Down here in the dreadful dry desert, we gardeners take mulch seriously (either that, or we have scary water bills). Mulch is useful in a variety of ways, including for those of you gardening in the damp. This diary will focus on using mulch in the desert, though I will try to present as comprehensive view of mulching options as possible.
As always, I welcome all comments, tips, etc., from which I learn at least as much as I teach.
So, why mulch? I find questions beginning with "why" to be less than manageable; so how about a few variants - "What does mulch do?" or "What sorts of problems can mulch cause?" or "What sorts of mulch are the best?" Stuff like that.
Or even better yet; "What is mulch?"
Mulch can be a lot of things. It can be a barrier, a habitat, a pile or a layer. My American Heritage defines it as "A protective covering, usually of organic matter such as leaves, straw, or peat, placed around plants to prevent the evaporation of moisture, the freezing of roots, and the growth of weeds."
Not too shabby a definition, though I'm surprised at peat being in there. I've never heard of anyone mulching with peat, though it is used by some as a soil amendment.
We do not expect our dictionaries to provide us with information beyond what things are, so I will not castigate the compilers and writers of the AH for not including everything that mulch does, especially mulch made up of organic matter, which technically means stuff with carbon in it; i.e. stuff that was alive at some point and has not decomposed to the point where it no longer has carbon in it.
The examples of mulch above all have a lot of carbon in them, and they will all decompose when exposed to nitrogen. Nitrogen is an important plant food as well, so if you are short on available nitrogen in your soil, your mulch can actually rob your plants of food. Unadulterated desert soils tend towards this problem, what with nitrogen being limiting.
Not all mulch is organic. Some examples of non-organic mulch include rock, brick, concrete, and plastic.
People generally don't think of rock or concrete as mulch, but they surely meet the AH criteria above. I don't go out of my way to use concrete, but if you're planting near concrete, there will be more water available, as it collects under the concrete barrier. You can see this around sidewalks, when the weeds grow bigger closer to the walk.
But flat pieces of concrete make a good mulch, and indeed commercial stepping stones are often just that. Some people make walkways with them, or with brick, and you can use the moisture retaining qualities of these faux stones (and real stones as well) to your advantage, by planting low-growing herbs or small flowers next to them.
Another thing the American Heritage doesn't mention about mulch is its use as a barrier to critters that might dig up your plants, such as your dog or cat. Brick, stone and concrete are excellent for this; the latter if you have broken pieces handy. I've found the flatter, larger pieces of these hard substances easiest to work with, and I don't usually use brick as a dog-digging barrier. But when planting an isolated plant, especially a larger one, laying flat pieces of rock or stone around the base can work well to discourage your pet's activities. I was told recently by another Kossack that chicken wire laid flat will serve the same purpose,because animals don't like to entangle themselves in this nasty foreign substance, and that you can even do this to keep deer away, when you raise it up some! So, mulch can be aerial as well. Who knew?
Some people use gravel or other small stones as a mulch. This can look nice, but it won't necessarily keep out weeds, and can compact with blowing dust and become difficult to weed. Even putting down plastic as a substrate beneath the stones will not keep this from happening, and may even make the situation worse, as the soil filling in between the gravel pieces cannot interact with the substrate and its attendant moisture, and can become concrete-like in desert areas, but still support some weeds. The thicker the layer of gravel/dust, the worse it will get, and the thinner the layer, the faster the plastic will get holes in it, where weeds will also grow.
But I'm an organic gardener, and thus not a big fan of plastic, so I will admit some bias here. Another, more recently engendered example of garden plastic, plastic mulch chips; I just plain don't like. They strike me as an example of the downsides of recycling plastic; that corporations use this free returned plastic to manufacture things out of plastic that we either don't really need, or that have better, non-plastic alternatives.
I use plastic things in my garden sometimes, but a good organic mulch should feed the soil, which plastic will not, other than to lend increasingly small bits of plastic to it, which may even absorb equally long-living synthetic toxins, should any be present.
Even rocks will slowly add nutrients, but plastic, while technically organic (ask any chemist!) will not do anything good for the composition of your soil.
So, let's get back to organic matter. What sorts of (non-plastic) organic matter can you mulch with? Lots of stuff. Here's a list, and I'm sure I'll forget quite a few items:
Straw, hay, bark chips, ground bark, shredded bark, tree limbs, produce scraps, pulled weeds, eggshells, nutshells, hair, green leaves and twigs, dead leaves, rough compost, finished compost, commercial compost (mushroom compost), composted manure, commercial "manure, (that isn't)" newspaper, cardboard, other paper, peat moss I guess, coffee grounds, kitchen scraps, cacoa bean hulls.
