Bonsai for Beginners – Part 8 – Pests, Pets, Partners & Posterity

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There is yet another thing that I feel needs addressing before I dive fully into describing individual taxa and how to care for them, and that thing being the beings that might share your household with you and your trees.

Let’s start with a sad anecdote about partners. I don’t have a partner, but my older brother is married. And when I started expanding my bonsai collection and some of my trees started to look really impressive, he wanted to try it too. I have him one really good indoor bonsai, Cupressus californica and one mediocre but with good potential Ficus benjamina. The trees prospered for a while and looked good, but my sister in law shuffled them around the house to places where they “look good” until she shuffled them on top of the cupboard above the kitchen counter. When I have seen this on my visit, I warned them that the trees won’t survive that, because they need a lot of sunlight in vegetation. It is possible to display trees in a hallway or some other place for a while to decorate your home, but ultimately they are living beings and their needs must be met. My sister in law made appreciative noises and pretended to care, but she only shuffled the trees into places where they were even worse off. Until they died, as I predicted.

I have begun to suspect ill intent, but I could not prove anything and I could not say anything even if I had proof. My brother was determined to have bonsai trees, he bought some, he even successfully poached some from the forest against my advice, and I bought him a healthy Pinus pentaphylla, the most iconic Japanese bonsai species, and I chose a tree with really great potential. The trees seemed to prosper for a while, and then they suddenly all died and my brother lost all enthusiasm at all that labor wasted.

For a long time – until last year, in fact – I thought he has just been unlucky. Trees die, it happens to me all the time. But recently I learned that he was a victim of a concentrated effort of his wife’s family. His father in law got bitter after he split with his mother in law, he got drunk and he babbled out what really happened to someone and it came in a roundabout way to me. They deliberately sabotaged all my brothers’ hobbies and I was deemed as persona-non-grata in the household. Their family deemed all hobbies as a waste of time, only activities that make money or are work around the house were allowed. And I came in there with my perfidious influences on my brother and their grandchildren like reading books and growing useless trees in a pot and reminding my brother of his own hobbies like making models and playing chess.

The high-end trees that I gave my brother were indeed deliberately shuffled off into places where they withered and died, under the pretense of appreciation. And when they could not do that with the outdoor trees because my brother put his foot down and claimed a piece of garden for his hobby and told them to back off, they have secretly put dish detergent into the barrel he used to collect rainwater for his trees. To my knowledge, my brother still does not know this and I won’t tell him. He is happily married. But I can’t stand his wife and his mother in law.

So before you start growing bonsai trees, make sure that people who share your household are OK with it. Do not just assume they are.

I also do not have children. And I do not currently have any pets, but I used to. For both children and pets apply the same rules as for any garden- or potted plants. Make sure that anything poisonous is out of their reach so they cannot nibble at it. Or better yet, make sure they cannot nibble at any plants at all. If you are cat-owned, you will have to make extra sure your owner does not knock any pots off the shelves to teach you a lesson.

Some plants are more poisonous to birds than they are to mammals, so if you have parrots and let them out of their cages, you too need to be extra careful. For outdoor bonsai, this does not seem to be a problem. Local birds never nibble on local flora if said flora is inedible or poisonous, and I never had them nibble on small trees when big ones are nearby either. And I have never seen local birds try eating indoor plants when I put them outside. Indeed having a bird feeder near bonsai trees has even helped a bit with pests because the birds do like to sit in the trees and they pick off any wintering eggs and pupae they find while there – especially tits are helpful in this regard.

The almost inevitable companion in your household once you start to grow any kind of plant are pest insects.

Worst of these are scale insects. They tend to attack mostly evergreen plants with hard leathery leaves, like Laurus, Ficus, Citrus, and Myrtus and once these fuckers get a foothold, it is really difficult to get rid of them. I have managed to finally destroy them by a combination of mechanical removal with concentrated water spray from a small nozzle- that allows for mechanical removal from even the least accessible nooks and crannies -but the spray must not be so strong so it would poke holes in the leaves. What also helps is to wash leaves and stalks with a cloth soaked in rubbing alcohol or cheap vodka, to destroy the eggs. Sometimes even more drastic measures are necessary, like severe pruning of the tree and trimming of all leaves. Insecticides are usually useless, they do not penetrate the hard shells very well.

