Advice on shredders / old grass clipping thread
- To: Medit-plants
- Subject: Advice on shredders / old grass clipping thread
- From: i*@cgac.es
- Date: Tue, 12 Oct 1999 10:18:14 +0100
Nancy, a grass clipping thread came up a few months back. I found the
debate so interesting that I kept a lot of the messages. I have attached
as many as I could find. Enjoy!
Damian
> Does this mean I should put my neighbor's grass clippings down right away,
> and not wait until it dries out and turns brown?
>
> Nancy
> Los Altos, CA
> USDA zone 9
> Sunset zone 16
********************************************************************
Damian asked:
> Can anyone comment on the relative benefits of raw grass clippings as
> mulch? I have recently started experimenting with it rather
> enthusiastically, mainly to give protection from heat and fierce sun to
> my last round of native plantings in our wildlife garden (wild olives,
> tamariscs, carob trees, figs, arbutus, wild almonds). Another benefit is
> water retention for our rather poor sandy soil. The attraction of grass
> clippings to us is availability (unlimited) and cost (zero): Many of my
> neighbours with ample green lawns thoughtfully leave great black bags of
> the stuff outside their gates after the week end. It doesn't seem to
> have quite as big a "sponge" effect with water as leaf mulch and it
> does tend to matt if it dries too quickly after a soaking. This last
> effect concerns me as I have recently lost some newly planted Celtis
> australis and I haven't ruled out "pressure cooking" of the roots due to
> an unwise combination of grass mulch, water and excessive heat. But, as
> I say... its free!
>
> Damian Martin
> Talavera, Central Spain (hot dry Summers, cold Winters)
Barry Garcia said:
> The only problem i could forsee is if you use it fresh (meaning right from
> the lawn) it tends to clump. It probably wouldnt hurt if it were dried out
> first (and this makes it lighter and easier to spread too).
>
> Anyway i know that large garbage bags of mulch (old christmas trees) are
> sold for just 75 cents a bag around here. The best thing about it is it
> keeps the soil consistently moist and my Viburnum can go for nearly a weed
> without wilting due to the mulch (it was transplanted from my grandmothers
> yard).
Susan George said:
> Damian
>
> I have used raw grass clippings (but not any more) - the main problem I
> experienced was grass and other weed seed germination in my garden beds -
> but certainly better than no organic matter at all (especially on sandy
> soil) - another problem might be the so called 'nitrogen draw down' effect
> (basically as raw materials rot/compost they use up nitrogen in the process)
> but if this is a concern additional nitrogen can be added. Personally I now
> put all my grass clippings in the compost bins and given a few months with
> other ingredients they are great (if you can get it to the right temp you
> can even cook the seeds) - no problems! - but you have to have the space,
> time and energy to invest.
>
> Susan George
> McCrae, Victoria, Australia
>
Richard said
I scatter green lawn clipping lightly around my vegetable plants to help
shade the soil and conserve water. Once a planting is harvested, the
clippings that remain on the surface are turned into the soil.
I maintain a 2-4 inch permanent mulch of chipped tree trimmings
elsewhere in
the yard, at the base of shrubs, carpeting my orchard and lining the
paths of
the vegetable garden. When I have too much green grass clippings, I
scatter
the excess lightly on top of the wood mulch and it disappears. I think
it
helps the wood mulch to break down without causing nitrogen deficiencies
for
the surrounding plants.
Richard
Northern California, Sunset zone 17
Dave Poole said:
> If the soil is already moist before spreading the clipping, they act
> as excellent moisture retainers, however their use is not without
> problems. If they piled too thickly and 'pan down' becoming too
> compacted, they will heat up rapidly as a result of anaerobic
> bacteria, creating a slimy mass which further needs to take valuable
> bacteria from the soil in order to break it down to a nutritious
> mulch. Effectively they de-nitrify the soil temporarily and can in
> extreme cases, cause temporary deficiencies in growing plants at a
> critical time in their growth cycle. Ideally the clippings should be
> dried before spreading and only spread to a depth of around 2 inches
> maximum.
Schmiege said:
> In my Greek climate of hot, dry summers without rain, I use grass clippings
> in my vegetable garden . I line the rows with rows of brown paper bags and
> on the top I put put thick grass clippings. After it is dry I move the
> grass closer to the plants. All the water is done with dripper lines so the
> grass does not get wet until the winter rains come and the whole thing is
> worked into the garden. I think the soil has improved since I have been
> doing this and it sure beats hoeing and weeding, plus the number of hours of
> watering the plants has been cut in half.
Jerry Heverly said:
> Let me introduce another concept, one that many of you may be familiar
> with; allelopathy.
> Everyone knows that the leaves of *Juglans* species contain toxins
> injurious to other plants. It's a readily understandable genetic advantage
> for one plant to be able to suppress the growth of potential competitors
> for scarce nutrients. A researcher at the University of Rhode Island in
> the States in the 70's discovered that one of the most potent allelopathic
> producers were cool season grasses; rye, bluegrass, fescue, et. al. and
> that the most common effect of these allelochemicals was on woody
> plants......
