The MGS Forum
Gardening in mediterranean climates => General Cultivation => Topic started by: ezeiza on September 03, 2011, 08:24:54 PM
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I have been reading all postings and nobody seems to mention this most important topic in dry summer gardening, mulching.
Why is it not more widely used I wonder?
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I agree - mulching is an important subject.
It has been mentioned here before:
- carob fruit (http://www.mgsforum.org/smf/index.php?topic=186.0 (http://www.mgsforum.org/smf/index.php?topic=186.0))
- and a passing mention (http://www.mgsforum.org/smf/index.php?topic=247.0 (http://www.mgsforum.org/smf/index.php?topic=247.0))
But there is much to discuss...
Reasons for using (or not) - weed control, ease of maintenance (maybe), cosmetics, design element, moisture control, control of reflected light, etc.
Material:
- Organic - wood chips, shredded prunings, pine needles, etc.
- Inorganic - gravel/pebbles (different colours, rock types, acid/basic reaction, particle size and shape), impermeable plastic (translucent and black types), permeable membrane (eg. 'Mypex'), old carpet, etc.
Irrigation issues - harder to know that supplied water is going where intended, including rain water. If mulch diverts winter rains from the soil, the water table can recede, leaving plants vulnerable the following summer(s). And diverted storm water can cause erosion problems elsewhere.
Rooting issues - mulching can encourage plants to root near the surface, making them less drought resistant and less secure in the wind.
Cultivation issues - can be much more difficult to transplant, know how healthy a plant is (harder to inspect the soil for root-chewing pests, eg.), apply fertilizer, etc.
Cosmetic issues - coloured gravels (please, no!), Japanese Zen garden (gravel raked into patterns, etc.), white gravel can cause too much glare in the sun but can also reflect light into dark corners.
Costs
Supply - where to obtain mulch (which may be an ongoing requirement, if the type of mulch is one that degrades)
[David: thanks for this addition (update 4sep11)]
Maintenance and longevity - some man-made mulching materials degrade in sunlight, gravels can clog with leaves and soil, organic materials decompose (and may harbour pathogens), how best to dispose of old mulch.
Methods of installation - ground preparation, irrigation below or above, piercing impermeable sheets or not, overlapping joins
...Those are just some of the issues that come to mind immediately.
Please suggest others...
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For a mediterranean type climate I was thinking of a clear shredded wood mulch applied in spring, not a permanent one.
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To mulch or not to mulch, that is the question............and what with.? In the Languedoc I would mulch with what ever organic matter I had that had well rotted down. The problem then is that the mulch is rapidly photodecomposed and you have to start again next season and rotted organic matter is hard to come by. I then turned to pine bark chips which worked very well and lasts for several seasons. It makes a very good medium to walk on and sets the garden off.
Thus SUPPLY (and cost) is an issue omitted by Mike. I remember a Californian member saying that they would go to the local municpality and buy a truck-load of worked-compost and layer it on------------I think she said to several inches thick which sounds wonderful. Our local council produces the stuff but it is not available to the amateur gardener, I expect it will be one day.
I think I prefer mineral mulches since they never breakdown and offer most of the advantages however gravel and stones all take some finding, collecting and spreading. In the garrigue there is generally a covering of small stones and gravel.
The hunt for peat compost alternatives goes on and there is a lot of research looking at mixtures of grape marc, tomato soup waste and cattle manure, maybe this is the future.
I received a note from an MGS member in South Africa which said that gardeners there were having problems growing certain Ericas, Proteas and Heliophilis in Fynbos soils due to the possible build up of soil diseases such as Phytopthora. Soil-borne diseases kill lavender, rosemary every year.
I think you have to pay you money and take your pick. There is no right or wrong, its what works for you. David
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I would be happy if I could get hold of any organic mulching material, but so far I have not been able to find anything at all where we are in Halkidiki (northern Greece). I don't mind if I have to apply new material every year, it would certainly improve the soil we have tremendously. I bought 3 m2 of the best soil I could find last month, but it seems to have very little organic material. Fortunately, I had some partly decomposed compost I could apply on top of the soil which i hope will be an improvement.
