i would suggest against startin aproject like that in mid summer. the best time to start anything like that is spring that way your tree has the best possible opportunity to adapt before winter. however if your season change this year is similar to ours here in the states i would say you have a chance. it is your plant though and if you want to try it best of luck to you.

I would keep things pretty cold (28-30 degrees F) for a while longer, if I were you. With the heater and shelter, you're forcing the maples to bud a bit too early. Before you know it, you will be dealing with fully leafed out maples when there is stil alot of danger from hard freezes still around. I would keep things cold to keep the trees from leafing out until at least the end of March. You want as little danger of frosts and freezes as possible when Japanese maples start to leaf out--even if you have heated porch. When the plants leaf out, they need sunlight. You will get alot of long weak growth in such conditions that won't help bonsai training along very much.

I successfully tend to some 200 containerized trees that are in various stages of development for bonsai, many are Acers. I lecture regularly by invitation on container culture in general, and many other tree-related subjects. My next presentation is Wed, May 6, to the Gladwin County, MI Master Gardeners. The above-ground portion of trees are able to tolerate much colder temperatures than roots. 14* is considered the industry standard for killing low for mature rootage on A palmatum, so it's inaccurate to say that roots are fine above 15* soil temps and in jeopardy at temperatures below 15*. Succulent rootage and hair roots are often unable to tolerate temperatures only slightly below freezing. As temperatures fall, larger and more lignified roots succumb to the cold. As stated above - all roots on a plant are not created equal when it comes to cold tolerance. 12-24 inch (deep) soil temperatures rarely see temperatures drop much below 25*, but the top 6" of soil, where the bulk of our containerized tree's roots are - does get extremely cold - certainly well below killing lows for fine rootage (though perhaps not for larger roots). I could site Dr. Whitcomb for support, but I'll let you look at his text at your leisure, since it appears you have it. Note Chapter 13, pages 308 -338 to see that what I'm saying is not only logical, but it's supported abundantly in his work as well as a plethora of other literature. Something I wrote previously: "Commonly, each species of plant has a general range of cold-hardiness. Within species and cultivar, cold-hardiness is genetically determined. That is to say that a plant that is propagated from cuttings or tissue culture will have the same ability to resist cold as the parent plant. Plants cannot "develop" a greater degree of cold-hardiness by repeated or prolonged exposure to cold, even after 100 years (trees). If we pick any plant at random, it may or may not be able to withstand freezing temperatures. The determining factor is the plants ability to prevent freezing of bound water. Bound water is the water inside of cells. There are actually three kinds of water to consider when we discuss "freezing". The water held in soil - When this water freezes, and it can freeze the soil mass solid, it doesn't necessarily kill the plant or tissues. Then there is free or unbound water, also called inter-cellular water. This is water that is found in plant tissues, but is outside of living cells cells. This water can also freeze solid and not kill the plant. The final type of water is bound water or intra-cellular water. If temperatures drop low enough to freeze this water, the cell/tissue/plant dies. This is the freeze damage that kills plants. Fortunately, nature has an antifreeze. Even though temperatures drop well below freezing, all plants don't die. In hardy plants, physiological changes occur as temperatures drop. The plant moves solutes (sugars, salts, starches) into cells and moves water out of cells to inter-cellular spaces in tissues. These solutes act as antifreeze, allowing water in cells to remain liquid to sometimes extremely low temperatures. The above is a description of super-cooling in plants. Some plants even take advantage of another process to withstand very low temps called intra-cellular dehydration. The roots of your trees can stay frozen for extended periods or go through multiple freeze/thaw cycles w/o damage, so long as the temperature does not fall below that required to freeze intra-cellular water. If roots remain frozen, but temperatures remain above killing lows, dessication is the primary concern. If the tree is able to take up water, but temperatures are too low for the tree to grow and make food, stored energy becomes the critical issue. Dormant and quiescent trees are still using energy from their reserves (like a drain on a battery). If those reserves are depleted before the tree can produce photosynthesizing mass, the organism dies. There are a number of factors that have some affect on the cold-hardiness of individual plants, some of which are length of exposure to seasonal cold, water availability (drought stressed plants are more cold tolerant), how recently planted/repotted, etc No one can give a definitive answer that even comes close to accurately assessing the temperature at which bound water will freeze that covers an entire genus, or even species. Unbound water is of little concern & will usually freeze somewhere around 28*. Some material will be able to withstand little cold & roots could freeze/die at (actual) root temperatures as warm as 25-27*. Other plants may tolerate much colder actual root temperatures - as low as 10*. There's just no way of knowing unless you have a feeling for how cold-tolerant the genetic material the plant was derived from might be, and finding out is expensive (from the plant's perspective). ;o) It's wise to remember that root death isn't instantaneous at one particular temperature. Roots succumb to cold over a range of chill with cultural conditions affecting the process. The finest roots will die first, and the slightly thicker and more lignified roots will follow, with the last of the roots to succumb being the more perennial and thickest roots. Since any root death is a setback from an energy allocation perspective, and root regeneration takes valuable time, it's probably best to keep actual root temperatures in the 25-40* range as long as we can when the tree is resting, even though the organism as a whole might be able to tolerate lower temperatures. Even well established trees become very much like cuttings if all but the roots essential to keep the tree viable are lost to cold. Regeneration of roots is an expensive energy outlay and causes the trees to leaf out later than they normally would and shortens the natural growth period and reduces the potential increase in biomass for the next growth cycle and beyond." Summary of what I originally put forth: If you repot in fall, you should protect roots against freezing temperatures or you will lose a portion of the roots. It is an expensive outlay from an energy allotment perspective for the tree to have to regrow these lost roots. The energy that goes into regeneration of roots lost to cold could/would have been used by the tree for foliage production and branch extension. Winter-killed roots represent a loss in potential biomass increases and it makes no sense to adhere to a practice that doesn't take cold-damage into consideration - unless you wish to use it as a tool to slow trees down. Al

I have repotted my new aka shidare momiji about 3 weeks ago or so, and infact 2 times in one week as I was given wrong advice on soil and the glazed pot I used got rather hot under the sun. in fact the last move to its current container, I had to wash away most of the soil on the roots as the soil would have been quite different from the new mix and caused problems. now its in a large terra cotta pot with good draining mix soil. I'm pretty new to this, so I guess I would not advocate what I have done, but seems like after 2 weeks in shade the tree is back to its health and budding new leaves well. some pictures I took yesterday and today.. Here is a link that might be useful: my new aka shidare momiji