Any plant can be grown hydroponically, but some plants are more commonly grown that way than others. Most hydroponic gardens are constrained by small hydroponic units or greenhouses, so plants that take up little space are typically preferred. Large plants such as squash, corn and pumpkins are not typically grown with this method. Houseplants and herbs also do well in hydroponic gardens.
Hydroponic tomatoes are very common; many grocery stores carry these tomatoes, especially during winter months.
Some varieties of tomatoes have been especially propagated for hydroponic growth. The University of Arizona notes that, "Some of the more popular varieties are Apollo, Belmondo, Caruso, Dombito, Larma, Perfecto, Trend and Trust."
These varieties do not stop growing after flowering and will grow long vines that need to be trained toward the top of the greenhouse using string.
Tomatoes need to be kept at a temperature of at least 70 degrees during the day, and 61 degrees at night. The plants need to have enough humidity during photosynthesis; 65 percent at night and 80 to 90 percent during the day. Higher humidity can negatively affect the tomatoes--fruit production becomes reduced and quality diminishes.
Tomato flowers must be pollinated either mechanically, by shaking the flower clusters every other day, or by maintaining a beehive inside the greenhouse.
Herbs are a common choice for hydroponic gardening because they take up very little space and do not require more than basic nutrients. Basil, dill, coriander, chives, oregano, rosemary, sage and thyme are some of the herbs to grow.
Most herbs can be grown using only one nutrient solution. They do best at a temperature between 75 and 85 degrees. Many herbs are susceptible to fungal infections and can be bothered by mites, whitefly and leafminer.
When harvesting herbs, never take more than half the leaf area at one time; herbs tend to grow slowly.
Orchids often grow hydroponically in nature, clinging to moss-covered rocks or tree trunks and collecting water run-off with their exposed roots. Hydroponic gardeners are often able to grow orchids more easily than traditional gardeners because they can closely control the amount of water each plant receives.
Some orchid varieties need a lot of light and will do best with supplemental lighting. These plants will require extra water and nutrients. Be careful not to over-water; make sure that roots are almost completely dry before watering.
Ventilation is also important for hydroponic orchids. The high humidity they require is also a good environment for fungus. A well-placed fan can retard fungus growth.