Thursday, October 18, 2012

Silky Oak

Grevillea robusta
Family: PROTEACEAE
The silky oaks are just beginning to come into flower.
We can expect to see them continue their spectacular display for much of November.

With a bit of careful planning they can be among our finest landscaping trees. Not suitable for small gardens, they are best used for acreage, highway, and park planting. They also make very good street trees - provided the streets are rather roomy. They co-ordinate wonderfully with the scarlet flowers of the flame trees (Brachychiton acerifolius), another spectacular local native plant that flowers at the same time.

Silky oaks are fast-growing and live for 100 years or more. They are drought hardy, and cope with frost to -4° even when young.
However, their large, shallow roots can be problem,  interfering with built structures, and travelling a long way for water. Ideally, the trees should be should be planted 5 metres away from concrete footpaths and 15 metres from underground pipes.


 They are deciduous in spring, with new leaves appearing as soon as the old ones fall. The impression given is that the younger generation are pushing the oldies off the tree.
The fresh leaves are a pretty shade of green, with silverybacks that show off in the wind.


In this country where deciduous plants are not common, trees which dump all their leaves in one go are regarded by some people as too messy for words. However, they do provide a wonderful “mulch opportunity”, especially as the intricate shape of the leaves means they don’t tend to blow all over the place, like the leaves of some other deciduous trees. Once positioned as mulch they tend to stay put. (I  pick them up from the lawn with a mower, and use the nutrient-rich grass and leaf mix on the garden).

Silky oak flowers are fascinating.

Each flowerhead might have as many as a hundred small flowers. At first glance, each one seems to consist of nothing much but a long style. This is the female part of the flower. The little green knob at the end is its stigma. It’s eventual female role is to catch pollen and pass it along to the ovary, a second little swelling lower down on the style, where the egg cells await fertilisation by the pollen.
New flowers are functionally male. The style is curved in a loop, and the stigma - not yet mature and sticky - is held firmly in a socket formed by the tip of what looks like a single little petal. As the flower begins to mature,  the “petal” breaks up into four tepals, and the four pieces of the opened-up socket are each revealed to have an anther on the inside.  This is the male part of the flower, now mature, producing pollen, and firmly in contact with the immature stigma.
The style straightens out, revealing the pollen-covered green knob of the stigma. At this point the female part of the flower is unable to be fertilised, and simply acts as a pollen presenter. It holds the pollen out there where it will rub off on the feathers of visiting birds which are attracted by the copious flow of nectar that each flower produces at this stage of its maturing process.
As the birds move around feeding on the flowers' sweet bait, the they carry the pollen about with them, much of it reaching stigmae of flowers which are at a later stage of development. The male part of those flowers has retired. It no longer makes pollen, and the flower is now functionally female. The stigma is now sticky and catches pollen from passing birds. Some of it makes its way down a pollen tube to the flower's ovaries.



 This photo shows the three stages of the flower. (Click to enlarge for a close look.) In the first (male) stage, the stigma is head-down among the fertile anthers, being dusted with pollen.  In the middle stage, the style has straightened out, and the stigma is liberally coated with pollen, presented ready for birds to take away.  In the last (female) stage, the stigma has become sticky and is ready to catch pollen and pass it down to the ovary. When  fertilisation has been achieved and the tepals fall off, the style begins to shrivel and the ovary swells to become a seed capsule.



The photo above shows a flowerhead fresh with newly opened flowers. Click to enlarge, to see the generous nectar flow that has suddenly appeared at the base of the styles. The tepals are clearly marked with red nectar guides, advertising its presence to the mobs of shrieking birds which descend on the trees for the feast.
The result is that pollen is scattered about rather wildly. Some pollen grains stay close to home, fertilising more mature flowers from the same tree. Some is spread to other plants. Grevilleas are well-known for their ability to cross-pollinate, even between different species.
In the old days, Aborigines used to make a sugary drink from silky oak flowers, dipping the whole flowerheads into water to wash the nectar off.
Silky oak timber is among our finest of cabinet timbers, with its warm honey colour. It is usually quarter-cut, to show off its silky rays.