We have talked about buying a shredder in Greece as well, we have one in Norway which we use all the time, and we produce huge amounts of very good soil here, more than we can use ourselves, so we give away a lot to our (lazy) neighbours. What is your experience from the mediterranean climate?
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The MGS has a useful beginners' leaflet on the subject reproduced as a word file here.
I garden in Attica which is rather like Cyprus in terms of poor soil and summer drought; also I imagine in the non-availability of organic mulch commercially. On two occasions I got a lorry-load of cotton waste delivered which made a wonderful black mulch once it had rotted but it smelt awful in the meantime. A material with a lovely smell and appearance was cocoa waste but the supply was cut off. Of course any organic mulch need renewing every year which is really the point because the mulch is improving the soil at the same time as protecting it. Unfortunately if I can’t find an outside source I find it impossible to keep up mulching with material only from the garden. I shred all the prunings I make which isn’t diseased but from a mountain of stuff you get a few square metres of thickly laid mulch, so then you have to decide who deserves it. I try always to mulch new plantings, keeping the material away from the planting hole. Then I look for places where the previous mulch has disappeared. I think that protecting the soil from the sun and wind is more important than conserving moisture. After the first few weeks of the summer there isn’t any moisture left in the top soil anyway. I choose not to use inorganic mulch.
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That`s the problem , getting hold of O.M. I used everything from vegetable wastes, soft and hardwood prunings cut down to 5-10cm lengths,old flowers, grass clippings etc. The compost heap also received lots of rain run-off so it was always moist.
I also spread ammonium nitrate (?) on it to provide nutrients for bacterial breakdown and also to encourage worms. I have never brought in soil. I think you have to work with what you have, make local adaptations and be ruthless in what is successful and what is not.
Fleur why do you not use inorganic mulches? David
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I favour inorganic types of mulch (albeit based on limited personal experience).
Thanks very much for that Word doc, Fleur.
Some themes seem to be emerging:
- supply is a problem (available but costly gravel and/or geotextile; industrial or agricultural organic wastes such as cotton can have problems such as smell; insufficient volume of indigenous plant material for shreddings; etc.)
- need to experiment and see what works (which may vary from place to place within one garden)
- need to consider the soil ecosystem (naturally inorganic soils can be upset by the addition of organic material, leading to fungal diseases, and plants' increased susceptibility to them, eg.)
Dear departed Geoffrey Smith used to describe good compost as being 'good enough to smoke'. I liked that, and thoroughly agreed (in principle). I am trying to teach myself to accept that a good growing medium in the Med. is, for many native plants, something different. Here, I don't expect to find earthworms when I dig (nor to be accompanied by a robin with similar expectations, more's the pity). For gardeners from cool temperate climes, it takes some getting used to.
(For non-UK folks: Geoffrey was a well respected gardener on British TV.)
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While the use of gravel, grit, etc. in Norway or Scotland would be fine, it will cause an overheating problem in full sun in a warm climate.
Sewage sludge, or stable manure would be choices for quantity, granted it is difficult to find them. What about shredded leaves: they must be available in quantities.
A powerful shredder is the best possible investment. Shredded material will occupy a lot less space, decompose faster and the wind will not carry it away.
Since we can not dispose of the very large quantities of autumn leaves for the compost heaps, we just dig them in the ground in beds. By the book this would be wrong but in practice they decompose in a couple of months and the soil becomes very grainy and porous. No signs of any nutrient shortage although admittedly our soils are naturally rich.
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Has anyone used Gypsum? I have been reading its good for dealing with Phytopthera because it conditions clay soils. I am not really sure about using it regardng safety etc.
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I have been using aged donkey manure as a mulch, especially around all the greedy guts. i.e. roses and clematis.
However, I have found that it doesn't disappear. In fact, it looks just the same now, as it did fifteen to eighteen months ago when I first put it on!
Daisy :)
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Both horse and donkey manure have a large amount of fibrous material which will not decompose rapidly if the conditions are dry
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Pamela,
Re gypsum: Interesting point. There seems to be a lot of information/misinformation about. This sums it up somewhat - http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Gypsum.pdf (http://www.puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Gypsum.pdf).
Its use in helping control Phytopthora seems to be reliable information: I just wonder about dosages, in non-agricultural situations.
