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Chipped Eucalyptus Wood and Leaves from Tree Trimmers

Contrary to public opinion, there is absolutely nothing wrong with using the contents of tree-trimmers chippers as mulch, even if the source is eucalyptus. All wood eventually rots and becomes part of the soil. Eucalyptus chippings make an excellent and low cost mulch. Not only does it often come free of charge, but also it is clean. It contains no weed seeds and it is highly unlikely to contain pesticides or herbicides which may not be true of mulch from other sources. Many folks suppose that eucalyptus wood or leaves will kill plants, but this is entirely untrue. The only time when wood chips or chopped leaves of any species, including eucalyptus, can kill plants is when folks unthinkingly dig these raw un-rotted materials into the ground. This practice can turn plant leaves yellow and may kill them because un-rotted wood will rob soil of nitrogen in order to rot and thus also rob nitrogen from plants. This will happen regardless of the source of the chipped wood or leaves. If you do not dig the chips into the ground but just let them lie on top as mulch, no harm is done. So definitely do not remove the mulch. Next fall you can put a layer of manure right on top as described below under clay soil. Just don’t dig it into the ground.

The only wood products that can be used safely as soil amendment, in other words dug into the ground, are products that have been fully nitrolized (i.e.: enough nitrogen has been added to them so they can rot) or, alternatively, they have been fully composted, which means largely rotted. So the answer to your question is that your trees will be fine with raw chipped eucalyptus wood and leafy products on top of the ground as mulch where they will slowly decompose and add goodness to the soil. Meanwhile, this eucalyptus mulch will greatly reduce the growth of weeds and help to hold moisture in the ground. (See page 29 In my new organic book for the exact amounts of nitrogen to add to raw shavings to make them safe.) No addiltional nitrogen needs to be added when using the chips only as mulch.

Comments

  1. I used eucalyptus chippings on top of a new lasagna type bed in a field where I’m planning to grow native california bunching grasses, lavenders, cleveland sage, kniphofias, matilija poppies and other deerproof plants. I was starting to rake it off but now after I read this article I’ll just rake it away from the planting holes when I plant next month. Should be o.k.? I put chicken manure down followed by cardboard to smother the grass, soil, then eucalyptus chips.

    • Yes, simply rake the wood chips away when you plant so they don’t get into the ground. Chipped wood mulch is fine on top of the ground as mulch where it gradually decomposes (rots) and becomes part of the soil through time. Think of the north woods where leaves fall, twigs and branches fall and rot and gradually it all becomes soil and once it rots it then gives off nitrogen that the tree roots can then pick up as food. Thus in a sense a tree can grow in a forest on its own refuse. The same is true in gardens. We only need to remember not to dig this dry stuff (wood chips and any uncomposted, unrotted organic mulch) into the soil. If we dig it into the soil it then subtracts nitrogen from the soil in order to rot and this can kill plants. If mulch (wood chips, dried leaves, whatever) lies on top of the ground it cannot rob the soil of nitrogen and this has no affect on the plants. So, yes, you are okay to plant in your lasagna garden as long as you do not combine the un-rotted woody layers (in this case eucalyptus chips) with the layers in which plant roots are going to grow because if you do large amounts of nitrogen will be subtracted. If accidentally some chips get into the soil, you could add blood meal to compensate or any other source of nitrogen but it’s difficult to balance the amounts just right without burning roots, especially in an airy lasagna garden. Spoiled hay can also be used as mulch instead of chips as most books on this kind of gardening often suggest. Hay rots quickly and is a strong source of nitrogen and of course spoiled alfalfa is especially good. Horse owners are a source of this since the flakes of alfalfa drip stuff onto the floor and you cannot feed a horse with spoiled alfalfa if it is even slightly mildewed or your horse will fall ill. I also would like to mention that the water needs of the plants you mention may vary from one another. Red hot pokers (Kniphofias) are supposed to be drought-resistant but my experience with them is they need good drainage or they will sicken and die, but they also require plentiful irrigation in summer when they are flowering or they won’t ever bloom. In winter they can go dry but that’s when we have our heavy rains. I have not had much luck with kniphofias in Mediterranean climates, but they grow wonderfully in England and there they are considered “drought resistant”. They look as if they should be drought resistant but my opinion is that here they aren’t except in winter. So go figure! (I realize this is an opinionated comment and would be happy to hear from other gardeners on this point). Personally, I do not find kniphofias easy to grow in coastal zones of Southern California and wonder why they are so often touted as good things to grow when I don’t see any good ones in gardens? If one lives in Southern California I think Kangaroo paws (Anigozanthus) are a better choice since they bloom like mad and are perfectly adapted to our climate. They are not exactly the same shape, which loss I deplore, but kangaroo paws do point upwards with drama and decision and they come in lovely colors, bloom all summer with little care and are truly drought tolerant. Additionally, aloes come in many forms and all have spiky flowers similar to red hot pokers. Bloom of each species is brief but there are so many varieties to choose from you can have some in bloom all year.

