A couple helpful hints:
1) Keep the dirt that was in the flower boxes in the summer. (Do not empty the container and replace with new soil). The reason for this is that the root base (which was established in the summer by the flowers) provides support for the spruce tops and other greens. When you place the greens in they will stay more stable and will be less likely to fall out.
2) Make sure you water the greens in. This is for two reasons really. The first, is to supply water to the greens and keep them from drying out and turning brown. The second, is when the dirt is wet and we have the inevitable freeze the greens will stay in tightly.
3) Use things you find! It's amazing the things you can find just by taking a walk in the woods! Make this a fun kid activity by telling them they are going "foraging"! Chances are the kids won't know what the word means until its too late, lol!
4) Lastly, enjoy! You can always add the holiday color later. The most important thing is to get the greens in early enough so they freeze in.
Smaller window box!