I don't think there is any advantage in waiting for the sake of waiting before repotting. It's one thing if you're waiting for a more opportune period in the growth cycle to repot, or if you're waiting to let the tree recover from recent stress strain, but if I were to purchase a healthy juniper today, I'd be repotting it at my earliest convenience. A pine, I would wait on until August, when most bonsai practitioners repot them in our neck of the woods.

I think too, that it's not a no-no to move plants into bonsai containers, but most inexperienced growers are in too big of a hurry, moving trees to small containers when they should remain in large containers, or even in the ground to develop some caliper and in most cases, taper through a series of trunk chops. Once you move a plant into a small container, the rate of development is hampered specifically. Bonsai containers are for trees that have already been sufficiently developed & have something of a framework or basic structure, but are in need of refinement.

While you can successfully use the 5:1:1 mix in deeper pots, like nursery cans, for growing material on, the material will develop faster in a soil like the gritty mix that doesn't support perched water. This is especially true of plants like pines & junipers that tolerate wet feet poorly. Everything I'm growing on as future bonsai candidates goes in the gritty mix at the first repot, and I've had excellent results with Foliage-Pro 9-3-6 supplemented with a little ProTeKt 0-0-3.

How much top growth you can remove is very dependent on species, state of vitality, and timing, so there is no one size fits all answer. We aren't restricted in bonsai by the same rules that are applied to trees in the landscape, so the 10 to whatever %s we often see suggested for landscape trees are often very light. It's not at all unusual to see trees completely defoliated in June, or to have a nice fat trunk 2-3" trunk chopped back to a 2" stump in spring with nary a branch or leaf to be found. Again, what you can do or get away with depends on species, state of vitality, and timing, and a better 'feeling' of what's appropriate comes with time or the advice of an experienced practitioner. Joining a club will propel you along the learning curve far faster than you could hope to move on your own.

Conifers are CAPABLE of carrying on a small degree of photosynthesis when soils are not frozen, but they don't need light. What they do need is cold. I over-winter a few plants on the bench outdoors, but most over-winter on tables in the attached garage or on the garage floor. You can also bury the pots in the ground, preferably on the north side of a building out of sun and wind.

There are hundreds of potential species that will tolerate soils that are frozen solid. A copy/paste job from a previous post - forgive me if it seems to stray a little:

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 the whole 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) Another example of this genetic variance is that trees found growing and fruiting well closer to the equator need no chill time, while other trees, derived of genetic stock from a more northerly provenance may need a period of chill to grow with optimum vitality in the subsequent growth period/cycle.

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 could tolerate much 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 perhaps beyond.

and

We know that when trees are exposed to freezing, the finest hair roots - the ones that do the lions share of the work are the first to die. In many woody plants, these roots begin to die as soil temperatures drop below 30-32*. As temperatures drop further, larger and larger roots succumb to killing low temperatures. The point is - that many trees that SURVIVE are left with only the largest roots to support them because much of the rootage has frozen. These trees are slow to respond in the spring because they need to utilize stored energy to regenerate lost rootage before they can move sufficient water and the nutrients dissolved in water to support either growth or the flush of foliage that makes the food that allows the tree to grow (this, in the case of deciduous material).

So, while trees might survive exposure to borderline killing low temperatures unprotected, we KNOW it is better for the tree, especially from an energy management perspective, if we give them protection that ensures actual root temperatures don't drop low enough to kill even the finest roots. For most temperate trees, that means we should strive to keep low root temperatures in the upper 20s at their lowest, and below 42* to keep them from growing until spring when we can get them into good light w/o worrying about frost/freeze.

I think that Juniperus sargentii 'Shimpaku', aka Shimpaku juniper is the queen of junipers. You won't find it at nurseries, but it is worth ordering from mail order nurseries & putting in the ground. I have them growing everywhere (from cuttings) because it's such a beautiful plant and so forgiving - a joy to work with. That said, each of the junipers brings its own attributes and challenges to the table. J procumbens 'nana', aka Japanese garden juniper is probably the most commonly found beginner's tree, and is also pretty forgiving & malleable.

Al

Thank you very much....very informative. So, with all that said, I'll first seek out good subjects. The juniper I'll repot right away, and do some shaping. The scotch pine I'll do some shaping, but hold off on the repot until August. Both will get gritty mix. Now my goal here is to keep a decent root system, so I shouldn't be looking to prune too much of the root system, am I right? Maybe just the taproot?

As for winter, if the trees don't need light, I would be safe with them in the garage, so long as I keep it under 40 degrees? I also have an extra refrigerator in the basement that could be useful if that'd work. The problem with my garage is that it is under the house, so it stays at a decent temperature, and could possibly get above 40 on warmer winter days. I also have a shed, but that would obviously get as cold as what the air temperature gets, which on a brutal winter stretch can dip well below zero. Another thought that crossed my mind is heat cables. I have some leftover self-regulating heat cable for gutters, that I could wrap around the pot and insulate with mulch or something. This perticlar cable regulates output based on the internal dielectric resistance, which changes based on the temperature. I just want to head into winter feeling confident that I don't start spring with dead bonsai trees. Thanks again!

Joe

Because most nursery stock is sold as a specific cultivar/variety it will have been vegetatively propagated and so would have been lacking the seed radicle that develops into a tap root. Your goal, in root pruning, will be to develop a root system that is flat/shallow enough to fit into a bonsai pot, and that will be comprised as entirely as possible of fine roots - the roots that actually do the heavy lifting for the plant. Fat roots serve no purpose in containers other than as transport vessels and for looks ..... if they're exposed. Even fine roots can adequately anchor small trees in small pots. To do this, you'll be focusing on eliminating roots directly under the trunk, heavy roots, and heavy/medium-heavy roots that grow downward.

32-40* for over-wintering is about perfect. If temperatures climb much above 45* for several days, the onset of growth will occur & pretty much trump the plant's resistance to freezing temps, leaving it susceptible to injury from cold. If you're worried about temps being too warm, you might want to consider burying pot & all against the north side of a heated building & mulch, where they'll do just fine of you make sure they don't dry out - toss a little snow on them from time to time if required for the moisture.

Al

So now I have decided that I'll stick with the scotch pine, but instead of a juniper as well, I'll be going with a japanese maple. I assume that for the most part that the same things apply?

Joe

Over-wintering is the same, other than the JM is probably a little more tender than the juniper and pine. Repot timing is different too, with the maple best repotted just as buds move in the spring.

Al

Good new Al, I wandered through a common garden center today after work, and a small juniper caught my eye. It had great shape already, growing crooked from the soil, a good start to an informal upright style, and had a nice nebari. I picked it up, and low and behold, it's a shimpaku juniper. Needless to say, I snatched it up, for $8.99. Still having trouble finding my scotch pine though, but I suppose I have untl August. The pines are tough to get small; all the nursuries have them 3 foot and larger, which seems too tall to adequately shape, and far too expensive. So, I'll be repotting my juniper in gritty mix, and from what I gather I should give it a large pot so it can devlope more roots??

Joe