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I suffer the usual problems when it comes to composting (ie finding the correct balance between heat and moisture) and mulching, finding sources of sufficient quantities of OM without having to pay large amounts for it. So when I find plants that don't need to be cossetted and literally thrive in poor soil they're worth their weight in gold. My daughter and son-in-law built a house on a slope and part of the property has a 2 metre retaining wall. On top of this wall is a narrow planting strip that was backfilled with all the sub-soil and debris from the foundations etc. I did nothing to improve this 'soil' but planted into it such things as; Eriocephalus africanus, Euphorbia veneris, Chrysanthemoides incana, Eremophila maculata and Asteriscus maritimus. The photos show the results a few years later. All the plants have performed 100% better than the same plants in my flat field with the reasonably fertile soil. The only thing they have going for them is excellent drainage when it does rain!
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V. useful comments John - more notes made - thanks
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Thank you Mike for that very interesting site of Linda Chalker Scott. I thought the articles on the Myth of Xeriscaping and also Leaf Wilt extremely interesting.
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Yes, indeed, it is something that Olivier Filippi is saying since a long time : mediterranean plants don't like organic mulch, they can be killed because of an organic mulch. Just have a look on the garrigue : the plants are thriving on grit and rocks and stones.
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Thanks, Pamela, for prompting me to look at some of Linda's other articles - indeed, very interesting.
I include a direct link here, because there are a few other articles on mulching
http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/index.html (http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/index.html).
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There is some circumstantial evidence building-up which suggests mineral mulches may in fact be the best /safest type of mulch. The control of Pythium and Phytopthora will be aided by good drainage, such as you find in the garrigue. The soils of the Languedoc are alkaline therefore it is doubtful that gysum (calcium sulphate) will help with the control of damping-off diseases. Gypsum works on clay soils. I suspect the rest of the Mediterranean Basin has similar soils.
It would be good if someone (my namesake Bracey, for example) could comment with a Californian view. How about in Chile, Eduardo??
David
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Mike, the link you gave us was extremely interesting, and not only the part about mulching.
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I was thinking about mulches today. I'm clearing an area under elms for a dry shade garden and before planting it up I thought to put down a mulch of bracken, the reason being that there is loads of it down the lane, and because I can't plant it up just yet and want to suppress weeds in the meantime.
What do you experts think of bracken? Are there any contra indications? Advice please.
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People in the US West Coast should know about this and that the practice of mulching they have used for decades and decades is wrong.
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Hilary, Composted bracken is used as a mulch in the UK. (Bracken does contain a carcinogen, but that is broken down by composting).
But in mediterranean conditions and for plants adapted to dry summers and winter moisture I'd go along with the Olivier Filippi school of thought, preferring mineral mulches to organic ones.
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Only that in this forum lots of plants with the opposite cycle (that is, warm season growers) have been shown and recommended. A mulching that would conserve soil moisture will be a real improvement.
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The thermal cover for my swimming pool is disintegrating (getting old).
It is blue plastic bubble film, and each of the 'bubbles' is rather flat topped. As it disintegrates, the 'lid' of each bubble falls off.
I have been skimming these little bits of plastic from the pool for some while now, and tipping them out (plus leaves, lizards, etc.) onto a new area of the vegetable garden. ...Gradually building up a mulch of blue plastic squares :)
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What happens to your plastic mosaic when the wind gets up, Mike? ;)
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:)
Actually, I hate having foreign material in the soil - tiles, concrete, nails, plastic, etc., and especially glass. So when the cover has finished 'moulting', I shall clean up and remove the blue bits as best I can.
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In answer to David:
Twenty reasons why I don’t use gravel mulch (but use shredded clippings instead)
- It’s made of gravel, as are all my paths. Also the lower part of the house is stone as are all the walls in the entrance and west side of the house – stone overload.
- In Greece it’s white. I don’t need any more white reflecting light and heat off at me in summer.
- Storage. Gravel has to be delivered in bulk and sit until used somewhere that the lorry can reach i.e. a central point, or else wheel-barrowed into a corner. Organic mulching material and shreddings are easily stored in the corner.
- Weight. I need the help of a strong male (paid) to load and wheel barrows of gravel. Organic mulch I can manage myself.
