aralia spinosa is a native tree with thorns on its trunk and branches. Because it spreads its seeds and sends up shoots from its roots, many consider it a weed to be eradicated from the garden.  Here it grows with native pokeweed.

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The same tufts of grass I’m digging out of my garden paths may be planted and coddled in my neighbor’s yard.  The seedling Rose of Sharon shrubs I’m digging out of my flowerbeds, may be valuable when transplanted into another spot in the garden.

Some ‘weeds’ now considered ‘invasive’ started out as desirable imported plants.  But, without the competition or predators that keep them in check in their native lands, they run amok here.  When birds carry their seeds around, or they propagate clonally; these once desirable plants colonize real estate and out-compete the natives.  This has happened with autumn olive shrubs, Elaeaganus umbellata; perennial Lantana, and  even the beautiful Bradford pear.

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Perennial Ageratum, Conoclinium coelestinum

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Periwinkle, or Vinca minor, came to the United States with European colonists in the Eighteenth Century.  An effective evergreen groundcover, it blooms in spring with beautiful lavender or white flowers.  But it spreads aggressively!  I often find myself yanking it out by the handful when it creeps into my borders.  Its roots form thick mats, and can choke out other perennials.

So what to do about weeds?

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Three natives growing together in our front garden: Rudbeckia hirta; mistflower, Conoclinium coelestinum, and Obedient plant, Physostegia virginiana.  Each of these can spread itself to become invasive, and may need to be ‘weeded’ out in early summer.

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‘Weeds gone wild’ can disrupt our garden plans.  They may shade out or choke out more desirable plants that we bought and planted.  They may compete for water and nutrients against our edible crops.  They might spread aggressively, colonizing large area with thick mats of roots and vegetation.

Well, before reaching for a handy toxic herbicide, take a moment to consider your adversary.  It helps to understand the plant you hope to annihilate!

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Morning Glory, or ‘bindweed’ sprouts each summer from seed, and grows through our bed of Lantana and roses.

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Is it a perennial?  Does it prefer sun or shade?  Does it root easily when chopped into pieces?  Does it have rhizomes or stolons?

Understanding its needs, and how it reproduces, helps you plan an attack.  Knowing how long it may live, and whether it will easily re-seed, tells you the scope of your problem.

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Self-seeding beauty berry crops up in our shrub borders, and out competes many other plants. It will grow several feet in a single season.

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Seeds may lie dormant for a long time before conditions are right for them to sprout.  Whenever you disturb the soil, you may be bringing long dormant seeds to the surface, giving them the conditions they need to grow.  That is why breaking ground to till or otherwise dig up new garden areas may bring ‘weed’ seeds to the surface.

Many weeds can be smothered, or prevented from germinating, or growing further, with mulch.

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While shredded bark mulch will suppress weeds, it may allow others to germinate as it decomposes.  The rogue Magnolia tree behind this bed is a volunteer, growing from the mulch.  Is there room for it to mature here, or must it be cut out?

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A relatively easy way to kill grass and weeds, without chemicals, when you want to start a new garden bed, is to simply cover them.   Use your choice of cardboard sheets, layers of newspaper (black and white only if you plan to grow food crops), paper grocery bags, burlap or landscape fabric.  Completely cover the area you plan to cultivate, and then layer compost, garden soil, shredded leaves, seaweed and even shredded bark mulch on top.  If you won’t be planting for several months,  add  ‘compostable’ materials like rinsed egg shells, fruit and vegetable peels, teabags and coffee grounds in your layers.  Some gardeners use straw as mulch, adding layers every year.  In my experience, there are always seeds which sprout, creating more weeds.

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Paper grocery bags covered with several inches of compost killed the grass and weeds under this new bed.  Pea gravel holds down the paper edges and serves as an initial border to the bed.  A loose layer of gravel on top serves as a light mulch to hold the compost in place as the plants take hold.

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If you are starting a new shrub border, you might add black plastic around the new shrubs, and cover this with mulch.  Black plastic may also be laid out over an area of grass and weeds you wish to kill, pegged down and left for several weeks.   The plants under the plastic are both smothered and cooked, leaving an area ready to cultivate when the plastic is removed.

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Colocasia ‘Pink China’ spread aggressively.  Now that they are established, I dig up plants each spring to share with friends to try to control how far they spread in the garden.

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Some weeds may be simply dug up.  If the weed is a desirable plant sprouted in the wrong place, you may dig it up and either transplant it or give it away.

Other weeds easily re-grow from any bit left behind.  Digging the plant today won’t destroy it; it will appear again in a few weeks.  In that case, cut the plant off at ground level and remove all of the stems.  This starves the plant.  You may need to cut it back several times before it gives up; but eventually, you will win.

Cutting weeds instead of pulling them up by their roots takes less of a gardener’s energy.  It also keeps the soil intact, giving no opportunity for new weed seeds to sprout.  You may cut weeds with a hoe at ground level, with a pair of scissors, or with secateurs.  It depends on the thickness of the stem you need to cut what tool you will choose.

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Plant densely, with many layers of plants, to suppress weeds.

