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I am getting wildly conflicting information on mulch. Some sources say that it starves plants, keeps rainfall from reaching the soil, grows mold, rots tree trunks, and feeds termites. Other sources say it's critical in a desert environment like mine (15f-105f, 7" of rain per year on average)--that it prevents weeds, keeps moisture in the soil, and prevents erosion.

In the past few years I've tried various wood mulch strategies for large expanses of bare soil: deep (6"+) and shallow (1-2") wood mulch and pine straw. So far I have not gotten great results:

  • The ground does not stay moist with any method. The mulch seems to soak up all the water and the ground is dry a day after rain.
  • My worst weeds (Bindweed and Silver Nightshade) are not impacted, even with with deep heavy wood mulch. Less competitive weeds like Tribulus Terrestris are prevented, though (thank goodness).
  • Termites like to eat the wood mulch, not so much the pine straw mulch.

However, in places where I water (like around trees), the mulch does break down and become great soil. But in places that receive only natural irrigation, it does not break down, and the weeds take over. Why do so many desert gardeners swear by heavy mulch? I don't get it. Why am I not getting their results?

  • Bindweed and silver nightshade will never be deterred by any mulch, no matter how deep, both form an extensive and fairly deep root system and are highly persistent and difficult to eradicate. – Bamboo Jul 15 '17 at 17:59
  • So, uh, how do I eradicate them? – iLikeDirt Jul 15 '17 at 20:05
  • It says here cabi.org/isc/datasheet/50516 that silver nightshade is next to impossible to eradicate without use of chemicals. As for bindweed, do you mean Calystegia sepium when you say bindweed? If you do, I've never yet found a way of eradicating it completely - control with chemicals, yes, eradication, no, but you might be using the name bindweed for another plant – Bamboo Jul 15 '17 at 20:28
  • I think it is Calystegia sepium. Looks the same. I don't care as much about this stuff, since it's not spiky or poisonous, unlike the silver nightshade. – iLikeDirt Jul 15 '17 at 21:09
  • Well that's a point I suppose, but bindweed is a real bind, a reason not to buy a house as far as I'm concerned, gets everywhere... maybe its not so bad in the desert though. I agree with the answer given, that organic mulch is worthwhile, although it should never be in contact with a tree or shrub's woody trunk - best applied when the soil is already moist though. Not sure I'd use woody mulch where you are, not too keen on bark here in the UK either, too much fungal growth with it here – Bamboo Jul 15 '17 at 21:39
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Mulch is always a good thing for your soil. Always. Bark chips and other organic mulches won't 'feed' your soil until they are decomposed. Meanwhile they do shade and cool your soil. They sort of pull the landscape together visually.

The reason you might have heard mulch 'starves' your plants (poor terminology) is most mulches are not decomposed and anything once alive and has died is in the process of decomposition. Decomposing organisms use nitrogen as an energy source. So whatever nitrogen is in the soil, the decomposers use it and the plants have to get by with what is left over. While the decomposers are doing their job, all the other soil organisms, if there is no food, go to sleep, go dormant, die. When the decomposers have decomposed some of that mulch, the soil organisms come out of dormancy, eggs hatch, reproduction is fueled. All the other soil organisms outside of the decomposer crews, need decomposed organic matter for energy.

Plants need these soil organisms symbiotically. They help plants to take up the chemicals plants need to make their own food. Plants can survive in a 'dead' soil but they won't be vigorous and healthy. Healthy plants are able to defend themselves from disease and insects. Healthy plants can compete with the weeds. Healthy plants shade the soil and add more organic matter back into the system.

Desert soil is very porous so usually drainage is not going to be a problem. Getting decomposed organic matter into your soil is the most important thing you can do to improve your soil. Heck, the one and only way to improve ANY soil is by the addition of decomposed organic matter. For your soil in the desert it is critical.

Waiting for your wood chips, bark chips to decompose might be all you can do. If I were you I would call my local water and sewer utility to see if they make mulch out of human poop and sawdust. I got spoiled working in Seattle where this was available. It was all I used. Shoot, if a client wanted bark mulch I told them to find someone else. The price was the same! And I never lost a client. I simply gave them references after the big spiel and education and they were sold. I also had a bucket in my rig full of this mulch to let them feel, see and smell. It sold itself.

I'd put this on a new client's beds and in one week (when we revisited) the entire landscape was vastly different. My crews were always blown away, the clients were sold.

The only drawback for this mulch is that it is a bit high in heavy metals. I won't use it in the vegetable garden. But if you ever look at tap water...the heavy metals are higher to include fluoride!

Check your area for the availability of this stuff. If you have access to this you HAVE to use it! Don't get the stuff in bags. I've found that THAT is not the same, hasn't been completely decomposed...P U! This stuff is us humans giving something back that is good...makes us humans look like we belong?

If you can find this please let me know. How large is your property? What are your 'goals'...do you have a vegetable garden? Lawn?

