This is the recipe I use to “feed” my Christmas tree.
I got it online somewhere a long time ago but modified it to not use bleach.

How to Make Your Christmas Tree Fire Resistant
(and keep it living til 3 King’s Day!)

Ingredients:
• 2 cups of Karo Syrup
• 2 ounces of vinegar
• 2 pinches of Epson Salt
• ½ teaspoon of Borax (some recipes also call for 1 teaspoon of chelated iron which you can get at a pharmacy or garden store- I’ve never used it though.)
• 2 ground up aspirins
• Hot Water

Procedure:
1. With a saw, make a fresh cut at the base on the tree trunk. Cut off at least an inch and try to make a flat or level cut.
2. Immediately after cutting the base off the tree, mix the fireproofing ingredients listed above. Fill a 2-gallon bucket with hot water to within 1 inch of the top and add the ingredients. Stir thoroughly.
3. Stand the trunk of the tree in this solution and leave for 24 hours.
4. Every day, without exception, fill up the well of the tree-stand with the fireproofing solution.

How this procedure works:
The Karo Syrup provides the sugar necessary to allow the base of the tree to take up water. The tree may take up to 1/5 gallons of water over a two-week period. Boron in the Borax allows the tree to move the water and sugar out to every branch and needle in the tree. Magnesium compounds in the Epson Salt and Iron from the Chelated Iron provide essential components for the production of chlorophyll that will keep the tree green. The vinegar keeps mold from forming in your solution. This fireproofing procedure will also help prevent the needles from dropping and will increase the natural fragrance of the tree.

They say you can try to light a branch once it’s sat for 24 hrs and it won’t catch on fire! I love that it does keep my tree nice and green until I want to take it down after New Year’s.