What weed covering should I use under my mulch?

Question

I am about to lay down new mulch in a flower bed for a customer, where weeds are highly prone to growing. I will also be weeding this flower bed throughout the year. My question is, what type of weed covering should I use? I have used fabric coverings before but the weeds broke right though.

Would I kill my flowers if I laid down plastic under the mulch and around the flowers?

Answer 1

You cannot use plastic - it will waterlog after rain. Weed fabric allows water and air through, whereas plastic does not. You can buy heavier duty weed fabric, so you might consider that, but most weeds do not punch through the fabric from the soil beneath, only things like japanese knotweed or bamboo usually. However, weeds can and do root into the mulch on top and their roots may penetrate the weed fabric over time - things like couch grass, for instance.

You also say you will be weeding the flowerbed throughout the year - that will be difficult with a membrane in place, so you might consider regular weeding, with no membrane but just a mulch in place instead.

Answer 2

I agree with Bamboo. That fabric makes a huge disconnect for the life in the soil and food, and air, and drainage. The 'food' in this case is decomposed organic matter that the micro and macro organisms of the soil need for energy. Plants need those organisms for vitality and uptake of chemicals (nutrients) for the process of photosynthesis with which plants make their own food and energy to grow. The cycle of plants and soil and organisms are horribly stopped. Plants will grow but they won't be vigorous and will be more susceptible to disease and insect damage. The plastic also is conducive for insects that don't live in the soil by giving them a habitat.

Weeds will grow no matter what. Any weed seed that is already in the soil will be stopped from germinating beneath 2" of mulch. The fabric is redundant for that purpose. Weed seed will blow in or get pooped out by birds in the mulch and will germinate and grow in mulch no matter what you do. Not very well however and they are easy peasy to pull up.

This plastic 'weed fabric' is possibly the top worst thing anyone could do to their plants and landscape. It was never meant to be 'weed fabric' in the first place. Some idiot marketer thought that up as a way to enlarge their profits. It was originally designed for a barrier between soil and gravel. If there is no fabric beneath gravel the process of walking or driving on gravel causes, 'sumping' at least that is what we called it in landscape construction and road building. When pressure is applied to the gravel. that causes the soil or 'fines' to rise to the surface filling the larger pore spaces of the gravel essentially causing the larger rock to sink below the surface and one has to replace their gravel periodically. With this fabric, the gravel will never have to be replaced.

Working in commercial and residential landscape maintenance, I made it clear that to become my client they had to pay me to rip that plastic up completely first. They had to pay big bucks to have my guys come in and remove every bit of that stuff. Weeds were usually everywhere and I also talked them into a different brand of mulch as well. Hey, I had a reputation and no way would I have a landscape with that plastic involved in my care. And not once did I lose a customer because of the extra cost. I was able to draw pictures of the mini ecosystem and they already knew that that stuff did not stop weeds. It was a no brainer.

I replaced their non decomposed bark with this product that was available in the Seattle/Bellevue area. I had no idea that this stuff is hard to find. It was called Gro-Co. A little tougher to sell but I always had samples to show and references always sold my new clients on this stuff. It is human poop mixed with sawdust and completely decomposed through a federally mandated process, tested 5X before sold to the public. The same price as bark. But people were able to know exactly what was in that decomposed mulch. Came with a document of the test on that particular batch of mulch.

Smelled wonderful, I am not kidding! Fine and uniform texture. Dark taupe color. NO pesticide residues that you get from other composts. NO weed seeds that come with all composts and bark mulches. High in Nitrogen. Absolutely gorgeous mulch. You could even have it 'blown' onto your beds and they did such a professional job! I tried holding onto the end of the hose (8" diameter) but wasn't ready for the power that took me straight up into the air! Nothing got onto the siding or foundation of the house, the little plants and grasses under pots...beautiful.

This mulch was all I would use. I hate bark or non decomposed mulch. I have since moved from Washington and have not been able to find another source in this state close enough to be able to use. Very sad.

