Tree limbs traced in lights are beautiful but do not let the tree go into spring with cords still wrapped there. That can girdle an expanding limb in just one season.
A tree or shrub limb expands in diameter as it adds a new layer of wood each year. No matter how old or large it is, if that expansion runs into a girdle -- any encirclement from a hammock noose to a holiday light cord -- the delicate and irreplaceable living layer under the bark can be killed. Sometimes death comes in one year, other times the girdle has enough give or the branch a slow growth rate so death takes longer.
In this case the strand of lights remained on the tree through a whole growing season. During that 9 months it's become so tight the bark's bulging around it. The limb can still be saved if the girdle's removed right now. However, if the cord's still there next spring, everything above the lowest girdling loop will die.
It's so easy to forget about lights as the New Year ages. Many people realize their mistake only in summer when they notice a dead or dying portion of a tree's crown.
So act now. Go out on that first fine, above-freezing day and unwrap your trees. If you can't unwrap, clip the cords. On the one hand it's a $20 string of lights -- on the other, a limb or a tree that took 20 years to grow.
We covered this and other pursuits for productively channeling winter gardening energy in What's Coming Up 67.