To me, the mulch is the weed suppressant. It took me a couple of years to fully rid my garden of weeds, mostly Himalayan blackberry(it was even growing inside the garage), morning glory & dandelions. I kept adding thick layers of mulch & the weeds became easier to spot & remove. When I see new sprouts (like now) I just turn them back into the mulch. I also add mulch twice a year but more thinly now.

Jane

When I first made the beds in this garden, I laid cardboard over the weedy grass, then covered that with trimmings from a tree I was cutting back to bring in more sun. Later that year, after the roses were planted, 6-8" of mulch went on top, and I continue adding organic matter via daily collections of used coffee grounds from Starbucks throughout the year. The only weeds that came up were freshly seeded, and pulled out easily. As I've continued planting in these beds, weeding has actually become easier -- as long as I stay on top of removing anything that starts popping up in Spring. The vast majority of mine are Ailanthus altissima seeds that blow in from the yards of neighbors who allow these weed trees to grow, and I pull them by the hundreds in early Spring. By the time the roses start blooming, I've gotten them all out.

:-)

~Christopher

I use cardboard. It doesn't last long though, only a few months, because of all the rain we get.

I also use thick cardboard underneath mulch. excellent weed blocker. But be warned, if the area is moist, eventually cardboard and mulch will rot enough that weeds will find their way. Plus wind, birds and trees will drop unwanted seeds so endless battle. IME, cardboard blocks for about two years but what comes back is weak and therefore more manageable to pull as they come up. In my case, 30 min of pulling is all it takes in an area where I used cardboard as weedblocker. I get from our recycling center or from WM. And I am not above using pre-emergent as I have a big garden.

nothing because things like cardboard & paper can hinder water & air movement into the soil The Myth of Paper-Based Sheet Mulch

@wirosarian, that link is the DUMBEST essay I've read in a long time. Leave a piece of cardboard outdoors overnight and you will have a limp piece. That means it is COMPLETELY permeable. Also OP is talking about putting underneath mulch so no aesthetic issues. Perhaps in a commercial planting environment does paper get compacted but so does any soil and any mulch with freq traffic. Boy that was dumb how that person earned a PhD is beyond me!

The so called "myth" series often do not include documentation so there is no easy way to determine what the various statements are based on.

One can use Google Scholar with the search words mulch and cardboard to see what has been published in the scientific literature (normally, since the early 70s). The first "hit" in my search gave:

http://www.academicjournals.org/journal/SRE/article-full-text-pdf/F0B17B124213

One of the hits is to a Ph.D. thesis which may be of interest to those considering the use of a living mulch.

http://mro.massey.ac.nz/handle/10179/4102

For me, the cardboard lasted long enough to smother and kill anything underneath, but was completely rotted away by the following Spring. If you have Spring bulbs planted -- as I do now -- don't put cardboard down now as it may not be rotted away by the time they start to emerge. The method I described is really best for establishing a new bed. Once things are already in there, you'll do better to spot-smother during the growing season by laying down cardboard or newspaper around the plants you want to keep after they emerge, then covering that with mulch or other organic matter. Since I collect used coffee grounds daily from Starbucks, I spot-smother with used filters and cover with grounds.

I haven't encountered any of the problems described in the essay shared by wirosarian. Since I have self-seeding annuals in there now, I no longer lay down cardboard. Any weeds that show up in the beds now are newly-seeded, and as the top layer is very loose, these are easily pulled as soon as I find them. The key is getting to them as early as possible, before they set deep roots that may leave pieces behind to generate new growth.

:-)

~Christopher

Newspaper definitely. If it's a larger area with not much growing, large sheets of cardboard are also very good. About 6 years ago I made the mistake of using weed cloth and I'm still ripping pieces of it out. The point is, you want something that will degrade and rot over time. If you use something like weed cloth, the mulch will eventually just break down into dirt after several seasons and you will still have weeds growing.

Preen, then cardboard or newspaper (6 - 8 sheets), then cedar bark mulch. Repeat as the mulch breaks down. No plastic or rubber sheeting, please.

Sara, if you get lots of rain, cardboard and newspaper are fine under mulch, but if you garden in the desert or almost desert, cardboard and paper are forever-ha! Nothing breaks down if it's as dry as it is here, and I've tried it. I just put mulch down directly on the soil. I also use compost as mulch and stuff called Soil Pep. Regular bark mulch is also forever here and just blows around in the wind. At least that's my experience--ick. Lots of people here use it, though. I don't know how they keep it in place. Diane

Which Preen formulation are you recommending? There are at least 2.

If you are talking about the corn gluten meal one, (http://www.preen.com/products/vegetable-gardens/organic-weed-preventer) I agree.

If you are talking about the 2,4-D plus other chemicals (http://businesscenter.lebsea.com/msds/2464112.PDF) please notice the precautions that the safety data sheet gives.

