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Weed Prevention Tips, Techniques and Q&A's

Many gardeners have questions about weeds and weed prevention. The themes below lead to common questions and answers about weeds, weed prevention and weed-free gardening.

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Weed-free gardening

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Weed-Stopping Strategies

Use Einstein's Approach: Stop the Insanity of Weeding
Hate Garden Weeds? Plant a Forsythia Bush
Why do weeds overtake gardens so fast?
Is it possible to ever "win the war" against weeds?
What's the Fuss About Forsythia?
Spot the 800-pound Gorilla in the Garden
How can I get the jump on weeds & minimize weeding all season?
Survey Figures Bring Gardeners To Their Knees
Banish Weeds from Walkways
Edging Garden Beds
Target Seeds to Stop Weeds
Spring Weed Alert
Pull, Prevent, Repeat Annually
Organic Weed Prevention

About Preen Weed Preventers

What's the difference between weed killers and Preen weed preventers?
How does Preen weed preventer work?
Is there an organic weed preventer?
How does Organic Preen garden weed preventer work?
Do Preen weed preventers build up in the soil?
Do I have to stay out of the garden after watering in Preen?
Can I use Preen by my water garden?
What does this mean: "Not for use on soils with more than 10% organic matter."

Preen in the Garden

What if my dog digs a big hole in the garden?
When do I apply a second round of garden weed preventer?
Does unusually rainy weather affect Preen?
Can I use Preen around shallowly-planted perennials and summer bulbs?
What if I've already applied Preen, can I still plant new plant material there?
Why does the Preen label indicate use with specific plants?
Where can I find how-to videos about weed prevention?

Southern Weed Prevention

How Does Southern Preen Work?
Name some problem weeds Preen Southern controls?
What other southern Preen products are available?
Can I use Preen Southern in the vegetable garden?



Weed-Stopping Strategies

Use Einstein's Approach: End the Insanity of Weeding (Back to Top)
To the full story
“Insanity,” said Albert Einstein, “is doing the same thing over and over again and expecting different results.” He probably wasn’t talking about weeding. In fact, his lakeside Berlin garden was famously weedy (he preferred sailing). But the great man’s thought does apply. If your approach to weeds is to simply roll up your sleeves each spring and yank them out then… well, see the quote above. Because there is a better way. Focus on preventing weed seeds from growing each spring and you’ll have a weed fighting strategy from which you can expect great results.

Hate Garden Weeds? Plant a Forsythia Bush (Back to Top)
To the full story
If you hate garden weeds, plant a forsythia bush this spring. Planting a forsythia bush now can reduce time weeding for years to come. The golden buds of forsythia are part of nature’s early warning system. They’re a natural backyard “weed alert” signaling that the seeds of crabgrass and other early weeds will begin to germinate in a few weeks. This means it’s time to get outdoors to do two things: apply mulch and sprinkle pre-emergent on top of it to stop garden weeds, as seeds, before they start growing.


Why do weeds overtake gardens so fast?(Back to Top)
Most plants we call weeds are uniquely programed by nature to survive and thrive. Most propagate by seed and the worst offenders can produce tens of thousands of seeds per plant, per season. Common lambsquarters, for instance, can easily produce up to 70,000 seeds annually per plant, seeds that can last decades if left undisturbed below the soil surface. Thus a yard already over-run with weeds is essentially a monstrously efficient weed seed producing machine!

Not all seeds sprout into weeds immediately, of course. Millions of them settle into the soil where they can wait years for a bit of sunlight to spark them into growth. That's why well-intentioned efforts to clear a weed-ridden bed often backfire by unleashing a torrent of new weed growth, as the very act of pulling up weeds and their roots unearths underlying seeds that quickly germinate at the surface. Particularly pernicious are broadleaf perennial weeds, such as knotweed, purslane and thistle that propagate by seed and also vegetatively, regrowing from bits of the plant or root. If you chop up these types of weeds, you merely make more of them. For more information on weeds and weed prevention, see www.preen.com.


