You went to the grocery to get a quart of milk and came home with an orchid. How did that happen? An even more pressing question might be, "What do I do with it?" Don’t panic. Just follow a few basic guidelines, and you should be able to keep your plant alive and even re-bloom it.
This is the most critical step. More orchids are killed with kindness (overwatering!) than anything else. Put your finger in the growing mix. If it feels moist, don’t water until the mix feels dry. If the mix is dry, water it at the kitchen sink until the water runs through the pot. Never let the plant sit in water. If in doubt, don’t water.
Your orchid is probably a Phalaenopsis, the most popular orchid in displays at groceries and box stores. Phalaenopsis have broad, flat leaves and stems of white or brightly colored flowers. They like low light conditions and do best in east-facing windows. They also do well in southern or western windows. But don’t place your plant next to the glass of a western window because the sun’s rays could burn its leaves. Northern windows do not receive enough light for your plant to re-bloom.
Like you, your orchid will be most comfortable if the temperature is between 60 degrees F and 80 degrees F. You will increase its chances of re-flowering if your house is cooler at night than during the day. A drop of 10 F is not too much. A night rest allows it to save energy it has made during the day from photosynthesis. Think of this as a plant-energy savings account that pays dividends in flowers.
Use a fertilizer made for orchids. These are readily available at garden centers. Follow package directions. A good practice is to fertilize for three waterings and flush with clear water at the kitchen sink on the fourth watering to remove fertilizer salts.
This is the biggie. People usually have a Butterfly McQueen-type reaction to repotting an orchid. McQueen, as the maid, Prissy, in "Gone With the Wind," famously exclaimed: "I don't know nothin' 'bout birthin' babies!" Repotting orchids is nothin' like "birthin' babies." As soon as the plant finishes flowering, cut off its flowering stem, remove it from the pot, ease as much potting mix off the roots as possible (swishing in water helps) and repot it in a plastic container just barely bigger than the root ball — no matter how large the leaves are. Orchids like to be under-potted. Mixes found at garden centers should do fine. Work the mix around the roots until the plant is snug in the pot and you can pick it up by the stem and it does not come out of the pot. Be careful not to break off any tender green or brown root tips, and don’t force roots that want to wander in the air into the pot.
Because your plant is probably a Phalaenopsis, a decrease in day length and night temperatures usually helps it to begin the flowering process. Because these conditions naturally occur in the fall, place your plant outside at night as long as temperatures are above 55 degrees F. Be sure to put it where dew will not collect in the crown. Bring it inside during the day unless it’s located in a spot where it will not get direct sunlight. Hopefully, you’ll have flowers in January or February. If not, there will be more orchids in your grocery strategically placed for an impulse buy, which may be how your plant came home with you to begin with.