Grevillea robusta and Allelopathy
Silky oak seedlings don’t thrive under parent trees, and it may be that they are suppressed by an allelopathic chemical produced by their roots.  I notice that many overseas internet sites claim that Grevillea robusta’s allelopathic effect kills off “the saplings of all other species”. This doesn’t seem to be the case in my garden or in our local rainforests.  In both cases it grows in close harmony with other plant species.
Claims about the allelopathic attributes of various plants are rather fashionable at present. In some cases they are true. In others, they are premature, the scientific research having not been done. Fast-growing trees can also suppress other plants by more efficient use of the available soil nutrients and water, and by shading them out with their canopies or their carpet of mulching leaves. This may be the real cause of some of the sweeping accusations of allelopathy. (An allelopathic plant usually has a different effect on different plants, with some species being suppressed, while others are actually improved.)
It wouldn’t surprise me, however, to hear that silky oak allelopathy suppressed other Proteaceae, and some research showing that it suppresses wheat may also mean that it suppresses grass (though I find that kikuyu grows well around the base of one of my trees).
I would be interested to hear from my readers about their experiences with growing plants near silky oak trees.

56 comments:

  1. I have a sizable silky oak, looking for bee attracting plants to plant underneath it, I was thinking about trying lavender?

    ReplyDelete
  2. Hello Timothy.
    I am wondering why you particularly want Bee attracting plants. Is it for the honey, or do you just want bees on your silky oak?
    I don't know where you are in the world. (Such is the nature of the internet.) But if you are in Australia, your tree will attract birds in the honeyeater group every year when it flowers. These are its main pollinators, so they will help the tree make seeds,

    ReplyDelete
  3. To continue from the above: the seeds will then attract a second flush of seed eating birds. The flowers will also attract nectar-eating insects of many kinds, including butterflies and plenty of bees ( provided there are hives around).
    Of course if you want lavender, you could give it a try. However silky oaks have rather greedy roots, so some plants don't do well under them. I find small wattle species good. They give a floral display in another season, amd provide bees with useful pollen.
    Best of luck, whatever you choose. Perhaps you could let us know sometime, how you go.
    Cheers
    Trish

    ReplyDelete
  4. I have a Large Grevillea Robusta with limbs down to ground level. When is it safe to prune these off without damaging the tree?

    ReplyDelete
  5. Hi John.
    These are very tough trees, and you should be able to prune them any time.
    It's not a good idea to prune a tree in a very humid, rainy period, as this can let fungi in. Not usually a problem in our climate, though. It is only when there are weeks of continuous wet that a problem happens. Similarly, leaving a very slight overhang (cutting on a slant means you are not left with an upward-facing cut surface which might collect water as it heals around the edge. (The healing process results in a raised ring of woody tissue.)
    Remember to leave a bit of a collar - just an inch or so of limb - rather than cutting it off flush with the trunk. The very base of the branch contains vigorous tissue which will grow more quickly across the wound. This protruding bit will eventually vanish into the trunk, becoming a neat scar as the tree grows.
    And just a thought. Some people like to have a few lower limbs left as a nice bit of casual seating in a shady spot, or to make it a good climbing tree for the grandchildren.
    Trish

    ReplyDelete
  6. Hi there. We have built deep vegetable garden beds. I read you could fill the bottom with branches of trees before layering with cardboard, mulch and soil. Would silky oak branches with seeds cause issues with seeds gerniating later? The branches are 40 cm from what will be the top layer of soil.

    ReplyDelete
  7. Hi Shannyn.
    The answer is that they wouldn't provided they continue to be 40cm deep from the top (or any gaps in the side).
    Seeds don't normally germinate unless they are near the surface.
    Even if they did germinate as a result of future turning over of the soil,they are not likely to be a problem as they are very easy to weed out. You might get a few in the future, as the soil layers settle over time, and you turn the soil by pulling out deep-rooted veges, but I don't think you need to worry about them.
    Trish

    ReplyDelete
  8. Hi, i have three silkyoaks growing in my yard (Toowoomba/Highfields area). They are each about 6' tall, however I dont like where they are positioned. Would you offer any advice about moving then to other locations?