>
> I have recently lost some newly planted Celtis
> >australis
>
> I used to take classes to local places where, by chance, architects had
> designed in bunches of trees, some in turf, some in bare soil. It was
> always an eye-opener. There would be a line of trees, all obviously
> planted at the same time, yet the turf-encumbered trees were generally half
> the size of those in bare soil. Competition accounted for some of the
> difference but allelopathy produced most of the contrast. The grass was
> clearly secreting substances (still unidentified) that were killing
> roothairs of trees. The same effect can be observed if you grow several
> trees with varying amounts of grass-free areas maintained at the base of
> each tree. The bigger the grass-free patch the faster grows the tree.
>
> I should add, however, that allelochemicals are highly soluble. I.e., the
> harmful effects usually leach away after a couple waterings. *However*, if
> one were conscientious and adding new clippings all the time you could
> easily kill off a young tree.
>
> Ironically turf allelochemicals are a public hazard in the US. California
> passed a law some years ago mandating that municipalities reduce their
> waste stream by 50% by the year 2006(I confess I'm vague on those numbers,
> someone more knowledgeable should correct me) and the principal target for
> most cities has been lawn clippings. Not only do they form one of the
> largest components of what people throw away but they poison waterways with
> concentrated leachates. Most counties in California have funded public
> agencies designed to encourage backyard composting; again the idea is to
> reduce waste, especially, ta da, lawn clippings.
>
Gary Matson said
> The only caution I have regarding grass clippings is the potiential for
> importing damaging quantities of herbicides along with clippings from
> recently treated lawns. Hopefully it is not as common in Spain, but the
> use
> of 2,4,D and other broadleaf herbicides is common here and insidious in
> such
> cutely-named products as 'weed and feed'. While these chemicals will
> degrade fairly rapidly (so we are told) in composting conditions, the
> raw,
> recently treated clipping can carry some along.
>
> Other than that, drying the clippings first converts them into
> essentially
> very short-cut, high quality hay, and eliminates sticking and matting in
> most cases. Tremendous nitrogen release as they decompose, and great
> fodder
> for the soil fauna, especially come winter and the re-awakening of the
> night-crawling worms.
> --
> Gary Matson Far Northern California (with a climate very much like
> central Spain)
> http://www.plantstogo.com
> Adapted Plants for Hot Summer Climates
>
Gary Matson said:
> I guess I must politely disagree with Susan's statement in this circumstance.
>
> It is my understanding, both from my reading in matters horticultural, and from
> personal experience with all kinds of mulch including fresh pine shavings, wood
> chips and high quality hay, that organic matter of any kind when just placed on
> the surface as mulch causes little or no nitrogen 'drawdown'. This is largely
> because there is no significant mechanism for transfer of nitrogen up out of the
> soil into the mulch. The mulch may, if very high in carbon relative to nitrogen,
> intercept small inputs of nitrogen from above moving into the soil (as bird
> droppings, spent spider dinners, lightening-fixed nitrogen, air pollution etc.)
> until the mulch can be broken down, at which time the inputs are released. So,
> even if grass clippings were low in nitrogen, they should cause no problem if
> placed on the surface.
>
> But grass clippings are very high in nitrogen. There is more than enough nitrogen
> in them to allow complete decomposition without any additional input needed. In
> fact, if grass clippings are too high a proportion of a compost mixture it can
> cause problems with ammonia release as the overabundance of nitrogen is not needed
> by the microorganisms. The municipal composting operation in the small city near
> us has had this problem since grass clippings are the majority of their
> 'greenwaste' in the summer months.
>
> The clippings have essentially the same nitrogen content whether dry or wet, since
> the N is bound in cell proteins and such. As they decay, this nitrogen is
> released. This decay can be mediated by lots of different organisms from mammals
> through invertebrates to fungi and bacteria. The drying just changes them enough
> physically that they usually do not mat down. This is especially the case in dry
> climates like central Spain and interior California.
>
> Our vegetable garden nowadays is under permanent mulch, and is not tilled at all.
> Every year we go out and trowel in the transplants, then place a layer of several
> thicknesses of newspaper on the surface and then cover that with flakes of hay,
> peeled off of rectangular bales and placed as tiles all over the area. Usually we
> get alfalfa-grass mix hay, but some years it is just various pasture grasses cut
> green, dried and baled, intended for livestock feeding.
>
> As the hay is wet by the sprinklers (all overhead water), the hay flakes expand to
> make a fluffy layer several inches thick, often as deep as 20 cm to start. By the
> next year, that has all disappeared and only a thin strewing is left on the
> surface, and weeds are again germinating. The decomposition of this hay layer
> provides most of the nutrients needed by the vegetables. Some years and with some
> crops, a slight addition of ammonium sulfate is sprinkled on and watered in
> sometime during the plants' growth. We do not add organic matter to the soil
> directly, but let the worms come up and drag it down in for us. The soil has
> become porous and friable in a way I would not have believed possible. (This is a
> stony,red, kaolinitic soil, with high content of iron and aluminum clays and a
> dense clay pan at a few feet of depth) I think the grass clippings should
> function in exactly the same way as the hay.
>
> I have never been aware of an allellopathic problem from anything I have used, and
> perhaps it is because, as was mentioned in another post (Jerry's I think--I've
> already deleted it from my machine), the substances don't persist very long.
> Concerns about allellopathy are more often expressed regarding living plants and
> their root exudates and leaf leachates. Living grass roots are especially
> inhibitory of trees and shrubs, I have read.
> -
> Gary Matson Far Northern California
> http://www.plantstogo.com
> Adapted Plants for Hot Summer Climates