Is it possible to ever "win the war" against weeds?(Back to Top)
Yes it is, but not without a battle plan that focuses on a combination of weed prevention and routine spot action. The good news is that, once you get ahead of weeds, it becomes easier and easier to stay ahead of them. The old garden adage hits the nail on the head: one year's seeds equals seven years' weeds. The weed war is truly all about seeds. Weed prevention hinges on: 1) stopping current weeds from going to seed and 2) preventing future weed seeds from sprouting. The trick is to make weed prevention a yearly routine that, if followed, becomes increasingly easy over time. For more information on weeds and weed prevention, see www.preen.com.

What's All the Fuss About Forsythia? (Back to Top)
To the full story
Yellow forsythia blooms are what botanists call a phenological symbol. When forsythia bushes bloom in a given area, one can be sure that certain other things are also happening simultaneously: the soil is warming, microbial activity is stirring and conditions are ripe to jolt certain seeds and buds into action.

Spot the 800-pound Gorilla in the Garden (Back to Top)
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Where is the 800-pound gorilla in the garden? Anywhere he wants to be. So goes a variation on the old joke, but in truth there is a pushy, bullying bunch of gorilla metaphors in most gardens. They’re called weeds. Left unchecked, they run rampant, leaving no recourse but a relentless cycle of digging and pulling.


How can I get the jump on weeds & minimize weeding all season?(Back to Top)
Ideally start your weed prevention efforts early in the season – but understand that any time is a good time to start as there's always a plentiful supply of weed seeds ready to sprout, given even the slightest opportunity.

First, remove any existing weeds, including the roots. Starting with this clean slate, add a layer of protective mulch to starve any just sprouted weeds of sunlight. Next, apply a pre-emergent weed preventer such as Preen to prevent any existing weed seeds in the top layer of soil or mulch from forming roots. No roots, no weeds, no weeding. Using a combination of mulch and weed preventer provides a double whammy of control.

Periodically, a few weeds will still crop up – remove them. Re-apply weed preventer mid-season (per product instructions) to keep seeds from the current year's weed crop from germinating, bearing in mind that many weeds set seed in late summer or fall. Refresh mulch as needed. Each spring, as you start the process again, you'll find fewer and fewer weeds to deal with. Following a simple seed-focused routine allows you to literally turn the corner on weeds.


Survey Figures Bring Gardeners To Their Knees (Back to Top)
To the full story
A spring 2011 survey found that gardeners spend more than 5 hours a month weeding. A pre-emergent weed prevention program can reclaim those lost hours.


Stay Six Steps Ahead of Weeds (Back to Top)
To the full story
This story offers tips on using mulch, weed preventer and a strategic approach to stay six steps ahead of weeds by stopping them as seeds.


Banish Weeds from Walkways (Back to Top)
To the full story
Gardeners hate weeds, period, but few weeds are more annoying than the ones that cram themselves into the cracks and gaps of stone, brick or gravel walkways. One smart way to minimize future weed growth in these areas is to use a pre-emergent such as Preen to stop weed seeds there from ever sprouting.


Edging Garden Beds (Back to Top)
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Professional landscapers know that digging sharply-defined edges around garden beds adds more than visual appeal to a property, edging also makes maintenance easier. Those crisp clean borders are trenches designed to stop grass and weed encroachment.


Target Seeds to Stop Weeds (Back to Top)
To the full story
Gardeners don’t need a “weed seed radar” to know that garden beds are swarming with hidden weeds – in the form of dormant seeds -- ready to burst into action with the arrival of seasonal weather or soil disruption. Even the tidiest of gardens harbors an army of weed seeds buried in the soil.


Forsythia Puts Gardeners on Spring Weed Alert (Back to Top)
To the full story
When spring weather warms the top layer of soil to 55° F weed scientists know that conditions are right for two things to happen: forsythia blooms and crabgrass seeds kick off the weed germination season.