    ReplyDelete
  9. I have no knowledge about how well these trees cope with being moved, However, moving trees once they are past the small seedling stage is a risky thing to do. It is not possible to do it without damaging their roots, and a decision to take the risk may come back to bite you years later. Trees whose roots are not in excellent order may never develop a strong enough root system to do their job of holding up the tree properly.
    My advice is to destroy these trees and grow new ones. Why risk having the trees fall and cause damage in future years when it won't really take very many years to replace 6' growth, with this fast-growing species.
    The best results come from planting very young trees which are planted from small tubes, and never allowed to become even slightly pot-bound.
    Trish

    ReplyDelete
  10. I have been doing some landscaping around a very large silky oak in my backyard. Unfortunately, the contractor decided to cut a very large root quite close to the trunk, maybe 1.5 trunk widths away from it. The root is very large and I am worried that the tree is now unsound and in danger of tipping over. Should I be worried. The trunk is perhaps 600mm, and the root perhaps 250mm.

    ReplyDelete
  11. Hello Tom.
    It is frustrating, isn't it, when people behave as though roots are somehow irrelevant to the health and structural strength of the tree.
    I am sorry, but I can't give you advice on whether this has made your tree unsafe. I can comment that the trees seem to have strong roots, which could mean that the tree would manage without one of them - even a big one like that.
    However I'm afraid that the decision as to whether the tree is now safe enough for its situation, that is something only you can decide. You might like to take into consideration things like the prevailing wind direction (obviously loss of a root on the upwind side will make it more vulnerable to being pushed over) and which direction the tree is likely to fall if it goes. What would be damaged if it went.
    Sorry I can't be more help.
    Trish

    ReplyDelete
  12. Hi Trish,

    Thanks for this invaluable information - regarding silky oaks and so many other useful local gardening topics included on your blog.

    I am currently looking for a tree to replace a tall conifer (a cedar variety, I think), that was cut down from a row of the same species along our back fenceline.

    I was considering the silky oak as I have seen it all around the Toowoomba region and believe it would fit the available space very well, however I do have some concerns regarding root interference with water pipes.

    Would you have a recommendation of another similar-sized native, dry rainforest type tree that might prove less problematic to our plumbing system in the long run?!

    Thanks for your time,
    Steph

    ReplyDelete
  13. Hi Steph.
    Can I assume you live in the Toowoomba area? Have you thought of another conifer? Hoop pines do very well in Toowoomba. Or if that seems a little too large,you might like a Bailey's cypress (Callitris baileyi). It is an endangered species so we should be growing more of them . Other biggish trees that might suit you could be one of the Flindersia species. Crows ash (Flindersia australis), leopard ash (Flindersia collina, or the very fast growing Long Jack (Flindersia xanthoxyla).
    Hope this helps.
    Trish

    ReplyDelete
  14. Hello,
    I have been given around 10 Silky oak seedlings of varying sizes from my parents. They have just grown from seeds that have dropped from their own silky oak. We have 10 acres near Maryborough and would like to plant them. I was just after some advice as to positioning. I was thinking they would be nice in a bit of a line with some distance between them for privacy without completely blocking out our view. Thinking of distance from fences etc. Most of our neighbours are a fair distance from the possible planting site, and the two that are the closest would be at least 20 metres away. Our neighbours dam is reasonably close and I know S oaks will search out water, so not sure if this will be a problem. The area I am thinking is facing east and is on a gently slope away from our house.
    Any thoughts would be appreciated.
    Thanks
    Maxine