Wooly aphids are similarly persistent and obnoxious and similarly difficult to get rid of. Here I did not in fact succeed and I am battling with them for years now on one pine. The problem with these is they tend to attack conifers like Pinus, Picea, and Larix and they nest themselves into the nooks and crannies around the needles, twigs and in the bark recesses, where they cannot be reached at all. Some even attack roots and those are usually a death sentence. I used to keep them at bay with a timely spray of daisy extract with a drop of detergent, but daisies disappeared around here for whatever reason and since then I am only left with washing them off mechanically either with water spray or with a toothbrush. I might need to try a commercial insecticide.

Aphids can also be a problem. Birds and spiders do help with their management however, and they are much more susceptible to insecticides and even ordinary mechanical removal than the previous two. They tend to attack mostly soft, freshly growing stalks and leaves of Hibiscus, Tilia, Acer, and others with similar growth patterns (probably my new persimmon would be susceptible too by the looks of it).

Since these pests prefer different plants, mixing the species on your windowsill/bench etc. does help to prevent their spread. Yes indeed, social distancing works for trees too.

Ants are not a pest in and of themselves, but they can spread all three above mentioned pests around your collection outdoors if they are present, because all three produce honeydew and ants love them.

Spiders in a bonsai tree are desired and should not be disturbed if possible. I am sure there are some people who would like to know this.

Fungal (and bacterial) diseases come in many varieties and are mostly species-specific. You must make your own research should you encounter one. Some species are more prone to them than others. The best help is prevention and fungicidal spray. If a tree catches a fungal disease that attacks wood it is usually the end of it. You might try cutting away the whole infected branch and burning it – you might catch it in time and save the tree, but most likely it will get damage that takes years to heal, even if it survives. Fungal diseases that attack leaves /needles are less threatening and can be mitigated by the removal of old fallen leaves/needles in the fall, but not always. Even these mild fungal diseases are detrimental to the tree so they should be avoided.

On the other hand, mycorrhizal fungi are desired. Even a bonsai tree starts to prosper and grow better if it manages to get mycorrhizal fungus on its roots, the effect this has on for example oaks is remarkable- I have observed nearly double growth rate in trees with fungus against those without it, but I did not conduct a proper scientific experiment, so you only have my word for it.

Lichens on roots, branches, and bark are also desired, they add the illusion of old age. They are also an indicator of health and proper care because they grow very slowly and are finicky.

Therefore any application of fungicidal sprays on bonsai trees must be done with care and deliberation and in a targeted manner and not in a “spray and pray” fashion.

One pest that I have not seen mentioned in any of my bonsaist literature are water voles. They do not get to the trees on benches, but if you take them off the benches for wintering during a tough winter, they can get in and wreak total havoc. In 2011 I have lost this way several prime trees and many others were damaged to such an extent they still did not recover. Voles also destroy a significant portion of any trees that I plant in my garden, I was unable to replace my cherry tree due to them and I have to plant new trees in my coppice two-three times before they survive long enough to be vole-proof. Having a cat helps, although they do not like to eat voles too much. But they do kill them and scare them off. The problem in my garden was also less severe when we had a dog, And it was nearly non-existent when an owl was nesting in a nearby spruce tree. However the 2011 disaster has happened when we had two outdoor cats and a dog, but the voles were safe under half a meter of snow. Voles are a mortal enemy to me. Forget capture and release traps. You can either be on the side of the trees or on the side of the rodents, not both. So killing traps, regularly checked and put safely with proper bait in order to not catch shrews or birds by accident, it is.

And lastly – it should go without saying that if your tree is visibly infected or infested, you should not display it. Especially not in an exhibition where it could infect other trees. Visible infection or infestation is an instant disqualifying criterion in competitions, and rightly so. As a beginner, look for any of these when buying a tree and do not take any that is visibly ill. You do not want to carry these unwanted guests into your household.


  1. kestrel says

    The idea of someone deliberately killing trees in order to hurt someone else is really disturbing. I’ve met people like that; but it is still hard to understand why someone would do that.