- Cost. Home-made mulch raw material is free.
- Infertile soil. My mix of terra rosa and subsoil is desperately low on humus and improves noticeably after a couple of years of organic mulch.
- Stony soil. My soil is already up to 50% stone (see below).
- Planting. When you need to replace a plant in the gravel it’s a pain in the neck to stop the soil and gravel mixing and the gravel getting into the hole. With organic mulch you just scrape it aside and if some gets into the back-fill it doesn’t matter.
- Weeds. Once the surface of the soil has been lightened by organic mulch the weeds pull out much more easily.
- Seedlings. Because I shred all my deadhead clippings I get lots of interesting seedlings around the place.
- Stops the stems of natives from rotting. You must be kidding; nothing stays damp in my garden. Anyway I keep the mulch away from the stems.
- Temporary. Basically mulching by the gardener is only a temporary measure because once the plants spread out and cover the soil they carry on doing the job all my themselves.
- Shredding. The task of shredding is pleasantly repetitive and sweet smelling if the prunings come from herbs or aromatic trees. In summer it’s a job for the shade. At which you might say why not just sit in the shade with a drink and a Kindle, but I have to admit that I never sit in my garden.
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Thank you for most interesting informations! We actually had to put a permeable fabric and stone chippings over it, as we bought a house a year ago with a garden (350m2) with nothing else but a cypress hedge, some yuccas and ficus trees and a grama lawn with millions of dandelions, thistles etc. Almost all the gardens in our corner (rain fall under 300) have stone chippings (usually marble, limestone and some rosa coloured stone), they don't cost much (40 euros a ton) and organic mulch would probably turn into dust. After this was done, I was quite frustrated to find out, how uncomfortable it is to plant through the membrane. There seem to be also different opinions, whether the temperature of the soil under the stones gets warmer or cooler in the summer. It is obviously not possible to improve the soil except around the plants, but our clay would be too hard work for an absentee gardener anyhow. It is a pity, that the plants cannot self seed with this layer, but the weeds have obviously less chance. For me it is a compromise, I am waiting for my new trees and shrubs to make it look greener!
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After reading all the interesting comments on mulching, here are our experiences from 12 years of gardening on a plot of 2300 sq m on the Greek island of Paros.
Our soil was very poor and stony to start off with and organic mulches improved its structure considerably but we couldn't say if they reduced water demands as we never had enough to lay down the recommended 10-20 cm. We had no problems whatsoever with stem rotting - climate too dry and windy.
We have tried the following: vine waste, olive leaf, products of home shredding (we have a small shredder and the use of a larger one), municipality-produced shreddings, home-made compost, manure and gravel, and what we have found to be the pros and cons of each material are listed below:
Vine waste/olive leaf
Pros:vastly improved soil structure/fertility; suppress weeds
Cons: can never get enough; supply seems to have dwindled (too many takers?)
Home shreddings
Pros: good way of recycling garden waste; suppress weeds; improve soil
Cons: never enough; a lot of hard work with not much to show for it, barely enough to mulch 20 or so plants - and we have over 700!
Municipality shreddings
Pros: similar to home shreddings
Cons: too coarse/woody; contains all sorts of rubbish; not available currently
Composted weeds/kitchen waste
Pros: recycled waste, mild fertiliser
Cons:not usually broken down enough, weed seeds survive
Manure
Pros: good fertiliser
Cons: introduces weed seeds; expensive
Gravel
Pros: looks neat for a season or two
Cons: Soil is blown on top of it allowing weeds to germinate and pulling out the weeds brings more soil to the surface; heavy; expensive. Very much in agreement with Fleur's comments
We have this year for the first time experimented with straw. We put down 30 bales - fast (completed in a couple of days) and not too expensive for the area covered (which includes almost all our plants). It remains to be seen how it performs.
I have a couple of questions:
a. Would winter rain penetrate below a thickly-laid mulch?
b. What is the fire hazard of a lot of bone-dry organic material underneath plants?
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Those notes on your own practical experience are really helpful, Alice; thanks!