    ReplyDelete
  15. Hi Maxine.
    Sorry for my slow response. I have been away, and coping with blog comments on my phone is a step beyond my technological know-how.
    Your site sounds ideal for silky oaks. As you say, it is good to consider their water-seeking habit, especially where underground pipes are concerned.
    You should also consider their shallow roots, which can damage concrete paths. In theory they could also damage building foundations, though we do have one only 3 metres away from a shed, and there is no evidence of harm.
    The other thing to consider is winter shade. If you plant a row of any kind of tree, they will make shade to the south, which is a broader band in winter when the sun is lower in the sky. So you shouldn't plant them where they will shade the sunroom of your house.
    However, on your size of block, I don't think you can go wrong.
    You might like to consider putting in a few flame trees at the same time (if you live in a place with nothing more that rather gentle frosts)as the two will flower together and will be quite spectacular at some time in the future.
    All the best,
    Trish

    ReplyDelete
  16. Our silky oak has started dropping all its leaves at once in September in Florida. The one right next to it hasn't lost any of note. Any idea what is going on? Has it just gotten confused by weather? or might it be dying of something? There are no other visible signs of illness. Thanks!

    ReplyDelete
  17. Hello anonymous from Florida.
    I don't really think I can help you, as my knowledge of silky oaks (and other plants) is purely of plants native to my part of the world, as they grow here in in our local ecosystems and in our gardens. This is my personal hobby and the raison d'être of my blogsite.
    You are right that leaf-drop in autumn doesn't sound right for the species. Here in Australia we would expect silky oaks to do their leaf drop in spring, in sync with all the others. They are doing it as I write.
    It certainly sounds as though what you have is a dying tree, but I have no idea what factors might be causing it in a situation which is so far away, both geographically and ecologically from the situation I am familiar with.
    Sorry.
    Trish

    ReplyDelete
  18. Hi Patricia, I have a silk oak that is about 5 metres tall and has been in the ground at least 7 years. It does not flower. I’m unsure whether to cut it down or give it another year? I am on acreage inland victoria and soil has a lot of clay, the tree faces north. I bought the tree at a market and was approx 60-100cm tall when planted. At the moment the leaves are a little yellow. Cut it down??

    ReplyDelete
  19. Hi Herta.
    No, don't cut it down!
    The lack of flowers so far would be because it grew from a seedling,(which means good, strong roots - just what you want in a tree). Most nursery-grown plants come from cuttings, which means earlier flowering, but potentially weaker roots.
    The nursery industry uses cuttings to produce so much of its stock that it has taught us that flowering from a young age is normal, but this is not how nature works.
    It is normal for silky oaks to lose their leaves at this time of year. Very young trees don't do it, though, so the yellowing of the leaves this year is a sign that your tree is maturing, and ready to start dropping its leaves every spring. After the spring leaf-drop, silky oaks then grow a complete crop of beautiful new leaves at once. It is almost as though the new leaves have pushed the old leaves off. The leaf-yellowing may be a sign the tree is now mature enough to flower this year. If not, it won't be more than another year or two or three. The flowers come in October-November up here in Queensland, and must be somewhere around that time, or maybe closer it Christmas, in Victoria, so you may be lucky and get some this year.
    The annual crop of dropped leaves makes wonderful mulch. The older the tree, the more mineral-rich the leaves. Their shape makes them interlock, so they don't blow around the way some other dropped leaves do. As the years go by, you will probably find yourself looking forward to to your tree's once-a-year gift of free mulch.
    All the best,
    Trish

    ReplyDelete
  20. Hi Trish,
    I'm in a bit of a dilemma... I live in a suburb of Brisbane and have a large silky oak robusta on the nature strip. It's doing great and we're a big fan of the species. Unfortunately about 2 years ago I noticed a small sapling growing right next to our water tank and house (approx. 1m from the side of our house and the adjoining boundary fence). Of course before I knew it, it had quickly grown and now stands about 2.5-3m tall... we have been pruning it in the hope we can keep it maintained but I'm concerned that given the small area it's in and close proximity to the water tank and house it could eventually cause issues given its root system etc. My dilemma comes in not wanting to remove a beautiful, healthy tree. Is it possible to keep this tree small or should i err on the side of caution and remove it now? Many thanks, Kerry

    ReplyDelete
  21. Hi Kerry.
    I'm sorry to say, I think you should get rid of it at once.
    I quite understand your dilemma. Like you, I hate to kill a good healthy plant, especially if it is also a beautiful one. However, you also have to protect your tank and your house. They would cost a lot more to replace than the silky oak would!
    If you get another seedling, you might like to pot it up while it is small. They make lovely pot plants.
    Trish

    ReplyDelete
  22. Many thanks Trish... i am grateful for your reply. I am kicking myself I didn't remove it and pot it when I first noticed it. Yes, it's a horrible decision to make. :0( I'm wondering if shrub grevilleas that are a lot smaller would grow as well as the silky oak. We need some screening along our boundary and I am a big fan of the grevilleas that grow to 2m maximum...