Pull, Prevent, Repeat Annually (Back to Top)
To the full story
When it comes to repetitive chores like cooking, cleaning, mending and, yes, also garden weeding there’s always a “better way” to do things. With weeding, a better way combines maintenance and prevention. For gardeners it’s critical to eliminate existing weeds, while also preveningt future weeds.


Organic Weed Prevention (Back to Top)
To the full story
In spring, as vegetable gardeners gear up to sow homegrown produce, dormant weed seeds lie buried in the soil, ready to sprout the instant conditions are right. And sprout they will, leaving fledgling beans, zucchini, herbs and tomatoes to compete with fast-growing, naturally-adapted weeds for space, water and nutrients in the garden.


About Preen Weed Preventers


What's the difference between weed killers and Preen weed preventers?(Back to Top)
Preen weed preventer stops would-be weeds when they're seeds. By preventing weed seeds from forming roots, Preen helps keep a garden free of new waves of troublesome weeds. Weed killers kill existing weed plants and they work in various ways. Glyphosphate-based herbicides such as Roundup inhibit a plant enzyme that plants need to grow. Organic choices such as salt or acetic acid (vinegar) kill by dehydration. Pouring on boiling water or scalding with steam withers and kills the leaves and stems above ground. Of these methods only glyphosate kills the roots.


How does Preen weed preventer work?(Back to Top)
Weed preventers stop weed seeds from forming roots – so those weeds simply never happen. Preen Garden Weed Preventer's active ingredient, trifluralin, constitutes 1.47% of the product, with the rest consisting of the delivery medium, small granules made of corncobs and recycled paper. Once activated by water, trifluralin bonds with soil particles to create an invisible weed control barrier just below the soil surface. The barrier stops seeds from sprouting by inhibiting cell replication in the root hairs.

In the garden, Preen remains effective for up to three months for Preen Garden Weed Preventer and up to four months for Preen Southern Weed Preventer. Preen weed preventers do not persist in the soil, nor will they leach into groundwater. Preen's active ingredient breaks down and biodegrades and within six months to a year or so is no longer active. (Preen Southern Weed Preventer contains .27% dithiopyr as its active ingredient, which works in a similar manner).


Can I use Preen by my water garden?(Back to Top)
Preen garden weed preventers should not be used near aquatic ecosystems. It is important to never use Preen near ponds, streams, creeks, rivers or water gardens. Nor should it be used near or in water from swimming pools, drains or sewers that may find its way into an aquatic ecosystem. While the product will not wash out of soil, avoid areas where eroding soil might wash into bodies of water. The product should be swept from walks and driveways, and care should be taken when washing tools and discarding containers.


Is there an organic weed preventer? (Back to Top)
Corn gluten is an effective organic weed preventer. It contains amino acids that disrupt secondary root growth, thus preventing newly-germinated weed seeds from taking root. One 100% organic corn gluten option that prevents weeds for four weeks or more is Organic Preen Vegetable Garden Weed Preventer. Organic Preen uses corn gluten as its active ingredient. Its container comes with a fliptop applicator that makes it easy to distribute the corn gluten granules evenly in the garden. The good news for veggie gardeners is that corn gluten works best on soils that have been well amended with compost. Corn gluten is also a natural source of nitrogen, so if you use corn gluten you may need less of other types of nitrogen fertilizer.

Organic Preen can be used around established vegetables, fruits and herb plants. For obvious reasons, don't apply a seed inhibitor over newly seeded areas, wait until plants are two to three inches tall and have set true leaves. Organic Preen is also perfect for use right after transplanting or setting out pre-started plants. Sprinkle it on the soil surface, keeping it out of planting holes. Organic Preen can be reapplied every four to six weeks. It's completely organic and safe for use in vegetable gardens all season long, even to the day of harvest.


