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Steven Lauwers
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Joined:
18/05/2013
Last Updated:
19/05/2013
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Riversdale, Western Cape, South Africa
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Semi Arid





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Allelopathic nature of Eucalyptus Globulus

Posted by Steven Lauwers about 9 years ago

Our new home is surrounded by blue gum trees (Eucalyptus Globulus) and all of our neighbors have indicated that absolutely nothing grows under these trees. Sounds like a challenge

There are many articles written about the allelopathic nature of Eucalyptus trees and many discussions are found on the internet's forums. According to the most articles Eucalyptus provides a toxic environment which prevents the germination of other species. However non of the researches seem to be conclusive. Therefore we took up the challenge to create a small vegetable garden right under the barren soil of the Eucalyptus trees. We decided to plant directly from seeds and have chosen to plant the following vegetables: lettuce, fennel, peppers, tomatoes, Swiss chard, onions, pumpking varieties and some flowers such as tagetes.

We did not plant directly in the soil but first created a hügelbed in order to maintain as much nutrients and moisture in the soil. The test garden is about 5 square meter in size.

As we are living in a semi-arid environoment we decided to water the small garden. We initially gave 25 liters of water per day and after 3 weeks (when the seedlings were established) we reduced the watering to 25 liters 3 times a week.

Well, for people who still believe in the toxic nature of the Eucalyptus tree, have a look at the pictures below. We have been enjoying delicious tomatoes, fennel, lettuce, peppers and pumpkin  from our garden. 

In our modest opinion the only issue that exists with Eucalytpus trees is that they use all of the moisture in the soil. So with the necessary water retention techniques there should be no inhibiting reasons for growing anything under a Eucalyptus tree.

Tuin voor Tuin na2 Tuin na3 E globulus1 Tuin na4 E globulus2 Cottage2 Tuin na2 E globulus2 E globulus3 E globulus4

Comments (9)

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Carolyn Payne-Gemmell
Carolyn Payne-Gemmell : Hi, I am curious, are you saying the trees in the first photo are E. globulus. They don't really look like it to me, can you put up a photo of the seed pods and maybe a close-up of the leaves or an individual leaf. I have grown and watched the progression of E.globulus over 13 years from seedling to 30m specimen. E.globulus have a very straight single trunk and many small horizontal branches for the first ten years or so, so they make quite a thick windbreak. Then as they mature you can knock off these small twigs and open the understory a bit. There are two main reasons things don't grow well under Eucalyptus species, the first is they prefer a fungal soil and have root association which are hostile to some other types of root association fungi of other species, but you are probably compensating for that with manures or a bacterial compost. The second thing is that E. species drop quite a lot of oil and waxy substances onto the plants below them, this mostly happens as rain falls through the tree canopy. Moisture under E. species is a big factor no doubt, but you might find with time the drip line feeder roots will heave themselves to the surface to get this easy bounty of nutrient and water. I would say in the long term the section of bed 4-5 mts out will work ok, as I had Apricot trees at this distance, but then again they didn't mind the fungal soil. You probably are not having as much of a problem with the oils and waxes as your trees are either a species which does not have as much as E.globulus and are possibly a species which doesn't have as dense a leaf canopy and therefore surface area. Also, you may have only had this bed going for one summer season and haven't had the rain washing the oil and wax onto the plants underneath. Sorry if that all sounds a bit negative, you have obviously been growing food there. I have a bit of an idea for the future for you, that could help in multiple ways. You could convert this row of trees to a pollard or coppice as whichever E. species you have they would be reasonable firewood. And getting them down in height will limit the blow off area when the rain and wind hit them, limiting the oil and wax spread. Reducing the canopy height will cause the roots to prune a bit too and therefore shorten their reach. The windbreak created by the multiple branching as the tree regrows will be of the most benefit to you, as I think slowing down summer winds, reducing evaporation is as important as anything else. I would shorten every third tree for three years (eg, tree number 1, 4, 7,etc the first year, 2,5,8, the next year and 3,6,9 the third year etc)so you are not taking down the canopy all at once, and then see after that how it goes, but maybe keep a tall one at the end of the row for bird habitat. Just a thought anyway, best wishes, Carolyn
Posted about 9 years ago

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Steven Lauwers
Steven Lauwers : Hi Carolyn, the first photo might be from a bad angle to show the real extent of the trees. I'll post some more pictures, including leaves. I'm definitely no Eucalyptus expert but as E. Globulus is the most common species in South Africa, it is probably this one. Expect an update a bit later on.
Posted about 9 years ago

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Carolyn Payne-Gemmell
Carolyn Payne-Gemmell : Hi Steven, if you like, send me your email address through the 'contact this user' tab. I can send you some photos of the growth habit and identifying features of E.globulus.
Posted about 9 years ago

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Carolyn Payne-Gemmell
Carolyn Payne-Gemmell : Hi Steven, thanks so much for the extra details. Your trees are definitely not E.globulus.