An older formulation contained trifluralin. If you still use that one, please look at:

http://www.sciencedirect.com/science/article/pii/S0048969713005949

My experience is the same as Diane's. I had to remove cardboard where I tried it under a tree and after some years it was still intact and totally dry. The bark mulch keep wandering around so now I use just leaves, spent blooms, the softer parts from pruning, butterfly bush and vitex bush trimmings which are soft, and even throw rotten fruits or vegetables, bananas etc. under the roses that are bushy where the ugly stuff isn't readily seen. It works as well as anything, doesn't cost anything and I don't need to throw much away when I'm cleaning up the garden. Recycling is very satisfying.

Thank you so much everyone.

I soaked cardboard and newspaper to put down in layers under cane straw. I have to say they dried out pretty quickly and became impermeable. Did help for a while with the weeds though! Now I just mulch with leaves and cane straw.

I'm using cardboard pretty successfully.It works best when I put it down during the autumn,once the soil is already wet,because now I'm seeing that it does take quite a while for rain to penetrate the dry cardboard that I put down during the drought of summer. Bark chips on top,of course. I noticed that during the heat and drought of summer that putting down the cardboard/chips mulch seemed to help the roses tremendously;even without my watering them,the mulched roses did vastly better than those without! I guess they appreciate just even having their roots shaded from the cruel sun and heat. The chips alone would be nice, but they are expensive -too much so for me to be able to pile them up really thickly. Besides, my land is just too uncultivated: too many tap-rooted, perennial weeds,too much bindweed. I don't want to use herbicide, period. The cardboard does break down pretty quickly once it starts raining,and then it adds organic matter to the soil,so that's a plus.I am seeing now that I will have to re-do the areas that I did early in Spring, because weeds are startin to grow through the chips now that the cardboard has rotted away (the rotten pesky badgers did their share of tearing it up, too...) Earthworms seem to love the interface between soil and cardboard, too. So all and all, I'd say I'm all for it! Landscape fabric is the WORST. I pull it out only to find that the soil below, though free of weeds, is compacted and lifeless. The roses hate it; I don't think it's at all true that it lets moisture and nutrients pass through...

For large areas I just add organic mulch directly to soil. If it is thick enough it will suppress weeds. I am in hot and dry area and I agree with Diane's comment on paper never breakdown. For small areas between pavings I use a permanent inorganic mulch by making bags out of shade cloth and fill them with pebbles. These bags of pebbles just lie on the soil and never break down. They can be moved easily and if you wanted to add organic matter to the soil below yearly you could. All my roses in the paved areas are mulched this way and I don't need to spend much time weeding at all! This inorganic mulch also has excellent ability to keep the soil below moist but keep the humidity above low so win-win! The roots are happy and the leaves are happy.

If you look at my threads with rose bush pictures you'll find examples of this 'black mulch'.

To answer Henry, the Organic Preen.

Where do you get Organic Preen? Or is it just corn gluten meal? Like Seil, I have tried landscape fabric and other bases for mulch and they are a mess. I like the idea of the mulch breaking down into the soil, so I don't use anything underneath. The only time I use a barrier is for a path or around my AC units where I put pebbles down. The landscape fabric keeps the pebbles from getting embedded into the soil. But after a few years, weeds to pop up.

I find if you put enough mulch down and keep enough on there to cover the soil, it will stop most weeds. You will still get weeds now and then, but not as much if you have no mulch or not enough mulch. Most people don't put enough mulch down or let it get too thin before replenishing.

The locally-owned garden centers here carry the organic version of Preen.

I've appreciated very much the suggestions on here, this has been helpful, thanks.

Why can't you use fabric weed cloth? Is it not permeable enough?

I tried the fabric weed cloth in total exasperation one year. Nutsedge was and is a major irritant and a huge battle to keep it under control. A few years ago I listened to the misguided advice from a neighbor. I removed the present layer of mulch, put down weed cloth and covered it with another 6" of mulch. Boy I was proud of myself. Hours and hours of work would pay off and I wouldn't be dealing with that darn weed anymore.

That was the biggest disaster. The "nuts" the nutsedge weed grew from were still 6" down in the dirt that I laid everything on top of. Not only did those little "nuts" continue to grow they sent their sharp little green leaves up through the dirt, up through the weed cloth and up through the mulch and waved their pretty little green leaves in the middle of all my flowers.

They were now impossible to pull because of everything I had on top of the dirt. The next year I ended up paying a couple of teenage boys to take off all the mulch and take up the weed cloth. I didn't plant anything that year and attacked with nutsedge control. Eventually I replaced all the mulch and dealt with a few weeds coming up through the mulch. When I found one I dug down 4-6" and dug up the "nut".

Add me to the list of people completely disillusioned with weed cloth. My rose bed in the back replaces part of the lawn, and the weed cloth does zilch. The grass just grows right through it! We have the kind of grass that grows on stolons (runners) and weed cloth is wholly ineffective in stopping it.

Next year - cardboard.

In May 2015, I thoroughly weeded my 400-sq.-ft. rose garden. I did NOT lay newspapers, cardboard nor weed cloth on top of the soil; I just spread a 4-inch-thick layer of bark chips on top of the soil. Water, air and fertilizer percolate through the bark chips into the soil. Since then, not one weed has emerged!

Really thick layer of mulch is the best weed blocker. I also like bark chips. I only use pine straw on hills.