How does Organic Preen garden weed preventer work?(Back to Top)
Preen's organic product is made of 100% corn gluten, a by-product of corn processing. Researchers at Iowa State University discovered that corn gluten contains amino acids that stop seeds from forming roots, making it an effective organic pre-emergent weed preventer. It's especially suited to use in vegetable gardens. Organic Preen's easy-to-use container has a flip-top applicator designed to spread the pellitized corn gluten at the right rate of dispersal. Where seeds are planted, apply corn gluten weed preventer after seedlings develop true leaves and reach two to three inches in height. Reapply after four to six weeks.


Do Preen weed preventers build up in the soil?(Back to Top)
The active ingredients in Preen weed preventers do not persist in the soil. Once applied, they bond with soil particles where they do their work, then are consumed by soil microbes and biodegrade and within six months to a year or so are no longer active. Preen weed preventers are not water-soluble and will not leach into ground water.


Do I have to stay out of the garden after watering in Preen?(Back to Top)
After Preen granules are watered in, people and pets should stay off the area until the surface is dry to avoid tracking the wet granules on the lawn or elsewhere where they might stain porous surfaces. Once activated by water, the active ingredient in Preen is released from the granules to bond with soil particles in the top few inches of garden soil. There it creates an invisible weed control barrier. The little Preen granules still visible on the soil surface are made of corncobs and recycled paper and also break down in the soil.


What does this mean: "Not for use on soils with more than 10% organic matter." (Back to Top)
To most people, 10% organic matter probably sounds low for garden soil. Most people probably figure that their own garden soil has a significantly higher percentage of organic matter, especially if they amend their soil each year with compost to improve soil structure, nutrient-retention, aeration, drainage, etc. Yet, even with routine annual boosts of organic matter, most garden soil typically contains only 3% to 8% organic matter, with 5% to 6% being the norm. The information is relevant to those who might advocate such practices as growing plants in 100% compost, a practice not generally advised.


Preen in the Garden


What if my dog digs a big hole in the garden?(Back to Top)
If your dog (or you!) disturbs garden soil in a major way, it's time to think weed prevention. Turning over the soil exposes dormant weed seeds beneath the surface to the light they need to sprout. For big holes, re-fill with soil then apply a layer of mulch. For maximum weed prevention, add a sprinkling of Preen garden weed preventer granules. This product stops weed seeds in the soil and mulch from rooting, plus stops new seeds carried in by the wind, birds and animals. If your dog digs up an area that's already protected by mulch and Preen, what you do depends on the size of hole. Large holes require the procedure above. Small disruptions, such as footfalls, are not a problem. These will not disrupt the weed barrier in the top layer of soil where Preen's active ingredient bonds with soil particles. This barrier easily reforms around depressions and small gaps, but not broad gaping holes.


When do I apply a second round of garden weed preventer? (Back to Top)
Most people apply a first round of Preen garden weed preventer in spring to prevent early-sprouting weeds from taking root. In mid-season, as the effectiveness of the product begins to wear off, it's smart to re-apply Preen to stop various late-summer- and fall-germinating weed seeds from sprouting. In northern states, reapply Preen after three months. The new southern Preen formula lasts four months per application.


Does unusually rainy weather affect Preen?(Back to Top)
Excessively rainy weather, especially combined with warmer temperatures, can affect how long an application of Preen garden weed preventer lasts. Warm wet conditions speed up normal biodegradation via increased microbial activity in the soil. This causes the carbon-based active ingredients in Preen and Organic Preen to break down and disperse faster than usual. The durations listed on Preen packaging are based on averages. If your area experiences a lot of rain, especially if temperatures are higher than normal, then you need to reapply sooner rather than later.


Can I use Preen around shallowly-planted perennials and summer bulbs? (Back to Top)
Preen creates a weed-prevention barrier in the top layer of soil and mulch, so you might think this makes Preen problematic for use around shallowly-planted perennials and summer bulbs. In fact, among plants tested for use with Preen garden weed preventers are such shallowly-planted garden classics as asters, begonias, daylilies, ferns, hostas, rudbeckia (black-eyed susans) and periwinkle (vinca) – all of which are planted right below the soil surface.


