Question
I'd like to grow a Sky Pencil-jap. Holley in a container.  I live in northern N.J. so have pretty cold winters, -10, rarely -15.  Can I grow this in a container and keep outside through winter?  If so, what size container and how often would I need to repot or cut roots back?

Thank you,
DW

Answer
The main issue with these  evergreens is that they are prone to winter burn, particularly if planted in a windy, or very sunny spot (in winter). Depending  on where you look it up, "Sky Pencil" is listed as hardy in zone 6/7 which would make it marginal in a pot where you are. A good rule of thumb, is to go 1-2 zones lower for potted shrubs and perennials, otherwise expect to go through a protection scheme for them every winter.
One way to protect the roots in winter, is to place the container in a 1/2 whisky barrel or some other large container, and cover up to the edge of the pot with soil. This will insulate the roots, and add weight to keep the plant from being blown over. As the tree gets large enough it can be transplanted into the large container.
Prune in the spring to give the plant extra body and strength. Don't let the plant become stressed and weak.
Give it a balanced fertilizer in the spring, and plenty of water, and sun, all summer. The healthier the plant, the better it will withstand the elements.
To avoid winter-burn, I highly recommend that you buy some Wilt-Pruf, and apply according to directions once around Nov./Dec. and again around Jan./Feb. if the weather conditions are suitable according to the label.
The best protection would be to move the container to a garage or basement when the temperature drops to dangerous lows. The advantage to having the tree in a container is that is will fit on a hand truck and move to safety.
Check the roots to see if they are becoming too large for the container. Don't wait until they have moved out of the soil on the bottom of the pot. Only move to one size larger when potting up. This is because, if the container is too big, the water will be pulled to the sides of the container, and the roots in the center will be dry. In the smaller container, the water is directed to the roots. If the container is too small, the roots fill up the area, and the nutrients and water can not penetrate the mass.
Do not cut the roots, unless you have too. Gently loosen them, so that they will leave the confinement they are molded into, and go out into the new soil, in the new container.
Water enough to fill the soil in the container with moisture. Then, let the soil dry enough to let the oxygen back into the top inch or two of soil. Water replaces the oxygen. The tree needs oxygen to grow. Without it, the tree will drown from too much water.
I don't recommend covering the plant to protect it. This often causes more damage, then good.