  2. I just need to confirm that I understand this well, I have mulched my entire veggie garden with about 5in of eucalyptus and pine mulch as I was inspired by this gardening DVD I watched. I didn’t realise that his advise was that you can mulch just about any tree but eucalyptus as it is very acidic. Can I safely leave the mulch there and what are the long term effects as it starts to breakdown into to soil. Thank you

    • I read over your question twice to try to understand it. It seems as if you are asking me this question: Will mulching vegetables with eucalyptus and pine needles harm your vegetables? The answer is no, as long as you are just using these materials on top of the ground as mulch. (If that is not your question, you need to phrase it better.) A second part of your question seems to be will these ingredients in your mulch harm soil as they break down? The answer is No, but you must wait until they are fully rotted before you dig them into soil as soil amendment and that will take a very long time, perhaps years for the eucalyptus leaves. Pine needles are acidic and somewhat slow to rot. Eucalyptus leaves are oily and highly resistant to rotting, but they are no more acidic than anything else. So as you can see, both pine needles and eucalyptus are very slow to rot. They will not rot while lying on top of the ground in your vegetable garden for one season as mulch unless you grind them up into small pieces first. The important rule for you to follow is not to dig eucalyptus leaves or pine needles into the ground until they rot on top of the ground, and that is unlikely to happen this year. Thus you are fine. However, there is a very important rule for you to follow. Do NOT dig these un-rotted materials into the ground until they have fully rotted. You will know when that happens since then you will not be able to tell what they once were. This means that you must pull back the mulch before pulling out a spent crop such as the root of a cauliflower after you have harvested the head. Then you should amend the soil with compost and mix in fertilizer and plant something else, such as an eggplant in that space. After which you can replace the mulch. If you allow un-rotted carbonaceous materials such as eucalyptus leaves or pine needles to be buried in soil they will rob nitrogen from the soil in order to rot, as I have said many times. But as long as they lie on top of the ground they will do no harm whatsoever. Pine needles make an excellent path covering in vegetable gardens. I have often used them that way in mine and once they had fully rotted then it’s okay to dig them into the ground as additional soil amendment since they do no harm once fully rotted. Also, their acid composition didn’t harm my soil either since our soils in the west are alkaline and our irrigation water is alkaline also, so adding some acid organic materials is a constructive thing to do. Mainly, however, I have used pine needles from my trees as mulch around azaleas and camellias since azaleas and camellias are acid-loving plants.

  3. Sources of eucalyptus leaves

    • Your query “sources of eucalyptus leaves” is unclear. If you are asking me to provide the name of a source of eucalyptus leaves, I cannot do that. Most species of eucalyptus trees sprinkle their leaves onto the ground year round. They are messy trees and tree trimmers are often trimming them to reduce mess. Therefore in areas where these trees grow it is usually very easy to find sources of chipper materials from eucalyptus, often for no cost. Additionally, eucalyptus leaves and wood do not rot quickly or easily. The concern of most people who have eucalyptus trees is how to get rid of the leaves not where to find them. Mulch of eucalyptus leaves is not particularly desireable, but on the other hand not as bad as some folks apparently think, since it eventually breaks down. If one has used eucalyptus chips and leaves as mulch, there is no reason for removing it, as I said above. However, one should never dig or till un-rotted mulch of any kind into the ground until it completely rots so that one cannot tell what was in it in the first place. I incorrectly stated, or at least implied in the above post that every kind of wood and leaf from tree trimmers eventually breaks down and thus does no harm as long as it is not dug into the ground. Our Farm Advisor, Vince Lazaneo, read that information on my blog and emailed me to say that is not entirely true. Vince pointed out that black walnut and English walnut wood, bark, and leaves should never be used as mulch or as ingredients for soil mixes since the residue of these trees contains chemicals that kill other plants. So do not ever use leaves, bark, twigs or chipper materials that come from English walnut or black walnut trees as mulch. I forgot to mention another woody product one should never use as mulch is chipper materials from pecan trees. To quote our recently retired Farm Advisor, Vince Lazaneo, “Black walnut and English walnut and also pecan have a compound that inhibits the growth of tomatoes and a variety of other plants.”

  4. Sharon Muczynski

    Your advice is awesome Pat!

  5. Pat,
    We have recently acquired a lot of eucalyptus mulch (leaves and chips) and were wondering if it is harmful in any way and what procedure we have to go through to detoxify it? We were just going to spread it all over our gardens.

    • It’s fine to use eucalyptus chipped wood and leaves as mulch. You don’t need to detoxify it and it’s not harmful as mulch. What would be harmful would be if you dug any of it into the ground. If you do that it will try to rot and in so doing will subtract nitrogen from the soil in order to rot. This is what can kill plants, but lying on top of the ground around plants does no harm whatsoever.

  6. Thanks for the clear information re: eucalyptus mulching. This means to me to keep it out of composting completely.
    I wonder if you have any information on Silk Oaks (Grevillea robusta) I have kept those leaves and wood out of both mulch and compost due to its allelopathic, growth inhibiting properties. Is my information correct or can I use this in mulch and just keep it out of composting?

