To Trim the Stem or Not to Trim
Some orchids, such as the popular phalaenopsis or moth orchid, can bloom multiple times on the same stem. On this type of orchid, trim the stem no more than halfway back after all the flowers have dropped off. Doing this will maintain structural integrity by not letting the stem get so leggy that it snaps from the weight of the flowers. Also, trimming the flower spike often initiates the growth of a branch that will put out buds.
On other types of orchids, the stem will progressively turn brown and dry after the bloom cycle is complete. Do not cut the stem until it is fully dry. Let the plant pull all the nutrients back out of the stem before you remove it. These types of orchids bloom only once per stem and will grow a fresh one to bloom anew.
Feed Your Orchid
Your orchid does not go dormant; it just does things that are less fun to watch. It is important that you help your plant build up the energy to rebloom by feeding it, giving it the right amount of light, and watering the plant properly. The potting medium used for orchids is generally very light and airy so that it will drain well. It is also nutritionally deficient. Feed your orchid at least once a month with a balanced plant food; twice is even better. "Balanced means that the numbers on the label should be close in value, i.e., 20-20-20, 6-8-7 or 10-12-10. If the fertilizer you find is not formulated especially for orchids, you must dilute it to half the usual strength. Orchid roots will burn easily. If it is an orchid-specific food, then it has been formulated to be safe for orchid roots and no extra step is necessary.
Water Your Orchid Properly
The majority of orchids available for purchase are epiphytes. That means that their natural orientation is to grow caught up in the branches of trees and cascade freely. Gravity pulls excess water away from the roots of the plants, so even though they are tropical, they are accustomed to being well drained. Overwatering an orchid is the fastest way to kill it. Let the top of the potting mix dry out between waterings. Remember that all plants will bounce back from a drought, but none come back to life if they've been drowned.
Give Your Orchid the Right Amount of Light
Orchids must get the right amount of light to rebloom. The right amount of light is dependent on the type of orchid. Some are happy in full sun; some love shade. If you give them too much light, the leaves will sunburn and stress the plant. If you give them too little light, the leaves will be a dark green, storing too much chlorophyll and never getting the trigger to initiate a bloom cycle. Know what type of orchid you have and what it requires.