The best time to buy a Christmas tree from Lowe's is usually around mid-December, when they start to discount their trees. This is also the time when most people start decorating their homes for the holidays, so you can expect to find some great deals on trees and other holiday decor items at this time. However, it's always a good idea to keep an eye on the store's sales and promotions, as they may occasionally run special discounts throughout the season.