Oh I have to say one more thing. As far as weeds go, putting 2" down on top of raw soil, on top of mature weeds is the ONLY thing I do for weed control. Period. I am not at all worried about weeds. If I don't have this Gro-Co, which I don't here in Central Oregon, I just dump soil on top of weeds or pull them before they go to seed. I got really spoiled by this stuff! If you do have access to this 'product' you are so lucky!! Dump it on top of your soil and you smother weeds, shade your soil, reduce evaporation, feed your soil, improve your soil...and that is all you have do. Of course you will have to replace/add more every other year because this stuff is being mixed into your soil by those organisms who eat it. They mix this organic matter and aerate your soil for you. This human poop mulch does more for soil than...well, any thing else. Your plants will be thrilled. Forget about weed problems. Oh, if you find this product...they will also be able to blow it onto your beds, around your home, around your plants for you...cheap cheap cheap and they do such an incredible job! Dang, I miss this stuff. Wonder what they do with our poop if they don't make this mulch, ummm? I know and I am appalled.

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    Just a note - Not all desert soil is porous! Desert soil is often full of heavy clay or caliche, and you should know what type of soil you are dealing with before planting or adding any other amendments. – Debbie M. Jul 15 '17 at 19:40
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    FWIW my soil is the opposite of porous: it's heavy clay and caliche. – iLikeDirt Jul 15 '17 at 20:07
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    This is amazing...10 bucks a yard? I would simply spread it on your ground where you want this wildflower/grass planting. If your soil is dry and not too high of a percentage of clay, go ahead and til. I would then add a couple more inches and in the spring I would delineate the boundaries, rake like crazy so there is soil in the surface mix and then ROLL with a water filled roller, rake to fruff up the surface and correct any dips or hills then use a spreader to spread the seed. Use the back side of your leaf or soft rake, then roll again. You are now in business! Water shallowly until – stormy Jul 15 '17 at 23:01
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    ...you've got healthy germination and plants with at least 3 sets of leaves. Start watering more deeply and less often...I would also plant some woody shrubs, a few trees and perennials that will give you 4 seasons of beauty and interest. – stormy Jul 15 '17 at 23:03
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    What an enjoyable project! You can play with this for now and be able to do more with this area later. I can't believe you have access to this stuff!! Could you send a pic of their flyer or brochure? I am not embellishing at all; this human poo decomposed compost is INCREDIBLE! Everyone keeps looking for miracles...this is a real miracle! You are one lucky dog! Let's make use of this...really? 10 bucks a yard??? – stormy Jul 16 '17 at 21:58
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In any environment it depends firstly on what the mulch is made of, I would try to make one of many things- I use leaf mould primarily since it contains certain nutrients and it stops soil erosion where I am. Secondly it helps with bacterial and fungal balances within the soil layer beneath and thirdly helps with water retention and frost protection for plant roots. However I find if the soil is already dry putting a mulch on top will not make it wetter than it is already- sometimes its better to wet before mulching or wait for a significant rainfall before applying. also one can add water retaining granules to soil to help hold on to the moisture. I remember that a soil covered in a organic mulch can help hold onto water up to 20 times longer than an uncovered bare soil or in the case I read about was about turf culture against flower beds and vegetable growing. Covering any soil with even a natural mulch of stones can help or even a man made material like plastic will help too- however if weed species that are perennial in nature are there too- the mulch of any kind will not help- weedkiller is one solution or a good old session of deep weeding will help out in the first few weeks- mulches do suppress light and do stop some weed seeds from germinating- I would recommend that a good mulch would have to be at least the depth compared to the width of your hand at least- remember the layer will settle and need topping up from time to time and newly planted plants will still need watering ever few days if the temperatures and winds get up high for several weeks or even months until established. For any mulch to add nutrients to the soil it must be fairly well broken down- if not, then any bacteria present will take any available nitrogen and use it to break it down before releasing it back- if one grows any potted plant in a mulch of pure wood chippings then don't expect good results for the first year or so- to counter act this problem a feed must be added to any planting too- just about anything with a bit too much nitrogen in its ingredients will do the trick. however I would recommend asking about how your neighbours get away with it- you never know they might be cheating or simply been doing it for ages- with any improvements to the local soil where you live it might take several seasons of perseverance to get good results- I would experiment and try anything that you can think of- you've got nothing to loose by trying. As one added note in south America the natives use a method of slash and burn to clear large areas to make way for crops, scientists found that in sandy areas the charcoal left after a major burn would act like a sponge and actually hold on to nutrients for longer- perhaps this suggestion might give you results without having to break the bank doing so. Stormy below is right in many ways one would not use water retaining granules on their own nor any method for that fact used singly as a proof of concept, as for the charcoal method that's based on scientific evidence however that method might not be applicable as I don't know what kind of soil is being spoken about- it does look as if it would work on a sandy soil not a clay one, the nitrogen quote is a well known fact often mentioned in organic publications and was taught to me at college plus the example is one I personally had at home on a large scale and was for most part an example of a failed project that eventually went right at the end.

  • I don't think so...burning has long ago been shown to actually waste great organic matter. Ash does little to nothing for the soil. – stormy Jul 15 '17 at 22:23
  • And water retaining granules or sponges or gels are horrible! In my opinion anyway. We aren't at the point where we won't be able to water our plants, our garden without being fined or imprisoned! The decomposers do not release the nitrogen back to the soil...unless you know something I've not seen or known. Please let me know if this indeed happens. – stormy Jul 15 '17 at 22:29
  • And the main problem with mulch is whether or not it is decomposed. If it is not, your soil has to wait until that mulch has been decomposed. – stormy Jul 15 '17 at 22:35

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