    ReplyDelete
  23. Hi again Kerry.
    As you would have noticed, the topic of my blog is the native plants of the basalt soils (red and black) of the Toowoomba district. These are the plants that interest me, and the only ones that I make a claim to know much about. This is a large area, but has no native Grevilleas other than the silky oak, so I don't like to comment on the characteristics of other grevilleas. I know no more about them that anyone else.
    All I can say is that they can indeed be grown in a wide variety of habitats where they don't occur naturally(including Toowoomba). To me it seems worth giving them a go, but you would do better to ask about them at your local nursery - or perhaps talk to someone in your neighbourhood who has them in their garden.
    All the best.
    Trish

    ReplyDelete
  24. Thanks so much Trish. I'll certainly have a chat to the local nursery.
    Cheers,

    ReplyDelete
  25. Hello and thanks in advance Trish, you are a wonderful treasure of learned knowledge.

    My Mum lives in the suburbs West of Brisbane and as a child a Silky Oak has been left to grow and stand in it's place as people and birds have come and gone.

    Mum has found a sappling emerging in the dirt under her house that is on metre high concrete stumps.

    On a side note, some few years ago, she also found under the house a Mulberry that I replanted a few years ago that hasn't sprung any fruit as yet.

    Anyhow, I live approx half way between Gympie and Maryborough, typically dry Schlerophyl country, however in 74 it was massacred for a now failed pine plantation.

    With the considerations of space, growth ecetera, I think I have a place at the side of the front driveway, ( & magically I have 4 flame trees establishing along the front, ((still ot flowering after 4 years, but I am practicing patience)) where I see you suggest compliment each other well.

    Anyhow.....the ground there is volcanic red rock. Rubble and very tough. I have two Cycads in same space who albeit slow growing seem to be showing continued signs of life, and my main concern is the ompetition with a line of pine trees from the plantationthat are still left on the neighbours side. The environment I guess would be quite acidic already. Would this have any known adverse effect on the Silky Oak and would it establish AOK being transplanted as a re-established off shoot from under the house?

    Thank You Again,

    ReplyDelete
  26. Hi Jaime.
    I wish you luck with it. It could look great.
    However, I hope you are taking the size of the spreading surface roots into consideration. If you have it too close to the driveway it could make a nuisance of itself. I recommend keeping silky oaks 5 metres away from any built thing, so you can feel comfortable that it will not cause expensive damage.
    Trish

    ReplyDelete
    Replies
    1. Oh yes I have considered this..so would it be safe to assume that the main concern is the uplifting of foundations? In this case, the driveway is not concrete. Would it be less of a concern? And would the driving over deter the roots or perhaps even damage them?

      Delete
  27. Hi Jaime.
    Silky oak roots are very much surface roots. This means that half of the root sticks up above the ground. I just went out and measured a root of one of my trees. At 2m away from the tree is is 7cm above ground level. That's quite a speed bump. The tree is 40 years old, but had raised roots from quite early in its growth.
    I'm not sure how much driving over the roots would deter them from becoming raised surface roots like that, as it's not something I have tried. Our gravel drive is 3 metres away and there is no sign of visible root. Was it the driving, or is it that 3m is a safe distance? Roots don't like compressed soil, so maybe the tree has avoided that area. It is always hard to know for sure, with plants.
    Sorry I can't offer firm advice or exact measurements. The bottom line is that whether or not to plant the trees is something you will have to decide for yourself.
    All the best.
    Trish

    ReplyDelete
  28. I've been trying to keep my lovely robusta topiaried as it's within a metre of my house. I haven't the heart to remove it but now it's had a growth spurt and becoming harder to topiary. Trunk is getting thicker too. Will break my heart to have to remove.

