Always keep cut trunk of the tree submerged in water. If it has been out of the water for more than a few hours the sap will run and form a seal on the bottom of the trunk and it will no longer be able to take in water.
Additives are not necessary and fresh water is best for the tree. Over the years, we've heard it all, from sugar, to miracle grow, to Sprite or Coke, to aspirin, to the liquid in liquid Advil, and even to bleach. We always tell our customers that plain fresh water is best, and that's what we personally use.
Very Important, is to use HOT tap water the first time you are filling up your tree stand. As hot as it can get out of the tap. This will melt any sap that may have formed on the cut of the trunk and will allow the tree to drink up the water more easily. After the initial watering, temperature is not important.
A large tree can absorb a couple of quarts of water per day. So check your water level daily, regardless of the size tree you have. Try to use a tree stand with a large water reservoir.
Once you get your tree home, if it has out of water for more than a few hours we suggest making a fresh cut on the trunk. About one inch is sufficient.
You may leave the tree outside (in a sheltered area such as a garage or shed is preferable). Place the tree in a bucket of hot water. When keeping a tree outside, make sure the water does not freeze.
If possible, select a location inside your home that is not too close to a fireplace, wood burning stove, heat duct, or radiator.
Place the tree in the stand with the netting still on. This makes it easier to move and straighten the tree. Netting should be removed once the tree is secure and straight.
The tree will take a couple of hours to return to its natural shape, once the netting is removed.
Always keep the bottom of the trunk of the tree submerged in water as long as it's inside your home and it will stay fresh for weeks!
Barclay's Christmas Tree Farm