    • Despite the allelopathic effects of silk oak leaves, they will gradually decompose in the same way as eucalyptus leaves will do so. I once had a silk oak tree and there is one across the street from me. Though for a good forty years, the leaves of the tree across the street were never raked up and allowed to rot where they fell, that ground is now being used for growing vegetables and flowers with no ill effects. So I would go ahead and use them as mulch. However they are messy and do not lie down flat the way eucalyptus leaves do. Is it possible for you to put them through a chipper? Or perhaps you can spread them in places where they will not be an eyesore.

  7. Hello Pat,
    I have read through our answers to eucalyptus mulch and I know I seem silly, as I am new to Aus and would like to verify something please.
    We have, sadly, had to bring down an enormous Bloodwood and have loads of fine mulch now. My question is if I spread this mulch over my broadleaf lawn will I kill off my lawn?

    I look forward to your reply as I hope I will not kill off my lawn that I have been trying to keep content.

    Regards

    • I recommend eucalyptus mulch for covering paths and flower beds, or even the paths within a vegetable garden. However, I do not recommend using it to mulch a lawn. The safest thing for mulching lawns is ground conifer bark or ground conifer wood. (in other words pine, redwood, podocarpus or cypress.)

    • No, you don’t seem silly. Though I answered your question I can see why you did not understand my first reply. I couched my answer carefully so it would be completely true. Thus I did not say yes or no to your question. Here is the problem: I cannot say yes or no to your question because so far as I know no scientific studies have ever been done on this question, so I am sticking my neck out here. Out of an abundance of caution I am going to say no, do not mulch your lawn with eucalyptus mulch and below you will read why I am saying this.

      If you put a woody mulch or raw sawdust from any tree all over your lawn and lay it on thickly you could kill or smother your lawn, depending on the variety of grass and the time of year. Additionally, if the mulch slowly combines with the soil, there is a real danger that your lawn could be killed or growth could be severely slowed down by lack of nitrogen. The reason for this is that if woody or carbonaceous materials are combined with garden soil, they rob nitrogen from the soil in order to rot. My suggestion is that you cut the lawn short in autumn and then mulch it with aged animal manure, such as aged cow manure. The grass will grow up through the manure and be fed. This is a great way to improve a lawn.

      Use the mulch from your tree in a different way. Pile it up and mix it with nitrogen such as sulfate of ammonia, also called Ammonium sulfate, and keep it wet. Ammonium sulfate is a strong nitrogen fertilizer and it is not organic and easily can burn plants if not applied correctly. When mixed with wood shavings, however, this strong nitrogen fertilizer will gradually rot the wood and make it safe to use as soil amendment. The rule of thumb for this task is: Combine one and one-half pounds of actual nitrogen with every 100 pounds of raw sawdust or shaving. Then you can safely use it anywhere in your garden, even as a soil amendment.

  8. My eucalyptus tree came down in the recent storm we experienced (Sri Lanka) and I was looking for ways to use the wood … when I came across this very informative post and a great site.
    Unfortunately I do not have a chipper machine though I have been toying with importing one (not available here can you imagine !!!) but they are pretty expensive. Will keep looking for a domestic version and will be using wood for larger projects. Meanwhile … keep up the good word Gardener !!!!

    • Thank you for your kind comment. I have often wanted to go to Sri Lanka ever since my teens after reading a wonderful novel about it and the elephants in those days that lived in the forests on the hills.

      I once had the remains of a giant eucalyptus on my property. The tree had been cut down at some prior time, much of it had been hauled away, but the huge trunk and the stubs of branches lay sideways on the ground in a sort of depression on a bank. For many years I planted around it and used it as a landscape feature as if it were a large rock in a rock garden. By now, 60 years later it has mostly rotted away but there are still some remnants of it left in what is now a succulent bank, planted with tree aloes and many other succulent species in all sizes arranged in big drifts, flanking one side of my driveway about 100 feet long and 25 to 30 feet wide.

      On another occasion after having a tall eucalyptus cut down, I had the logs piled side by side and two to three logs deep in such a way that they formed a fence on the upper edge of a bank at the bottom of our property and between the road and our house. This log fence protected my children and the area where their swings were located. Later I added wandering paths on the sloping ground. Eventually the logs rotted away. Today that area is filled with a thick plumbago hedge that goes down to the road and inside the hedge which we keep sheared, the flat area where the swing used to be is now a brick patio shaded by a 20 foot long pergola. Closer to the house is a large terraced garden that was once my TV set.

  9. Pat, I have 2,000 acres of growing eucalyptus trees that were “donated” to me when MeadWestvaco ended their 10-year growing study in southwest Louisiana. (MW was acquired by another company and they elected to walk from this study). Any idea of a source I may turn to in order for the trees to be removed?
    Much thanks,
    Mark

    • I live in Southern California and my subject is Mediterranean gardening. I would suggest you try to have the trees cut down for firewood. Unfortunately there is no other use for eucalyptus trees that have been grown in the USA due to the twisting of the wood inside the trunks.

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