    ReplyDelete
  29. Okee doke. Thanks Trish for your insights and suggestions.

    I will pot it and ponder. Maybe send a pic when it's grounded.

    Thumbs Up.

    ReplyDelete
  30. Hello again Trish,
    I'm getting back to you regarding the self seeded Silky Oak under Mum's house.
    Two days ago, we uplifted it and transported it in a pot 2.5 hours north and transplanted it into a previously dug hole.
    Not sure if this was the most ideal action, but my thinking was that it is dormant ish now and because it's not really seen sunlight, that it's best to put it straight in the ground as although we have warm, sun lit days, we also have cooler weather for it to adjust in.
    Can you advise me further as to whether I should or could inadvertently over water it, mulch or anything like that to help it along please?
    I've tried to attach some pictures, without success. I can send by other means to help give a better perspective of it's new home if needed.
    The surrounds are dry schlerophyl, it's particular pocket is Northern side, however a line of pine alongside is well grounded . The ground is rock hard, volcanic clay. I have been establishing other natives over time in similar vacinity; Tuckeroo, Firewheel, all very slow growing.
    Thank You Again

    ReplyDelete
  31. Hello Jaime.
    I think you reasoning that this is a good time to move your plant is probably good.
    Plants generally need extra water after transplanting because no matter how careful you are, you are sure to have lost quite a lot of fine little rootlets. It would be hard to over-water a plant like this one.
    It is also worth remembering that this is the time of year that plants do tend to make root growth rather than leaf growth - so yes, help it along. It would also enjoy mulch to keep that ground moisture level even.
    I'd love to see your photos. There is an email address in the right hand column (if you are seeing my blog in the computer view).
    All the best.
    Trish

    ReplyDelete
  32. do silky oaks die from the top down

    ReplyDelete
  33. That's a hard one to answer.
    I imagine silky oaks have a number of ways of dying.
    You don't mention whether you are talking about a seedling, or a venerable old plant.
    Drought can cause a plant to die from the top down.
    At this time of year (assuming you are in Australia, which you haven't told me) your plant might not be dying at all, but simply having its annual leaf-drop. If so, it will be leafing up again very soon as well a giving you a wonderful display of flowers.
    If you'd like to talk about it further, I suggest emailing me (address in column to right, if you are using the desktop view, which can also be accessed on a phone.)
    Trish

    ReplyDelete
  34. Hi Trish, I stumbled across you while researching what to do about a terrible infestation of mistletoe on our lovely old Silky Oak.
    You're only a few hours from us (Toowoomba/Villeneuve) so local.
    I've read that drilling and using 2,4-D or Dichlorophenoxyatetic in non-growing season could be effective.
    Wondering if you have any experience with this issue.
    Thank you, Cheryl

    ReplyDelete
  35. My VERY strong recommendation is that you leave the mistletoes alone! They are plants of very high value to wildlife, and unless your tree is on the decline from old age or root damage (not the mistletoe's fault) then your tree will live for many years, continuing to support a large number of birds and butterflies with its mistletoes. They also have very pretty flowers. Mistletoes have a much shorter lifespan than silky oaks, so you may even see generations of them on your tree.
    I large infestation of mistletoes usually only happens when a tree is on the downhill run towards the end of its life. They are a symptom rather than a cause of a sickly tree. Therefore I would suggest that, if you have the room, you also put in some new little silky oak trees, so that you have them for the future.
    One of the common beliefs about trees seems to be, rather oddly, that they don't die of old age. People who believe this waste a lot of time worrying about what killed their favourite tree, or a lot of money on some rather nasty poisons to kill whatever they believe is causing this "unnatural" death.There is no way of saving the life of a dying tree. However, your old tree (like a typical babyboomer) might have a lot of good years left.
    You might like to read a bit about mistletoes and their value to the environment - and do disregard the "old farmer's tale" that mistletoes kill trees!
    Trish

    ReplyDelete
    Replies
    1. Hi Patricia,
      The above query was mine and have only now seen your reply.
      Thank you.
      You'll be pleased to hear that we have left our old silky oak and the mistletoe to its own devices.
      As the highest tree in the neighbourhood, the birds love it as do our native bees.
      We hope it will be there for quite a few years yet.