I'll finish here with some thoughts on selected items, in no particular order:
Back before I lived where one could easily obtain hay or straw, I used to think straw was better than hay, because it wouldn't have seeds. Where I live, the oat straw has seeds, though the oat grass is easy to pull up and makes good mulch too. The hay tends to be alfalfa and doesn't have seeds, and also it's a bit green which is good for feeding our desert soils. This was a good lesson in not trusting one's preconceptions.
My favorite mulch is bark chips, which I expect are a byproduct of things like toilet paper manufacture. It's hard to imagine how the people who owned this bark make much money when it retails for a few dollars a sack, but I'm glad that they don't pay to have it hauled off to landfills, and instead keep truckers employed hauling it around so that I can use it in my garden.
I like bark because it holds moisture, insulates, looks nice, decays gradually into the soil and adds humus, and comes in different grades, so you can use shredded bark or finely chipped bark as a soil amendment, or large chipped bark as a mulch that you can gather and re-use.
Large bark chips include little pieces of tree limbs, and tree limbs are handy for placing decoratively here and there, and they will serve the same purpose, albeit more slowly.
I'm still not sure about peat moss. European peat is a marginalized habitat and gardeners there should not use peat, as far as I understand it. Canadian peat? Well, the Canadian Peat Moss Association thinks it's okay. It's a larger habitat and has been hit by humans only relatively recently. But as long as we're growing all these conifers for paper and people are almost giving away the bark, I'd rather use that. Peat takes a very long time to become peat.
I use produce scraps in compost mainly, but sometimes I mulch with them. It depends on what they look like and what they do. I've gotten to the point where I don't even really have a category in my mind anymore called "produce scraps." Too general.
Pulled weeds work as mulch just fine; but it's best if they don't make more weeds to pull. I don't mulch with seedy weeds, especially from invasive species, or with spiny weeds (I like to walk barefoot), or with Bermuda grass runners. All that stuff goes in a pile in the back until it's dried out and thoroughly dead, and then I compost it just to make sure.
Mushroom compost looks like something that ought to be wonderful, doesn't it? I think mushroom compost's success is one of the great advertising hype successes of the modern world. This is spent mushroom cultivating potting soil that may well have sterilizing agents in it, as your average mushroom grower likely wants to make sure he or she is growing the right sort of mushrooms.
Manure in bags: make sure it's really all manure. Lately some companies have taken to selling wood products with some manure mixed in, and putting "Manure" on the bag in big letters, when it's only maybe 30% manure.
Cacoa bean hulls: These may be really good for feeding the soil, but they are also apparently really good for poisoning your dog, even more so than strong chocolate. Caveat emptor.
Coffee grounds work; they are fairly acid (low 5's in pH) so keep that in mind. I'm told that coffee shops may be willing to give them to you for free.
Mulching with compost is an interesting idea. Mulching instead of composting is an interesting idea too, especially if you have a limited amount of organic material to work with, or space limitations.
I resemble both of those remarks, so lately when I have something that's grown in my yard that I feel the need to cut back or pull up, what I think first is "Can I mulch with this?" I've found this inspiring and as a result my yard is a bit tidier, and my vegetables a bit more mulched. Instead of thinking; "I must trim, I must weed, I must do my chores, yawn;" I'm thinking "Where's there some mulch I can harvest?" Really, it's all I can do to restrain myself from over-trimming the shrubbery.
I don't mulch with paper or cardboard, though some do. I read something on a link another Kossack gave me on an earlier gardening diary that I posted here, about how cardboard has nasty glues in it; I'm not sure I'm willing to buy into this without more detail. We're not allowed to use lead ink anymore, and I used to correspond with a guy (Jim McNally was his name, as I recall) back in early Internet days, and Jim was this industrial composter who posted his butt off and was really educational on the subject. He told us all over there on Prodigy (remember Prodigy? Ick.) that there is much one can compost, if one has the space and the materials, but that what you have to watch out for is heavy metals. Jim also told us that he was at least partially convinced that paper (including cardboard) should be composted, not recycled; that this was more environmentally sustainable.
That's all I have to say on mulch at the moment; I'm busy now working shade/insect barrier devices for the tomatoes, which involve shadecloth, tulle, and paperclips, which are really handy for attaching fabric pieces to each other. I'm hanging them off the rafters etc. with nylon cord and wire. I have to work on shade and mulch both now, as the city is talking about starting water rationing, surprise surprise!
If I do manage to grow a tremendous amount of vegetables with my newly improved and greatly extended garden (several hundred square feet!) I'm planning on talking to the local food bank and community kitchen about donating extras to them. And then, if it gets really bad, and they try to keep me from watering my vegetables...I'm going after the people with big lawns.
It's a tough job, but somebody has to do it.