This completely decomposed mulch is instantly usable by the micro and macro soil organisms. They don't have to wait for the decomposers to decompose bark chips, bark dust, bark chunks. Gro-Co fed the soil instantly. In one week, when my guys would visit for maintenance, they would be blown away at the difference in the plants themselves. They never stopped being so entranced at the difference in one week. Even fertilizing never produced what that mulch did. Yes, there is some Nitrogen but it was mostly because the soil came alive and plants were able to better uptake the chemicals that were already in the soil. The life in the soil is vastly important to plants. I never thought it would be so difficult to find, I mean, there is a lot of human poop to be had and sawdust. The hard part to sell was the idea that that mulch was once flushed down a toilet. I could do it just fine and got to know the owner of 'Sawdust Supply'. We talked a few times of course and he told me that they only did a portion of the poop supply in that area. The rest of the 'supply' was trucked to the center of Washington and pumped below ground 15 or 20 feet. I didn't tell him that that poop pumped that far beneath the ground did nothing for the crops above it but I am to this day horrified what it was doing to our subsurface fresh water. And this was just Seattle. I've made a few calls and yes indeed, those companies that take care of our sewage do the same thing; pump it below ground. I guess they are not allowed to dump it in our oceans and that is a good thing...

If I were you, where ever you live, I would call your city/county water and sewage department to see if this mulch product is available. If it is please let me know, okay? For us humans to actually be able to give something back that is a great environmental mitigator for our presence is rare! Bark, ugh, is causing our urban and suburban regions to become deserts! No food for birds, plants, soil...

Oh, one caveat. This mulch is a bit higher in heavy metals, so should not use it on vegetable gardens. I've seen, however, tap water test printouts that are higher in heavy metals than this stuff.

One more caveat but this one never caused a blink of an eye by my clients. This will need to be replaced every other year. My clients actually insisted on once per year. It disappears into the soil because the micro and macro organisms in that soil are coming up to eat this stuff, then going back down into the soil to poop it out. They actually and constantly improve the soil's tilth by mixing this organic matter into the soil without any labor on our part. The only way to make any soil a great soil is by adding decomposed organic matter into the soil. Adding sand, gravel, gypsum, lime, a little clay and water and rotate? You get concrete.

I hope this convinces you to not use landscape fabric except for when you install gravel. Horrid stuff. Pulling that out of landscapes was not easy nor pretty. Very expensive for the clients and they knew they never got what they thought it was supposed to do. Weeds were prolific. A few clients wrote letters, emailed their displeasure about being 'tricked' by these landscape fabric producers that called this stuff 'weed fabric'...never heard if they got compensation. Their compensation was having a landscape they could be proud. And they were all very happy! Weeds have been the least of my worries anyway even without access to this stuff. Weeds have gotten such a scary rap. And I for one have never had a problem with weeds. Now, when beginning a new landscape, yup, there is always the weed problem but hey, I had my wonderful crews to do that work.

And if this mulch is not available to you, the only other mulch I would use is the finest ground bark you can purchase. I would add nitrogen just to the bark to help the decomposers with their job. While the decomposers do their work all other life in the soil goes dormant or dies until that material is decomposed. Until that material is decomposed the soil life remains dormant. Adding nitrogen to the mulch will increase the rate of decomposition. You must figure this nitrogen into your fertilizer plan as you do not want to over fertilize nor upset the balance as higher nitrogen in relation to phosphorous and potassium will promote vegetative growth and you won't get many flowers on your showy flowering shrubs, perennials and definitely any annuals. One great source of nitrogen for your bark would be this kitty litter made of alfalfa pellets. Sorry for such a long answer but this is obviously a huge subject of mine. I am on sort of a mission to get rid of bark mulches that are making our cities into deserts, literally, and to encourage our sewage be used for a very positive reason rather than being pumped down into our fresh water sources.