ROB LOWE was on “Ellen” earlier this week, and he said he’s OBSESSED with Christmas trees, and that the tree is “all he cares about during the holidays.”

And he can’t bear to see them dry out.  He said, quote, “I have a phobia about the pine needles getting all brittle and falling, and it’s going to be flammable.”

So he’s found a SECRET to making them last.  He puts 7-Up in the tree stand.  Actually a lot of it.  The reservoir is always filled with half 7-Up and half water.

A few people were very confused by this . . . but Rob isn’t the only one who does it.  It IS a Christmas tree “hack” that’s been passed down over the years.  Some people say the trees need sugar and citric acid to help them absorb the water.

Others believe you should add aspirin or bleach in with the water.  The thought behind that is that it prevents mold.

(And possibly kills your dog.  But hey, at least you squeezed a few more days out of that Christmas tree!)

So does 7-Up work?  Well, no . . . probably not.

The Executive Director of the National Christmas Tree Association, which IS a thing, says, quote, “We hear about all kinds of things people do to their trees.  We recommend just water . . . what the tree used while it was growing.”

He does have a few ACTUAL tips though . . .

The fresher the tree the better . . . and before putting it into the stand, cut an inch or so off the bottom, and get it in water immediately.  It’ll close off with sap if it is left out of water for more than two hours.

He adds, quote, “Don’t let the new cut on the trunk go dry, it needs to remain under water during the whole time it is in your home.

“Treat it like a fresh cut flower in a vase.  If you follow those tips, your tree will drink a lot of water in the first week to 10 days and be good for the whole season.”

(Here’s video of Rob.  Skip to the 4:20 mark.  If you want to try Rob’s 7-Up method, go for it.  But don’t be an IDIOT and put aspirin, bleach, or any other toxic stuff in your tree’s water if you have pets.  Or kids.)