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.
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Your advice is awesome Pat!
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.”
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.
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.