Keeping roses fresh once are cut
 

Hello,

I have a garden with several kinds of roses and from time to time I like to
cut some and put them inside the house. I wonder if anyone knows about
techniques to keep them fresh for long time, apart from placing them in
water. I heard that cuting the stem each day one or two centimeters in
diagonal helps in that way, but I don't know if it's true. Maybe placing
something in the water? Although it's not my best choose, any chemical
product?

Regards,

Roger