To answer your second question, a thick layer of bone-dry organic material will certainly increase the fire risk. Research on wildfires in the last few decades has shown that the more fuel there is, the more frequent the incidence of fires. (This explains an odd paradox: in regions where wildfires are part of the natural regrowth cycle, fires tend to occur every five years or so in the higher-rainfall more fertile areas, instead of only every 25 years or so in the drier and more parched areas - even though one would intuitively expect these more parched areas to be more at risk from fire.) Also, the more fuel there is, the more intense any fire will be.
On the first question, yes, there's no reason why winter rain shouldn't get through to the earth below the mulch.
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Thanks for the information, Alisdair. One learns something every day.
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Hi all, I have been re-reading this topic with interest - I actually thought I had replied before, but perhaps I held back, feeling shy after so much anti-organic mulch debate (we use mostly composted or shredded garden waste).
For what it is worth, my experience agrees broadly with Fleur's comments about gravel vs. organic mulches. We are fortunate here to have a large area and lots of vegetable mass to play with (some parts are irrigated and growing in the summer and we still have lawns, much though I would like to dispense with those). The more woody material gets shredded before going on the compost heap, while lighter weeds, hay and grass clippings going straight there. The material does not always have a chance to break down very thoroughly, partly because we don't water the heap as often as we should, but it gets there in the end, and even if it is semi-green when it goes on the soil it does not seem to do any harm.
One exception is oleander cuttings - I have heard it said that these can poison the soil, but I could not tell you that they have definitely had an effect on plants in the garden here, where they have always been mixed in with large quantities of other material. I would be interested to know others' views and experience of this, or other plants to avoid putting back into the ground.
When I can get it, I bung a good load of manure on – but this is in the exotic garden; we try not to alter the natural soil conditions in the native plant zones, tough though they may be for young establishing plants. It is worth reiterating I keep all mulches away from the collar of the plants, be they sub-tropics or mediterraneans; but as Fleur has mentioned, nothing really stays wet for long enough to pose a problem.
In terms of benefits, I would highlight improving soil texture, supressing weeds and making them easier to pull out in future, and moisture retention. We have somewhat varied soil, in places very compacted, others extremely sandy, others almost pure clay, and the mulch helps in all of these situations.
One perspective that goes slightly against the gravel/garrigue argument is that an organic mulch imitates nature - fallen leaves are caught at the twiggy base of a plant in the wild, whereupon they do all the good stuff an organic mulch should.
I have also used gravel around culinary herbs and the like, and of course it has its benefits too, especially in pots, where a free-draining surface is useful. The other application where I would really recommend gravel/mineral mulch over organic is cacti and succulents - I have seen these improve literally overnight with the addition of a couple of inches of free-draining top dressing.
Hope that helps and please keep adding your views, it really is interesting and useful to compare notes.
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Are we trying too hard with our mulches?? Various members have written to say that structure is improved as well as water retention, ferility and so forth. Surely the point is that mediterranean plants have evolved to grow in "thin", well drained soils, with a relatively high pH and here we go trying to make the enviroment "better" like Victorian gardeners. Why not grow lawns?
Just a thought.
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There's certainly a case for what you say, David.
But I do think broad opinions on 'mulch' as a whole are complicated by the fact that the word 'mulch' can be used for different purposes, and maybe a single mulch can be used for more than one purpose at a time (eg. weed suppression and aesthetics).
By analogy, if we just had the word 'fruit', it would be no surprise that there was no consensus on how to grow 'fruit'. Thankfully, we have recognized different fruit and given them different names. That helps a lot.
We can use phrases to differentiate mulches, eg. gravel mulch, humic mulch, plastic mulch. That's good because it is a flexible system in which the terms are easily understood. But humans like shortcuts, and sometimes such phrases are too much trouble! Perhaps new words could be coined: eg. grulch, humulch, plulch? No, OK. 'tis late and my thoughts are wandering!
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Very good point David re mulches and I suppose the reason many people use them to improve the soil and conditions is that they want to grow things that are not entirely happy in Mediterranean climates. People who are hooked on gardening are not content to grow only things that are well adapted and will survive whatever the conditions, survive being the operative word because at times the resulting garden will not be particularly attractive. ???
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I understand that many of the barren areas around the Mediterranean were once covered in forests and that human activity (deforestation, domestic animal grazing, fires etc) and the resulting erosion led to the current thin, poor soils, in other words what we now see is a degraded habitat. Organic mulching is just giving nature a helping hand, imitating something that would happen naturally but would take decades or even centuries of no human interference.
