Most people know this quote from Shakespeare (Hamlet Act IV, Scene V). But why would Ophelia have said this? If I recall correctly, she was mad at this point and probably didn’t have any real reason behind the statement. However, Rosemary Rosmarinus officinalis has a long reputation for strengthening the memory. From this, it became an emblem of friendship and fidelity for lovers. It is said Anne of Cleves (one of Henry VIII’s wives) wore a wreath of Rosemary at her wedding; we still use it in wedding decorations. It is used at funerals even today (especially in Wales) as a sign of friendship to the deceased.
Rosemary is an antidepressant and antimicrobial. In earlier times, it was both burned as incense and strewn in hospitals to purify the air and prevent infections. I put a few drops of Rosemary essential oil in the spray I use to clean the kitchen and bathroom. Things smell great and germs don’t like it. It’s also antispasmodic and a rubefacient (reddens the skin which means you’re stimulating blood flow in the capillaries close to the surface) so either using a Rosemary-infused oil or putting a few drops of the essential oil into a cream really helps when massaging muscle cramps and for nerve pain. Ladies, because it’s antispasmodic, a cup of Rosemary tea two or three times a day may help with those monthly cramps.
I use a diluted apple-cider vinegar infusion of Rosemary as a final rinse when washing my hair. The vinegar rinses out the last remains of the soap and Rosemary is great for dark hair (I do still have some hair that’s brown instead of gray). Maud Grieve says that Rosemary has the “effect in stimulating the hair-bulbs to renewed activity and preventing premature baldness … It forms an effectual remedy for the prevention of scurf (scale) and dandruff.”
Rosemary is originally a Mediterranean plant – it likes to be warm and somewhat dry. However, it grows well in just about any climate with care, including in a pot in your house. If you choose to bring yours indoors, be sure they get quite a bit of sunlight wherever you place them. (Check with your local nursery for a varietal that is hardy in your area. My favorite is ‘Tuscan Blue’, which seems to be hardy most everywhere. It is the plant in the picture.) Although our winters aren’t nearly as bad as those further north, it gets cold enough to kill these warmth-lovers, so I make them their own little greenhouse for the winter with stakes and plastic. 
The parts used are the leaves (needles) and twigs. It has a high volatile oil content, which is why it has such a strong smell. Even though you’d think from the aroma and the way it looks that it would be a member of the same family as pine trees, it’s not! It’s in the same family as mints. I find it easiest to use just the leaves so you can strip the leaves for use and then the twigs make wonderful kebab skewers.
Rosemary is a great protective and purification plant and makes a wonderful substitute for White Sage when you’re purifying an area. An infusion of Rosemary can be used to purify magical tools and it’s suggested you wash your hands in a Rosemary infusion prior to performing healing spells. It can also be added to spells for fidelity or to strengthen mental powers.
Even if you do nothing more than inhale Rosemary’s wonderful aroma, I strongly suggest you make friends with this versatile plant.