"slit up" is correct and can be used in written English.
It means to cut or tear something in a long, narrow opening, usually from bottom to top or side to side. Example: The seamstress carefully slit up the back of the dress to add a bit of flair to the design.
Balmain was dominated by knitwear albeit, in a Balmain way, slit up to the middle of most models' thighs.
Drawn in a pulpy nineteen-eighties style, Marra's Dowd has a wild red mane, a skirt slit up to there, and a handgun stuffed in her garter.
The tops of her above-elbow black gloves are precisely parallel with the border of her strapless (and slit up to there) black gown.
Fiery, sexy and sultry, Ms. Stone commands the stage from her first entrance with her long black hair flowing like a Medusa and her dress slit up to her thighs.
PARIS — "If we men could wear our clothes slit up to the knee, too, it wouldn't be so bad," said a man on one of the boulevard cafe terraces yesterday [July 15] afternoon.
And the all-over Fabergé-inspired embroidery was echoed as a laser-cut pattern on emerald green velvet, such as on a floor-length skirt with an Angelina Jolie-worthy slit up the right leg.
In the center of the lobby is the Gazebo Lounge, where waitresses in long skirts slit up to the thigh serve pricey whiskey, or sweets such as white chocolate crème brulee and lemon- coconut cheesecake.
Dip in flour and fry, slit side up, until cheese melts.
Pieces that elongated the body — monochromatic dresses and lean, slit-up-the-side skirts — sent the strongest message about this season's silhouette: flattery was everything.
Grab both ends of the potato with your fingers (slit side up) and push down and in.
But this was just a quick slit, bundle up the roots, slip them in, and close up the slit with your boot.