What if I've already applied Preen, can I still plant new plant material there?(Back to Top)
It's fine to add new plants including bare root perennials, bulbs, small or large container plants, and trees or shrubs to beds where Preen has already been applied as long as you take care to keep soil with Preen granules out of new planting holes. The best technique is to dig the planting hole, position the plant and then refill the hole with fresh soil and compost. It's handy to have a bag or two of garden soil or compost on hand each season for this purpose.

Why does the Preen label indicate use with specific plants?(Back to Top)
Preen labels only recommend use around plants that have been formally tested under scientific conditions. For Preen, extensive product testing has cleared its use with a broad range of plants including more than 200 different types of flowers, perennials, roses, ornamental grasses, bulbs, ferns, groundcovers, shrubs and trees. Has every garden plant been tested? No, the range is simply too huge. If you wish to use Preen garden weed preventer around ornamental plants that are not specifically mentioned on the label, it's recommended to test its use with a sample plant or two and judge the effects. In all cases, when planting, keep the Preen granules out of planting holes.


Where can I find how-to videos about weed prevention? (Back to Top)
Preen offers short, online how-to videos with tips on preventing garden weeds. You'll learn about the basics of weed prevention routines, tips on how to use Preen weed preventers, preventing weeds in flower and vegetable gardens and how to use mulch as part of a strategic weed prevention strategy. To view the videos, visit the Preen Scenes YouTube channel at www.youtube.com/preenscenes. Or visit the new Garden Tips section of the Preen website, www.preen.com/gardentips


Southern Weed Prevention


How does Preen Southern work? (Back to Top)
A: Preen Southern Weed Preventer is a pre-emergent that is applied to block weeds from growing in the top layer of soil or in mulch. Preen Southern’s active ingredient, dithiopyr, constitutes .27% of the product, with the rest being the delivery medium, small granules made of corncobs and recycled paper. Once activated by watering-in, Preen bonds with soil particles and mulch to create an invisible weed control barrier. The barrier stops seeds from growing into weeds by inhibiting cell replication in the root hairs. Preen Southern remains effective for up to four months. It does not persist in the soil, and will not leach into groundwater. Preen’s active ingredient breaks down and biodegrades within six months to a year. The little corncob/paper granules also break down in the soil.


Name some problem weeds Preen Southern controls? (Back to Top)
Summer weeds (spring/summer germinators): spurge, crabgrass, common lespedeza, carpetweed, mustard, oxalis, goosegrass, foxtail, pigweed, prostrate knotweed, and more. Winter weeds (fall/winter germinators): hairy bittercress, annual bluegrass, Carolina geranium, catchweed bedstraw (cleavers, stickywilly), henbit, chickweed, marestail (horseweed), corn speedwell and more.


What other southern Preen products are available? (Back to Top)
There’s dual-action Preen Southern Weed Preventer Plus Plant Food which comes in a bottle with a shake-top applicator. Its weed preventer, chosen specifically for long southern growing seasons, gives up to four months of on-going weed protection. Its balanced 6-8-6 fertilizer boosts flowering and helps plants build strong roots for better heat and drought tolerance. There’s also Preen Mulch Plus – the only bagged mulch available that’s guaranteed to prevent weeds for up to 6 months. It comes with added Preen weed preventers already mixed in. Packaged regionally and sold at Lowe’s and independent garden centers, the southern product features, variously, shredded premium natural wood mixes of local sustainable cedar, fir, pine, cypress or shredded hardwood. Three non-fade colors are offered, tinted with carbon black or iron oxide: chestnut brown, midnight black and russet red. It’s effective against weeds when applied 2 inches deep, instead of the 3 inches recommended for regular mulch. This means that one bag can cover more than 12 square feet, about 30% more coverage per bag than other mulches.


Can I use Preen Southern in the vegetable garden? (Back to Top)
Preen Southern is not approved for use in vegetable gardens. It is for use in flower and landscape beds. Instead use Organic Preen Vegetable Garden Weed Preventer.