    I’ve had a problem with spider mites before. I’ve tried to grow roses (the miniatures) in the house and they always get killed by spider mites. It is sometimes daunting to grow things indoors.

  2. says

    @kestrel. spider mites are a scourge too, now that you mention it. I currently do not have too big problems with them, because I have relatively high indoor humidity (50-60%) all year round, so I forgot to mention them.

    What helps against spider mites is to give the afflicted plant a cold (but not too cold) shower as soon as you notice them. Spider mites are very susceptible to humidity and usually, they do not survive more than a few such showers. If the plant reacts poorly to having too wet roots or cold water on roots, you can protect them with a plastic bag during the shower. I have taken to showering my trees a few times a year as a matter of course. I occasionally spot a spider mite here and there, but I haven’t had a serious infestation in years.

  3. Jazzlet says

    Scale insects are difficult to get rid of, but doing so at the right time of year helps, and sprng is the right time to be looking out for them and removing them before they have a chance to harden the protective scale. For wooly aphids the est method I have found is a small stiff-ish paintbrush. The brush I use was cheap, rubbish for painting pictures, but with around 2mm of bristles it can get into most of the nooks and crannies wooly aphids like and mash them up without damaging the plants.

    The things I find absolutely impossible to get rid of are root aphids, I made the hard decision to get rid of my streptocarpus collection this winter as they were all infected. You can’t see root aphids for the obvious reason they are on the roots, by the time they become visible you have a sizeable colony and the little bastards are spreading to any nearby plants. At least replacing the streptocarpus isn’t hugely expensive if I start small, but it still hurts.

  4. lumipuna says

    So … How much dish soap does it take to make irrigation water toxic to plants? Does it make the water visibly foamy or slicky?

    I guess being a hater of horticulture is kind of self-defeating, if you end up never learning about herbicides.

  5. kestrel says

    @Charly: Aha! Thank you! Yes, the indoor humidity here is about 16%. This gives me hope I can get a miniature rose growing in the house again.

  6. says

    @lumipuna, in fact, using the dish detergent was pretty clever. It has an advantage over a herbicide in that it can only affect the plants over a longer period of time, they wither slowly and some sooner than others and not all suddenly at once. And it won’t affect grass or any plants freely in-ground, because it gets diluted fast enough. It is only dangerous to potted plants. I, of course, do not have extensive experience in this, but this was why I did not suspect any foul play for years and I would never know about this if one of the guilty people did not talk about it.

    When I was living in a university dorm, I had two bonsai trees with me there. One of my roommates threatened me once with pouring dish detergent in the pots, only half-jokingly. So there are people out there who know that dish detergent is harmful to potted plants and they are not horticulture experts either.

  7. lumipuna says

    Ah, now I realize the dish soap thing was specifically about potted outdoor plants. I can see how they’d be much more sensitive to long-term low-level exposure.

    My previous comment was somewhat snarky, but in honesty I have no idea how toxic exactly dish soap is for plants.

  8. says

    Your brother’s in-laws would get along perfectly with my mum 10 years ago. There’s approved activities* and everything else is verboten. I’m not excusing your sister in law, I’m just wondering how much fun she had (at least) figuratively beaten out of her over the years. Deliberately destroying the trees is emotional abuse imo.
    Though I did not know the thing about detergent, because kali soap is one of my top notch anti pest sprays…

    *She did allow for hobbies, but only hobbies she approved of. Only that I never learned knitting.

  9. says

    @Giliell, I am with you on the emotional abuse bit. Allegedly the destruction of outdoor trees was something that only my sister-in-laws’ parents planned and she personally was not part of it. I have refreshed my memory (= I asked my mum) and the father in law told it actually directly to my mother. My sister in law has improved as a person in last years and she started to realize some of the things you have said, but that is another story for, perhaps, another time.

    A little bit of dish detergent added to water with insecticide does help it to penetrate the water-repellent protective coat of wooly aphids, and it is not harmful to the “above the ground” plant parts. I have mentioned a spray made from dish detergent (circa a teaspoon), shredded daisies (about ten stalks) and water (about half a liter). It is a cheap, easily made insecticide that works really well.

    And as Paracelsus has said, the dose makes the poison, and that goes for dish detergent in water too.

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