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I like a Japanese Hori Hori digging tool for cutting weeds off at ground level, or for digging up plants to move.  It is a long, pointed blade with a serrated edge, which serves as both knife and narrow shovel.

Another approach is to simply mow an area several times during the summer to discourage perennial or woody weeds.  I often use a string trimmer a few times a year in our upper wooded garden, to cut back seedling trees and shrubs sprouting in an area where they can not grow.

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Plants just want to live and grow, like every other living thing.  And just because you begin a bed weed free doesn’t mean it will remain that way for long.  Seeds blow in on the wind and get deposited by birds.  Seed capsules explode and rhizomes creep.

As your organic mulch breaks down over time, it serves as a great medium for new seeds to germinate.  Any bare ground screams an invitation to colonize it with new plants.

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Evergreen ground cover, like perennial Hellebores, will shade out weeds so they can’t begin to grow.  However, Hellebores self-seed freely.  Large stands of Hellebores soon surround the original plants.

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Prevent new weeds by densely covering any planting area with desirable plants.  Cultivate the garden in layers, with plants of different heights, to make it nearly impossible for new weedy plants to get a start.  This would include some sort of perennial, maybe evergreen ground cover to protect your soil through winter.

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Rose of Sharon

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You might also consider using a gravel mulch.  Once a new bed is planted up, pile several inches of pea gravel over a layer of biodegradable material like paper or burlap, placed around the new plants.  The layer of paper or fabric stops perennial weeds from re-sprouting.  The gravel mulch doesn’t facilitate germination of seeds blown in to the bed.  You may need to employ some sort of border around the bed to hold the gravel in place, but this is a neat looking and effective approach.

Experiments with gravel mulch have demonstrated that shrubs and many perennials grow well through the gravel.  The soil remains cool and moist, and the pea gravel reflects sunshine back up onto the plant to reduce disease and increase photosynthesis.  This is an especially good way to conserve moisture in dry climates.

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Wild wood violets open in spring, carpeting parts of the garden in vivid color.  These perennial wildflowers may be considered weeds when they show up in a lawn.

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Some gardeners may still reach for an herbicide to zap the stray dandelion or wild onions in their lawn.  Few stop to realize the long term effects on their own health and well being, or on the ecosystem, from these toxic chemicals.  They penetrate into the ground and run off into creeks, ponds and rivers.   Many herbicides have proven links to debilitating and fatal diseases for anyone exposed to them.  Even if you wear gloves, you and those around you may still breathe in the fumes.  Is it worth the risk to your health, simply to kill a few weeds?

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With a bit of thought and a effort, weeds can be eliminated, and new ones prevented from growing, without doing any harm to yourself or to the environment.

After all, we are the gardeners.  Our goal remains to make the world a more beautiful and productive place.  We are happiest and most successful when we work with nature, and when we respect both ourselves, and the many life forms drawn to our gardens.

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Woodland Gnome 2018
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More information about health dangers of herbicides:

Weed Whacking Herbicide Proves Deadly to Human Cells- Scientific American
The Dangers of Glysophate Herbicide- Mother Earth News
New Studies Reveal the Effects of Glysophate – Mercola.com
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Ground ivy Glechoma hederacea

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“Green Thumb” Tips: 
Many visitors to Forest Garden are amazing gardeners with years of experience to share.  Others are just getting started, and are looking for a few ‘tips and tricks’ to help grow the garden of their dreams.

I believe the only difference between a “Green Thumb” and a “Brown Thumb” is a little bit of know-how and a lot of passion for our plants.

If you feel inclined to share a little bit of what YOU KNOW from your years of gardening experience, please create a new post titled: “Green Thumb” Tip: (topic) and include a link back to this page.  I will update this page with a clear link back to your post in a listing by topic, so others can find your post, and will include the link in all future “Green Thumb” Tip posts.

Let’s work together to build an online resource of helpful tips for all of those who are passionate about plants, and who would like to learn more about how to grow them well.
‘Green Thumb’ Tip #1:  Pinch!
‘Green Thumb’ Tip #2:  Feed!
‘Green Thumb’ Tip #3 Deadhead!
‘Green Thumb’ Tip #4 Get the Light Right!
‘Green Thumb’ Tip #5: Keep Planting!
‘Green Thumb’ Tip #6: Size Matters!
‘Green Thumb’ Tip # 7:  Experiment!
‘Green Thumb’ Tip #8  Observe
‘Green Thumb’ Tip #9 Plan Ahead
Green Thumb Tip # 10 Understand the Rhythm
Green Thumb Tip # 11:  The Perennial Philosophy
Green Thumb Tip #12: Grow More of That! 
Green Thumb Tip # 13: Breaching Your Zone
Green Thumb Tip # 14: Right Place Right Plant
‘Green Thumb’ Tip:  Release Those Pot-Bound Roots! from Peggy, of Oak Trees Studios

 

 

 

 

 

About woodlandgnome

Lifelong teacher and gardener.

2 responses to “Green Thumb Tip #15: Conquer the Weeds

  1. Lots of great tips – thanks!

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