Monica Buck

Properly cared for, sheets should last three to five years. For
the longest wear, follow these rules:
Avoid very hot temperatures when washing and drying; they
weaken fibers.
Use mild detergent (such as Wisk or Arm & Hammer dye-free
formula) and wait until it's diluted before putting sheets in
the washer. Undiluted detergents can discolor fabric. And don't
overdo the detergent: If it isn't completely rinsed out, sheets
will feel stiff. Use half the manufacturer's recommended amount,
and add one cup of white vinegar to the rinse water to remove
all traces of detergent.
Avoid brighteners and other bleaching agents; they weaken and
discolor fibers. To brighten whites, add 1/4 cup lemon juice to
the wash cycle instead of bleach.
Dry on the low or medium heat setting; overdrying sheets weakens
fibers and bakes off finishes.
Store laundered, completely dry sheets in a dry, cool place away
from direct sunlight.
Keep three sets of sheets for each bed and rotate weekly.
To keep sets together and the linen closet neat, store each set
in a matching pillowcase.