Let's take a moment here to discuss "buds" on a JBP. There are three primary types of buds on a JBP: Spring buds, adventitious buds, and needle buds.
Spring buds are the ones that are growing vigorously right now, and every tip end of the tree has one, and they grow straight up, and can be very long. Left to it's own devices, these are the buds the tree wants to grow to be strong, tall, and vigorous. Unfortunately, these candles are generally TOO strong for our purposes. There is a section on these candles have no buds of any kind. This is the section between where the candle emerges from last year's growth, to the first needle. This section can vary in length, but is usually at least about an inch, to as much as 6 inches! Waaaay to long.
Down at the base of the spring buds are the "adventitious" buds. The hormones produced by the growing Spring bud supresses these from developing, usually. Sometimes you get multiple Spring buds from one spot, and even if you do, there are still dormant adventitious buds there. These are the buds that the tree's damage control. If something happens to the spring bud, the hormone flow that suppresses the adventitious buds will stop. Which allows the adventitious buds to start to grow. There's usually 3 to 5 buds at the base of each Spring bud. When we decandle, these buds are the ones that will grow. When they do, they will have less energy since the Spring bud used so much, and the energy is spread between 3 to 5 buds, rather than just one. What this does for us is the "neck", the space between where the bud emerges from last year's wood and the first candle is much shorter. A quarter inch, maybe. They won't extend as far, and depending upon when the decandling is performed, these needles will have a shorter growing season, so they'll be shorter than those the Spring candle would produce.
Finally, we have "needle" buds. There is a bud between each needle in a pair of needles. These are very weak, and if they grow, they form unusual stems. They will eventually develop to be indistinguishable from regular candles in time. These are the tree's defense of last resort. If a branch breaks off behind the spot where the adventitious buds are, but there are still needles, the branch might develop needle buds. They're unreliable, though. Typically, if you get a needle bud growing, and it happens to be in a good place, use it. Just don't design your branch around the idea that you will stimulate a needle bud.
Ok. There they are.
What then is "back budding"? Generally speaking, when we talk about "back budding" on JBP, we are talking about getting a bud to pop from old grey wood where no greenery exists. Remember the hormones that suppresses the adventitious buds? Well, those adventitious buds might get suppressed for several years, but they are still there. If something happens, like a decandling, or pruning that interrupts the auxin flow suppressing them, they might just pop out and develop. They will be very weak. Maybe only producing a couple pairs of needles. Leave them alone for a couple years, until they get strong enough, and then you can decandle them. In fact, you might be able to eventually cut back to them. We call this process "chasing the branch back to the trunk". Back budding generally doesn't happen once true bark forms. The bark shades the buds from the sun. So, you need to try to expose the smooth grey branches to the sun, if you want back budding. This is where wiring helps. When you wire, then bend the branches down, it opens up the branch structure to the sun, allowing sunlight to hit the wood, thus stimulating back budding. What kind of bud will be stimulated? Most likely an old adventitious bud, but you can get old needle buds, too.
To recap, when we decandle, we are not "back budding". Decandling stimulates the adventitious buds. I tend to get more "backbudding" over the winter, with growth (needles emerging) in spring. That's because I reduce the second flush of adventious buds on each twig to two in the fall, and wire in the fall. The drop in auxin from 5 buds to 2, and exposure to sunlight stimulates old dormant buds (back buds).
As to when to decandle, every person develops their own schedule for trial and error. Every growing season is different, so it's an art, not a science. Generally speaking, if you want longer needles, decandle early. If you want shorter needles, decandle later in the summer.
