The length of time that a fresh cut tree can last indoors is dependent upon when the tree was cut, the species of tree, how the tree was transported, where the tree is sited within the house and the care of the tree after it has been brought in. Trees that are not fresh and not given adequate moisture may last only a few days. Trees properly cared for can last up to 8 weeks or more.
The single most important factor in keeping a cut tree fresh and healthy is to ensure that it receives adequate amounts of water. A proper stand to accommodate the tree and serve as the water reservoir should have a volume equivalent to at least 1 quart per inch of trunk diameter. If the tree has a diameter of less than 4 inches, the stand should still be able to hold up to 1 gallon of water, as a healthy cut tree can imbibe this much per day initially.
Place your cut tree as far away from a direct heat source as possible to extend its indoor life span. Avoid obvious places such as near fireplaces, air ducts, vents and radiators. Placing a cut tree near a television, near frequently burned candles or even in a south facing window can speed up the decline of a fresh cut tree indoors.
Preventative measures are the first steps to keeping your fresh cut tree indoors for as long as possible. Make sure during transport from the store or field that the tree is covered, as it can lose moisture when it makes the trip on the top of a vehicle or in the back of an open-bed truck. If your tree is going to be outside for more than an hour after being cut, make sure to give it a fresh cut prior to bringing it into the house to help it to absorb water once inside.
A tree that is still attached to its roots in the field before bringing it home will last considerably longer inside than one that has been already cut for weeks. If cutting your own tree is not practical, make sure to test for freshness on prospective trees by gently pulling on a branch to see if green needles come off. If more than a couple fall off, the tree is likely not fresh and will not absorb water easily. If you give the tree a shake and several brown needles fall out, that is normal and not a sign of dryness.