      Delete
  36. Hi

    Our fifty year old Silky Oak was struck by lightning and split right down the central trunk and has had to be cut back to the trunk - and will be taken out completely soon. We kept the wood as we have a wood fire, and the mulch, is it OK to use this mulch on the garden, especially as we will lose the shade it provided for most of the afternoon in the South Australian summer.

    ReplyDelete
  37. Hi Collette.
    Yes, it is OK to use silky oak mulch on gardens. The only thing it might do is to suppress the growth of any closely related species - Grevilleas, Banksias, Telopeas, and Macadamia nuts.
    Otherwise it should do an excellent job of helping keep your plant's roots in good condition in the hot weather.
    Trish

    ReplyDelete
    Replies
    1. We just had some of our Grevillea robusta trees trimmed. We mulched the leaves and wood together. Can this mulch be used in a vegetable garden (raised beds)?

      Delete
  38. Hello 😀
    I'm hoping you can help ne with my queries. I recently had a large SilkycOak cut down in myvyard as it had been struck by lightning, with a huge crack in the barrel, making it unsafe. I had 1/3 mulched into chip & want to use as a mulch for a native garden. The rest has been cut into rounds to be used for firewood. The stump ground & the sawdust planned for paths. I've since read that SO contains toxic substances that can cause contact dermatitis. Will using the tree as mulch, for firewood & paths be a possible health hazard for me? Do you have any info on the toxicity & safe uses of the wood? I would love to use all of the tree in my yard so I can make the most of a lovely old tree & see that none goes to waste. Thank you Marina

    ReplyDelete
  39. Hello Marina.
    I may not be the best person to give you advice, as different people vary in sensitivity levels. I am certainly not qualified to pronounce it safe.
    My husband is a woodworker and has often made things from it. He found he gets some contact dermatitis, but it is not severe enough for him to avoid working with the timber.
    It should be safe for mulch and paths once laid, but might would do well to wear clothing that covers you up and a face mask, while actually working with it. You might like to water the paths to help the dust settle, but after that there is unlikely to be any comeback.
    It is not actually a very good firewood. You would have to calculate your own risks there. We use it and have never thought it a problem, even though we drink the rainwater that comes from our roof. We do burn it in a closed stove, so are not breathing the smoke in the house. We don't burn much of it, though, as despite having a number of trees we haven't ever cut one down and used the wood in quantity. It would have been mixed with other wood collected from around our block.
    An alternative use for the rounds could possibly be as stepping stones, seats, etc. They would eventually decay, and meanwhile would have provided habitat and food for those microfauna that are such an important part of the ecology, and provide food for birds.
    Hope this helps.
    Trish

    ReplyDelete
  40. Yes, I am pleased to hear that.
    Old trees are like giant apartment buildings, with large numbers of native species, both plant and animal, depending on them. A lot of these are insects, which are near the bottom of the food chain, so the richness contributed by one old tree like yours is huge. It's a good feeling to be the owner of a tree like that, isn't it?
    Trish

    ReplyDelete
  41. So far as I know, It should be excellent for the purpose.
    the only place where I would hesitate to use it would be under other grevilleas, and even then I might be being overcautious. Silky oaks do suppress grevilleas growing under them, but perhaps this effect comes from the roots?
    Don't forget that fresh mulch uses nitrogen rather heavily in the early stages of decay, so you might like to pop a bit of manure or dynamic lifter under the mulch to give the veges a helping hand.
    Trish

    ReplyDelete
  42. Hi Trish. I planted a silky oak about 15 years ago in Nelson Bay, NSW mid coast, mostly to screen a busy road and what was a beautiful tree filled reserve that was cleared. It is splendid, flowering exuberantly. But is becoming perhaps too tall and directly subject to strong westerly winds, from the cleared land.
    My question is, in order to prevent it being blown over and help it fill out at human height, can I simply saw the top off at a height of about 3m? It is probably 6m tall. The trunk at 3m is about 10-15 cm thick.
    I have very much enjoyed reading your advice
    Regards Kate

