Northern White Cedar - All Questions

Young trees with thin bark can be susceptible to bark splitting. Usually not fatal, the open area can allow for ease of entry by disease organisms. This can cause decay. Avoid fertilizing trees late in the growing season. Frost cracks may occur during late winter/early spring when temperatures fluctuate dramatically. Cold nighttime temps. may cause the water inside the trunk to freeze and therefore split the bark. Another cause may be excessive or vigorous growth during a wet season which is following dry weather. Yet another cause may be sunscald, which may be lessened by avoiding heavy pruning in trees with dense canopies. It is better to to thin the limbs gradually, over a period of several years. Here is a link to a pertinent information page from the MSU Extension. https://m9b4k7g3.rocketcdn.me/wp-content/uploads/2017/01/BarkSplittingMSU.pdf

Yes dear will enjoy the young seedlings very much. There are a few different choices as to how to protect the seedlings until they get established. You can cage them in some manner either use hardware cloth, chicken wire or fencing of some sort, or you can use a deer repellent product.