Blue gum has the following characteristics, the immature stems and the leaf vein is yellow and the flower buds are in the leaf/stem axis and are single.

I strongly suspect you have Eucalyptus camaldulensis which is the River Red Gum, as it has the red stems and leaf vein in your picture, and has its flowers in clusters out on the ends like the buds in your photo. Another bit of a clue too is that the bark on yours is whitish with grey patches, this is common look with E. cameldulensis, but it does apply to many E. species. Have you ever seen the colour of the wood? River Red Gum is very reddish brown and is very dense. Blue Gum wood is a lighter yellowish brown and is not as dense in comparison, a little more flaky or fibrous looking.

If it is River Red Gum, I can tell you it is the BEST firewood you can have, hot and long burning. The most marked difference between the two species is the growth time. Blue Gum is very fast and River Red Gum is very slow. A 10year old Blue gum would be around 40 to 50 cm diamater across the trunk and the same time for the River Red gum I would expect a trunk less than 20 cm diameter . Of course that is dependent on rainfall, but that is a good comparison of both from my land in Victoria, Australia.

I will do a little more research and just check what other E. species are in South Africa. Yours Abundantly
Posted about 9 years ago

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Steven Lauwers
Steven Lauwers : Hi Carolyn, Thanks for this great information and based on your feedback it could well be that it is indeed E Camaldulensis. Growth is not that fast, the bark resembles it definitely and it's extremely dense wood which makes it ideal for fencing poles. However, the color of the wood is definitely not reddish brown (I have added some images of the wood color) when freshly cut but this might change when it dries out. Unfortunately we had to cull some of the trees to provide sun to our solar system. Although Eucalyptus is considered an invasive species in South Africa, culling a tree is still one of the most difficult things to do. We are hoping to use the wood for good purposes such a growing shitaki mushrooms on some logs, creating furniture, fencing poles and get some fantastic firewood. At least the live of the tree will have had a benefit and we'll remember it whenever it is used.
Posted about 9 years ago

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Carolyn Payne-Gemmell
Carolyn Payne-Gemmell : Hi Steven, looks like I better go back to my research! It is not River Red Gum either, as Red gum has wood coloured like a rusty brownish red to deep pinkish red, but at least we can rule out what your trees are not. There are something like 700 Eucalyptus species in Australia and luckily only a few are in South Africa, so we will work it out yet. You have put up lots of good clues so that helps, the main thing that will prove the positive identification beyond all doubt is the flowers themselves, but the trees are probably not flowering at the moment. Going back to my first comment, I think these trees are mostly too old and large to coppice without killing them, but if you can collect some seeds they grow easily, and you might be able to grow a dedicated coppice for firewood and poles etc. Are there any seedlings coming up anywhere? You can transplant them if they are under about 20 cm tall. Yours Abundantly
Posted about 9 years ago

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Carolyn Payne-Gemmell
Carolyn Payne-Gemmell : Hi Steven, my latest best guess is E. Cladocalyx , Sugar Gum. Are there any mature seed capsules lying around?
Posted about 9 years ago

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Steven Lauwers
Steven Lauwers : Hi Carolyn,

Sorry for the late feedback. I have been on a trip to Europe for the graduation of my son. I will try to make a picture of a mature seed capsule and post it for you. Btw, it has been raining a bit while we were gone and it turns out that the wood has become reddish brown from the moisture.
Posted about 9 years ago

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Carolyn Payne-Gemmell
Carolyn Payne-Gemmell : Hi Steven, no worries at all, I have been flat out busy myself and I haven't had a chance to take any photos for you from my end either. At least with this little bit of work you will be able to confidently identify Eucalypts in your part of the world, that could be very handy. Even though they are considered a pest almost everywhere in the world, if you can understand the "Inherent" characteristics of the ones available to you and your community you will be able to make the best use of them and manage them for maximum output. There are some Sugar Gum plantations in my area but I didn't think it was that initially, as the bark here often has lots of orange patches as well, but that difference could be caused more by a climate variation than anything else. I will get under one of these plantations and take a photo of the seed pods too, plus I need to get a good photo of just how amazing the colour of River Red Gum is. Yours Abundantly
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