    ReplyDelete
  43. Hi Kate.
    I don't know that I can give a good answer to your question.
    I can say that it probably wouldn't kill it, but have no experience to support the opinion! I would suggest that you wait until next year after the leaf-drop, which I think would happen in November or December in your district?
    The best chance of vigorous re-growth would be the time when the tree would normally be putting on its new year's worth of fresh leaves.
    Whether the result would be an attractive tree is something that only time would tell.
    Trish

    ReplyDelete
  44. Hi Tricia,
    I live in Brisbane and have a silky oak in the backyard which is about 20m tall. It has one main trunk which forks at about 2m above the ground and runs parallel to the main trunk. The lowest branches and foliage are about 8m above ground. The main trunk has a large ‘knuckle’ at 5m above ground. It looks swollen, the bark is cracked and is seeping sap. The tree otherwise looks green and healthy. Should I be worried that this ‘knuckle’ is a weak point in this very large tree and that it could crack and fall? Thanks, Kylie

    ReplyDelete
  45. Hi Kylie.
    Sorry for the slow reply.
    Yes, I think it sounds as though your tree has a risk of breaking. I would recommend that your get an arborist in to have a look, and perhaps remove that section of your tree.
    Trish

    ReplyDelete
  46. Good morning. Wondering if you could recommend a good arborist in the Toowoomba area who knows a lot about pruning a very mature silky oak. Need this tree to be respected. Thank you

    ReplyDelete
  47. Hi Karen.
    We were very happy with the job done by a company called DJ, who did sympathetic pruning of an old Eucalyptus for us.
    there are probably others.
    Perhaps other readers can make suggestions?
    Trish

    ReplyDelete
  48. Commenting regarding other species that grow well under Grevillea Robusta. Ours is about 30 to 40 metres tall with a shady, heavily mulched zone about 6 metres in diameter.
    Under it grows some very healthy clumps of clivias. The clivias were not dug into the soil but nestled into the leaf litter with some rocks.
    I have recently also added some bromeliads which are happy so far.

    I also believe that our silky oak contributed to protecting our house from the 2020 bushfires in southern NSW.
    I love it!

    ReplyDelete
  49. Hi - we have four very tall silky oaks in our garden. We have noticed that a couple of them are losing lots (and I mean lots) of leaves all year round. In the 25 years that we have owned our place we haven't seen this until just over 12 months ago. Would love any insight as to why this may be? The leaves are driving me crazy!

    ReplyDelete
  50. Good morning - we are in Toowoomba on a 900sq mtr house block which has 4 very tall old silky oaks. The past 18 months or so they are dropping leaves all year round, lots of leaves! Now one is even dropping green leaves, not old brown ones. Wondering if anyone else experiencing this and why it may be happening? Thank you.

    ReplyDelete
  51. Sorry for the slow reply. I have been away.
    It is a bit difficult to make a helpful comment because not everyone's definition of "lots" of leaves is the same. It is usual "now" (i.e. once a year in spring and early summer) for silky oaks to drop all their leaves, and this means green ones. Then they grow a complete set of fresh new ones as they come into flower. They are doing his earlier than usual this year.
    As for the rest of the year, are there still lots of leaves on the trees? Do the trees look healthy?
    Trish

    ReplyDelete
  52. Hi I have unfortunately had to lop the top off my silky oak as it was causing issues getting out RV into our back your .we have left the trunk that is about 2 mt. high . We are in the south Burnett region of Queensland . I’m hoping the tree will regenerate and sprout from the top of the stump ??
    Thanks

    ReplyDelete
  53. I will be interested to hear the result. You might have killed it, and there is also the risk that if it does regrow it will never make a pretty tree. Sometimes, if an existing tree is a problem, it can be better just to plant another young tree.
    Trish

    ReplyDelete