In our garden, since we started mulching, we are seeing a build-up of topsoil and a vastly increased number of soil insects and earthworms, which in turn are bringing in more hedgehogs, lizards and birds, in other words an explosion of life.
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I suppose a lot has to do with our gardening habits, the choice of plants and the general life situation. If one gardens in the English way with lots of different plants very near each other, organic mulching comes logically. If you are an absentee gardener as I am, mineral mulch with a geotextile underneath (stone chippings or gravel over it) with only drought-tolerant plants is the most low-maintenance. Looks neat and you have practically no weeds, there have been no fungal diseases or other pests so far. If one chooses a light colour for the mineral mulch, it reflects the sun and the soil does not get overly heated (that is my experience), the moisture retention is good. After getting used to this comfortable way of gardening I am mulching now in Basel with lava rock and it is fantastic - no slugs, less fungal problems, good moisture retention. It would be useful to exchange, which plants like/dislike organic/mineral mulch.
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Alice please read "The Nature of Med. Europe " by Grove and Rackham where they rebut the idea of desertification and erroded landscapes arguing that the Mediterranean is a natural landscape caused over time by climate changes.
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Almost everything I have planted in my garden in Greece has been drought-tolerant plants, but it has been an uphill fight ever since the beginning, the soil is poor, clayey and with lots of rocks; when it dries, it is so compact that digging is almost impossible. Clearly a bit of mulching and soil improvement under these circumstances can’t be wrong?
I have a Campsis I planted more than ten years ago (don’t know which species, it was not named properly), it has barely survived and is now almost one m tall! no flowers yet. I am certainly not trying to make an English garden (or a Norwegian one), but it would be nice to see something besides dried, brown weeds around the house. Fortunately, all the rain last winter help, it actually looks better this summer than before.
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I have the same kind of compacted soil in Costa Blanca. Olivier Filippi, Linda Chalker-Scott and others say, that one should not make soil amendments with organic matter in the plant hole, but one should take care of the drainage and to mulch well. Linda Chalker-Scott warns putting organic matter in the plant hole, because the roots will not fight their way through the original soil, but go around the plant hole, where the water will then sit. The plant hole might later sink down. She also says, that there should be only 5-10% of organic matter in the soil and that most gardens have much too many nutrients in the soil because of the constant soil amendment and of course too much fertilizing. Linda Chalker-Scott is very convincing in her arguments and contradicts many common gardening beliefs.
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Absolutely, Jorun, we're making gardens which by their very nature are unnatural! For instance, I want to grow my plants much more densely than they would chose to be on the local mountian, so of course I adjust the growing medium to take account of that by using mulch and mixing compost into the planting holes. My plants never grow too lushly - the humus added seems to disappear quite quickly, I assume because of the heat. However I have found that once the plants have grown to make a complete ground cover, the natural leaf drop takes over the job of mulching and I don't have to bother any more.
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I agree with you, Fleur, I have made the same observations, when the plants have finally reached the stage where they produce their own mulch, then they are fine, but it my take several years, so why not help them a little bit in the beginning?
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Also there’s this business of “10 cm” of mulch as a requirement which can get you despairing before you start. I’m afraid I believe it’s another case of one author writing it and all the others just copying in blind faith. Anyway that’s my excuse for ignoring the instruction and feeling very content with a good layer of 3 - 4 cm.
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I think a 10cm depth of mulch is required to make any significant difference to water needs at the height of summer. But, of course, any amount of mulch is good and its benefits are many besides reduced water requirements.
I also find it most satisfactory when plants produce their own mulch; but, as we are placing them suddenly in a relatively hostile environment, why indeed not give them a helping hand?
To take up Marilyn's point regarding possible poisoning of the soil by Nerium oleander cuttings, I have two questions:
1. Some plants (e.g. Eucalyptus, I believe) are supposed to exude certain chemicals which discourage the growth of other plants in their vicinity. Would mulch from such plants retard growth where applied?
2. Can plants take up poisons from mulch obtained from highly toxic plants, such as Nerium oleander? If so, would that make edible crops dangerous for consumption?