First off, the hardiest palms are the ones that come up from seed onsite and grow up in place. But we are impatient, we want faster results, so we plant nursery grown plants which many times are not as hardy because they have been pushed into faster growth. Perfect example is Windmill Palm. Their new emerging spears are tender the first two to three years in the ground when grown from containers and benefit from properly wrapping. Use frost cloth during late December through late March especially when temperatures are expected to go below 12 degrees especially for long periods. When they are established and mature they can take temperatures down to around 5 degrees before leaf damage occurs. Young palms are not as cold hardy so why take a chance. The protection is not needed in many Winters but is there if needed.
Another very important thing is to not keep the soil too wet during the Winter. I also don't recommend soil amendments that many times keeps the soil too wet. The palm has to eventually grow in the soil you have so don't tease it with amendments in the planting hole. If you have wet, clay soil for instance don't think that adding sand and/or rock to your backfill or in the bottom of the hole will help the drainage as both are more porous than the soil and water will collect there creating a "bathtub effect". If it is too wet plant on a raised bed or mound.
Do not fertilize late in the year especially with long term slow release as that will keep them fast growing and with tender buds during cold weather resulting many times in damage. Palms do not go dormant like many other plants but they need to be allowed to slow down since they can somewhat continue growing in the Winter.
These are recommendations based on growing palms both personally and commercially here in Eastern NC for the past forty some years. These recommendations may or may not apply to other areas. If you have planted palms and had success by other techniques by all means continue to do so.
Always ask the nursery you purchased the palm from for directions if you are not sure how to plant and take care of their palms.
Winter Protection for Young 3, 7 and 15 gal Palms for the