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To give a little bit of context, I'm looking to start growing bonsai trees indoor. I really like maple trees and I'm thinking of building an indoor growth enclosure(like a Grow Box) with artificial lighting(for those interested I'll be using driverless full spectrum grow LEDs), temperature control, etc. I know these plants require dormancy, and to avoid "eternal summer", which is fatal, some people use refrigerators to meet dormancy requirement. Guess it depends a lot on the type of maple tree, but my questions are the following :

  • What's the maximum temperature to meet dormancy requirements and "simulate" winter?
  • How should I vary the light cycles during the year?
  • What humidity percentage should I be working with?
  • How should I vary the light cycles and temperature during the year?
  • If you are just beginning for Bonsai, I heartily recommend taking classes in the flesh? Not just by internet. All of your questions totally depend on the species of tree, plant you decide upon. Note: Bonsai is about miniaturization. A healthy looking tree that should not be healthy at all. If you've ever done any model making, it is fine textures, tiny leaves that do best as Bonsai. Maple trees have large leaves. Azalea on the other hand is diminutive sized leaves. You want to make a tiny tree from a tree with genetically large minded genes. – stormy Jul 27 '18 at 6:02
  • Thanks for the recommendation, that's exactly what I was planning on doing! – Mr. Branch Aug 1 '18 at 11:23
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    Lucky you! Bonsai classes are to die for...seriously. I took mine from guys that don't speaky english! And I understood. Your classmates will also be a great networking tool. Anyone taking bonsai classes has to be of a like feather and cool. – stormy Aug 1 '18 at 19:57
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The standard dormancy temperature in research is below 40F/5C. Many species then have a bud chilling requirement, an accumulated number of hours below 40F/5C, before dormancy can be broken. I think acer palmatum/shirasawanum/japonicum do as well, but I don't know what the hours are. Acer palmatum/shirasawanum seeds require something like 6 weeks or 1000 hours below 40F/5C to germinate. It would seem sensible to expect the bud chill requirement requirement to be similar, even though this need not be the case.

All temperate trees switch their growth mode with the passage of the summer solstice. Before the solstice, cambium cell division rates accelerate and shortly thereafter decline, ultimately ceasing when temperatures drop enough to affect dormancy. In my climate, acers are in the accelerating cambium cell division mode for 5 months, at most. The safe thing to do would be to emulate mother nature with, say, 6 months of 18 hours days and 6 months of 8 hour days with a 6 week period of cold, but it is an interesting question: how do maples behave with long days and low temperature, for example. Of course, if the tree is leafless it likely doesn't matter what the day length is.

I guess that you want humidity in the range 50% <= rH <= 80%. Fungal problems are synonymous with high humidity and still air. I am guessing that keeping it below 80% will prevent this (you could spray periodically with a solution of 2 tablespoons 3% hydrogen peroxide from the grocery/pharmacy in a quart of water to address fungal issues that arise). The rH in my location rarely falls below 50% and these species thrive. It does occasionally dip to as low as 20% for short periods without causing any ill effects. The combined effects of full sun (OM: 100k lumen/m^2)and mild winds/breezes do cause leaf damage, but it is hard for me to conceive of how this would occur indoors.

EDIT: IMHO, 3% peroxide could be used to sterilize the grow box from time to time to limit the possibility of fungal problems. Perhaps it is advisable to sterilize the grow box before introducing the maple. The diluted spray I suggested could be applied to the entire tree and as a soil drench prior to introducing the maple to the grow box.

  • Interesting the use of H2O2. I have to think about this one. The one and only way other than a humidifier is to use a flat tray of pebbles with water to increase humidity. In doors would be the only place I would increase humidity. Spraying with water does nothing for humidity. Nice to clean dust but I take my indoor plants into the shower once a month during the winter, in summer they are on a covered porch and get hosed off. Bonsai, gently. Very nice on the dormancy daylight hours. Does this really put them in dormancy to abscise leaves? A fan is critical and cheap. – stormy Jul 27 '18 at 21:54
  • Possibly you misunderstand my comment wrt peroxide, @stormy. I am only suggesting that it is an effective anti-fungal foliar spray. Separately, high humidity and still air is a potent recipe for fungal infection. – Jim Young Jul 27 '18 at 22:42
  • In my experience, antifungals or fungicide are considered 'raincoats'...one drop of water holding one tiny tiny spore landing on actively photosynthesizing plant material will infect the entire plant. There are no remedies. The only fungus I know that one can treat after the fact is Powdery Mildew. Fans and blowing air, pruning excess non necessary foliage and never watering in the evenings...best practice. I found spraying milk and water (1:9 ratio) is amazingly effective for powdery mildew! Bamboo gave me this formula and it works... – stormy Jul 28 '18 at 1:09
  • I am not sure at all about the efficacy of H2O2 sprayed on plant material for anti fungal properties. I've read about the H2O2 being used in soil...preplanting. I am not impressed. For one thing H2O2 is not specific. There are important fungus species you WANT to be in your soil. Rain coats mean not allowing one spore in one drop of water to contact photosynthesizing plant material. Kind of tough to moderate. Rain coats also mean covering the soil so that it won't be splashed up on the plant. Too bad many fungi spores are floating around in the air as well as the soil. – stormy Jul 28 '18 at 1:16
  • Antifungals such as Daconyl, copper sulfate, work by leaving a residue which, if not washed away by rain nix pores that may falls on the leaf. This also means they can accumulate 'environmentally. Hydrogen peroxide is a long-known and well-known disinfectant. It releases reactive oxygen and becomes just water; so has no possible residual accumulation/toxicity. No foliar spray applied anti-fungal is going to do anything about the infected interior tissues - SOP = remove affected leaves (spore sources) and spray ... until no more leaves affected. – Jim Young Jul 28 '18 at 1:44

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